Neuroscience Quiz 2

Circadian Control of sleep

-Photic Stimulation of Retina -Activation of retinohypothalamic fibers -Stimulation of suprachiasmatic nucleus SCN -Activation of sympathetic fibers via SCN -Stimulation of Pineal gland -Release of Melatonin -Rhythm of Sleep-wake cycle

Higher Cortical Functions

Language Speech Learning Memory

Temperature Regulation

requires the integration of a number of processes associated with hypothalamic functions. These include: Activation of thermoreceptors that can respond to increases or decreases in blood temperature; The capacity of the hypothalamus to activate TRH, which leads to secretion of TSH, with subsequent secretion of thyroid hormone for increases in metabolic rates; Activation of autonomic mechanisms, which, in turn, dilate or constrict peripheral blood vessels that serve to cause loss or conservation of body temperature, respectively; and Activation of behavioral responses, such as panting (to generate heat loss) and shivering (to conserve heat).

Nocturnal Enuresis

Bed-wetting during sleep. Usually after 3 - 4 hrs of sleep in stage 3 or 4 of slow wave sleep. Indicates failure of neural regulation of micturition

Brain Structures Involved in Memory

* Hippocampus - bridge between STM and LTM, handles many explicit memories * Frontal and temporal lobes store long-term memories * Cerebellum - classical conditioning * Basal Ganglia - procedural memory

Motor and Sensory Areas of the Cortex

-Central sulcus separates motor and sensory areas -Motor areas *Precentral gyrus (primary motor cortex) of frontal lobe: directs voluntary movements -Sensory areas *Postcentral gyrus (primary sensory cortex) of parietal lobe: receives somatic sensory information (touch, pressure, pain, vibration, taste, and temperature)

Structural Changes in memory

Occurs in synapses during the development of long-term memory : Increase in vesicle release sites for secretion of transmitter substance Increase in number of transmitter vesicles released Increase in number of presynaptic terminals Changes in structures of the dendritic spines that permit transmission of stronger signals

Associative learning

Occurs when 2 stimuli are associated with each other such as Pavlov's classic experiment.

Broadmann's areas

On the basis of variations in the histology of layers I-VI, Brodmann divided the cerebral cortex into 47 areas. Most of Brodmann areas are used synonymously with functionally specific areas.

Functions of the limbic system

P.D. MacLean (1949) called limbic system as visceral brain for its close association with hypothalamus & visceral autonomic functions. Limbic system is primarily involved in Motivation Reward system Avoidance system Addiction Emotions Fear, anxiety, Rage, & Aggression Sexual activity Autonomic responses

Nonassociative learning

A change in behavior that takes place after repeated exposure to a single stimulus. It includes Habituation and Sensitization. Both occur in many situations, but always require repeated exposure to a stimulus. They are necessary in designing control procedures in classical conditioning and have a role in operant conditioning

Reticular Formation Inputs and Outputs

Ascending projections Intrinsic connections Descending projections

Stages of Sleep

Awake to Drowsy First subject becomes drowsy EEG shows a change from beta to alpha rhythm. 1. Lightest Sleep (NREM) 2. Slightly Deeper Sleep (NREM) 3. Deeper Sleep (NREM) 4. Delta Waves are omitted but there is not much difference between this stage and stage 3 (NREM) 5. REM

Broca's aphasia

Caused by a lesion of the motor speech center in area 44,45 and the neighboring areas 9, 46, and 47. Spontaneous speech (verbal output) is grammatically incorrect and the patient typically communicates by using single words and is incapable of repeating someone else's words (impaired repetition ability). Language comprehension is not, or less markedly, impaired. As a rule patients cannot write normally. However, if the lesion is limited to area 44, the ability to write is preserved (a rare disorder, called aphemia).

Fear

Centers for fear reaction: hypothalamus & amygdala. Amygdaloid nucleus also encode the memories that evoke fear. In humans, left amygdala is activated by looking at the ugly faces that evoke fear, which does not occur by looking at joyful faces.

Hyperthermia

Characterized by high temperature that could be fatal. It is sometimes associated with surgery involving the region adjacent to the pituitary and is believed to involve the anterior hypothalamus that controls the heat loss mechanism.

Abnormal Involuntary Movements

Choreoathetosis with ataxia may follow vascular lesions of the thalamus. It is not certain whether these signs in all cases are due to the loss of function of the thalamus or to involvement of the neighboring caudate and lentiform nuclei. The ataxia may arise as the result of the loss of appreciation of muscle and joint movement caused by a thalamic lesion.

Insomnia

Chronic inability to sleep in spite of adequate opportunity to do so Primary insomnia: normal nocturnal sleep is disturbed chronically. Secondary insomnia: secondary to medical or psychological disorders.

Addiction

Compulsion of repeated use of a substance in spite of knowing negative impact of the substance on health. Primary center: Nucleus accumbens. Major mechanism of addiction is increased dopamine concentration in reward system of brain. Ventral tegmental area projecting to nucleus accumbens through mesocortical dopaminergic fibers is the major afferent pathway.

Global aphasia

Damage to both the sensory and the motor centers, e.g., by occlusion of the medial cerebral artery Both spontaneous speech and comprehension are impaired.

Motivation

Different areas in brain on stimulation produce either pleasant feeling (rewarding) or unpleasant feeling (aversive) About 35% of brain areas are rewarding, 5% are aversive & 60% neutral in nature. These areas are detected by animal experiments.

Electroencephalogram (EEG)

Electroencephalography- Recording of electrical activity of brain with surface electrodes placed on scalp. Record= electroencephalogram (EEG) Algebraic summation of excitatory & inhibitory postsynaptic potentials (EPSPs & IPSPs) from large number of cortical neurons. 10-20 international system of electrode placement Bipolar recording- potential difference between two active electrodes Monopolar recording- records between active & indifferent electrode

Episodic memory

Events that you personally experienced at a specific time and place. It includes memories such as the meal you ate last night, or the name of an old classmate, or the date of some important public event.

Neural mechanism of learning and memory

Every time you learn something, neural circuits are altered in your brain. These circuits are composed of a number of neurons (nerve cells) that communicate with one another through special junctions called synapses. Memories are stored in the brain by changing the basic sensitivity of synaptic transmission between neurons as a result of previous neural activity. Neural change responsible for retention and storage of knowledge is known as the memory trace Once the traces are established, they can be selectively activated by the thinking mind to reproduce the memories.

Interposed Nucleus

Paravermal portion of spinocerebellum projects here

Declarative Memory

(Explicit) Memory of all those things that you are aware of remembering and that you can describe in words, such as your birthday, or the meaning of the word "cradle", or what you ate last night. This form of memory is also called explicit memory, because you can name and describe each of these remembered things explicitly. Two types Semantic memory Episodic memory

Wernicke (sensory) aphasia

● Characterized by poor comprehension, fluent speech, poor repetition, and quadrantanopia also marked by paraphasic errors such as non sequiturs (latin—does not follow logically what is said previously), neologisms (words with no meaning), and driveling speech. ● Results from a lesion in the posterior temporal lobe, in the superior temporal gyrus (brodmann 22).

Conduction aphasia

● Involves the transection of the arcuate fasciculus; the arcuate fasciculus interconnects broca speech area with wernicke speech area. ● Characterized by good comprehension, poor repetition, and fluent speech.

Major efferents from the cerebellum

-Spinocerebellum (Intermediate hemisphere) -Vestibulocerebellum (Flocculonodular lobe) -Cerebrocerebellum (Lateral hemispheres)

Cerebellar cortex layers

3 Neuronal Layers 1. Molecular - outer - basket cells and stellate cells - both use GABA to inhibit Purkinje cells - parallel fibers = granule cell axons 2. Purkinje cell layer - GABA - dendrites of purkinje cells extend into molecular layer 3. Granule cell layer - Golgi and Granule cells = form synaptic glomeruli (each contains a cell body of granule cell and axons of mossy fibers/Golgi cells that synapse with granule cells) *- Granule cells = Glutamate, project to molecular layer Purkinje cells* - Golgi = GABA to purkinje cells

Narcolepsy

A chronic neurological disorder characterized by excessive day time sleepiness and abnormalities of REM sleep for a period of greater than 3 months. Have mixed signals sent from their brain about when to sleep, which is why narcoleptics fall asleep at inopportune times. Excessive daytime sleepiness is the first noticeable symptom of narcolepsy. It can take a number of years for this symptom to progress to a point of concern and for other related symptoms to present. Cataplexy: is a sudden loss of muscle tone that causes feelings of weakness and loss of voluntary muscle control. Usually cataplexy is the second symptom to present after EDS. Sleep Paralysis: is literally the paralysis brought on by ones mind and body entering into REM sleep. This occurs naturally every night when a person is sleeping. When sleep paralysis occurs with narcolepsy, it can happen at any point during ones wakeful hours. Hallucinations

Papez Circuit

A circuit of structures interconnecting the hypothalamus and cortex, proposed by Papez to be an emotion system Hippocampal formation Mamillary body Thalamic anterior nucleus Cingulate gyrus Amygdala Hypothalamus Cerebral cortex Fornix Mamillothalamic tract Thalamocortical radiation Cingulum

Connections of Thalamus

Inputs from Basal Nuclei, Cerebellum, Sensory, Visual, and Auditory Outputs to Limbic System, Frontal lobes, Parietal Lobe, Cingulate Gyrus and Association areas or Cerebrum.

Sleep Apnea

A disorder characterized by the cessation of airflow at the nose or mouth during sleep. These apneic episodes usually last longer than 10 sec each. Pathologic if >5 episodes /hour or >300/night Types: Obstructive: Muscle atonia in oropharynx, nasal, tongue or tonsil obstruction Central: lack of respiratory effort Symptoms: Usually seen in obese, middle-aged males Sometime associated with depression, mood changes and daytime sleepiness Complaints of dry mouth, may have headache in the morning

Frontal Lobe

A large part of the frontal cortex rostral to the central sulcus is related to the control of movements, primarily on the opposite side of the body. These areas include primary motor cortex (Brodmann area 4), premotor cortex (area 6), the frontal eye field (area 8), and the motor speech areas of Broca (area 44 and 45). Premotor cortex Just anterior to area 4 is the premotor cortex (area 6). Neurons here are particularly active prior to the activation of area 4 neurons, so it is thought that the premotor cortex is involved in the planning of motor activities. Damage here results in an apraxia, a disruption of the patterning and execution of learned motor movements. Individual movements are intact, and there is no weakness, but the patient is unable to perform movements in the correct sequence. Prefrontal cortex This area is involved in organizing and planning the intellectual and emotional aspects of behavior, much as the adjacent premotor cortex is involved in planning its motor aspects.

Internal capsule

A layer of white matter (myelinated axons) that separates the caudate nucleus and thalamus medially from the lentiform nucleus laterally. Consists of three divisions: A. Anterior limb: Located between the caudate nucleus and the lentiform nucleus. B. Genu : Contains corticobulbar fibers. C. Posterior limb: Located between the thalamus and the lentiform nucleus. ● Contains the sensory radiations (pain, temperature, and touch). ● Contains the corticospinal fibers. ● Contains the visual and auditory radiations.

Functional anatomy of thalamus

A nuclear complex located in the diencephalon and comprising of four parts (the hypothalamus, the epythalamus, the ventral thalamus, and the dorsal thalamus). The thalamus is a relay centre subserving both sensory and motor mechanisms.

Basal Ganglia

A set of subcortical structures that directs intentional movements structures in the forebrain that help to control movement

Hypothalamus

A small structure in the brain lies on each side of the 3rd ventricle. It weighs about 10g. Located below the thalamus. It consist of large group of nuclear groups: Anterior, Middle, Posterior and Lateral

Rapid eye movement (REM) sleep

A state of sleep characterized by aroused EEG patterns, sexual arousal, saccadic eye movements, generalized muscular atony, elaborated visual imagery (dreaming), An awake brain in paralyzed body EEG Patterns: Brust of sawtooth waves or Ponto-geniculo-occipital (PGO) spikes Easiest to arouse

Split brain syndrome

A structure known as the corpus callosum connects the left and right hemispheres of the brain and enables communication between them. Dysfunction or absence of this structure can result in a condition known as split-brain syndrome, in which each hemisphere of the brain functions independently. Split-brain syndrome is associated with conditions such as alien-hand syndrome, which is characterized by involuntary and uncoordinated yet purposeful movement of the hands.

Tics

A sudden brief action that is preceded by an urge to perform it and is followed by a sense of relief is called a tic. Motor tics usually involve the face or neck and, less often, the extremities. Vocal tics can be brief grunts, coughing sounds, howling or barking-like noises, or even more elaborate vocalizations that sometimes include obscene words (coprolalia). Tic disorders make up a spectrum ranging from transient single motor or vocal tics of childhood to Tourette's syndrome (also known as Gilles de la Tourette's syndrome), which is characterized by persistent motor and vocal tics.

Jet lag

A syndrome associated with flights across two or more time zones. It is characterized by sleep disturbance, excessive daytime sleepiness, reduced performance, gastrointestinal problems (eg, constipation), and generalized malaise due to circadian misalignment. Not all the components are present in every case, and individuals may vary in their susceptibility to jet lag symptoms. Pathophysiology: temporary desynchronization between the sleep and wake cycle generated by the endogenous circadian clock and the environmental rhythm in the destination time zone. The sleep/activity cycle is particularly affected, which leads to changes in physical and mental functioning.

Romberg's test

A test used in an exam of neurological function. It is based on at least two of the three following senses to maintain balance while standing: proprioception; vestibular function and vision With the eyes open, three sensory systems provide input to the cerebellum to maintain truncal stability. These are vision, proprioception, and vestibular sense. If there is a mild lesion in the vestibular or proprioception systems, the patient is usually able to compensate with the eyes open. Romberg's test is positive if the patient sways or falls while the patient's eyes are closed. When the patient closes their eyes, however, visual input is removed and instability can be brought out. If there is a more severe proprioceptive or vestibular lesion, or if there is a midline cerebellar lesion causing truncal instability, the patient will be unable to maintain this position even with their eyes open. Sensorimotor integration is carried out by the cerebellum and by the dorsal column-medial lemniscus tract. The motor pathway is the corticospinal (pyramidal) tract and the medial and lateral vestibular tracts. Romberg's test is not a test of cerebellar function but can be helpful in identifying truncal ataxia and may help differentiate cerebellar lesions from lesions of the vestibular or proprioceptive systems.

EEG Waveforms

According to its frequency, 4 types Alpha waves Recorded - awake & relaxed with closed eyes Marked in parietal & occipital region Frequency= 8-12 Hz & amplitude= 50-100µV Beta waves Awake & alert, mentally busy or tense condition 13-30 Hz of lower amplitude Marked over frontal regions Theta waves 4-7 Hz, larger amplitude than alpha waves Awake children (parietal & temporal region), emotional stress & in light sleep in adult Delta waves <4 Hz & average amplitude 100 µV In deep sleep & infancy Upto 2 years of age- awake EEG- in delta range From 2-6 years of age- awake EEG- theta range Then only alpha rhythm appears & is the characteristics of awake in relax state in adult

Chemical Control of sleep

Acetylcholine: fibers from dorsal pontine tegmentum selectively promote REM sleep. Adenosine: induces sleep; antagonist (caffeine) produces alertness. Prostaglandin: increase concentration of PGD2 in medial preoptic area induces sleep & ↑ed concentration of PGE2 decrease slow wave sleep & produce wakefulness. Serotonin: fibers from raphe nucelus to thalamus & cortex; agonists suppress sleep & antagonists induce slow wave sleep. Norepinephrine: fibers from locus ceruleus to cortex on stimulation prevent sleep; descending fibers inhibit motor neurons that produce hypotonia during slow wave sleep.

Learning

Acquirement of information or knowledge by experience that results in alteration of behavior. Can be classified into: 1. Associative Learning 2. Nonassociative Learning

Neural Control of Sleep

Afferent control Repeated & monotonous stimulation of mechanoreceptors or afferents from these receptors at the frequency < 10 Hz produces sleep. Central Control Diencephalic zone: posterior hypothalamus & intralaminar & anterior thalamic nuclei. Medullary zone: reticular formation at the level of NTS Basal forebrain zone: preoptic area of hypothalamus & diagonal band of Broca. Circadian control The suprachiasmatic nucleus (SCN) is the biological clock which is influenced by the light dark cycle through retinohypothalamic pathways.

Wernicke area

It is located in the superior temporal gyrus and extends around the posterior end of the lateral sulcus into the parietal region. This area of the cortex is dedicated to the comprehension of both signed and spoken language and allows us to interpret and assign meaning to symbols.

Stage II Sleep

Amplitude of EEG waves slightly increases. EEG Patterns: Sleep spindles & K-complexes Sleep Spindles Bursts of Alpha like waves with frequency of 12 - 14 Hz & amplitude of 50 µv, each lasting for 2 sec. Called sleep spindles because of characteristic waxing & waning amplitude. K-Complexes High amplitude-sharp waves appearing irregularly in EEG. Eyes are generally still and heart and breathing rates decrease only slightly. Sleep is not deep. Longest of all the sleep stages

Huntington's Disease

An autosomal dominant neurodegenerative condition characterized by a progressive, usually choreiform movement disorder, dementia, and psychiatric disturbances, ultimately leading to death. Clinical onset is usually between 20 and 40 years of age. The disease is progressive and usually leads to a fatal outcome within 15-20 years. The initial symptoms may consist of either abnormal movements or intellectual changes, but ultimately both occur. Gradual onset and progression of chorea and dementia or behavioral change. Cause Due to degeneration of GABAergic striatonigral pathway. GABAergic & cholinergic neurons are lost in the striatum.

Friedreich's ataxia

An inherited disease that causes progressive damage to the nervous system, resulting in symptoms ranging from gait disturbance to speech problems; it can also lead to heart disease and diabetes. This ataxia results from the degeneration of nerve tissue in the spinal cord, in particular sensory neurons essential (through connections with the cerebellum) for directing muscle movement of the arms and legs.

Parallel fiber activation

Can lead to a beam of excitation within the plane of the parallel fiber and the Purkinje cell neurons with which they make synaptic contact and inhibition along adjacent beams of Purkinje cell neurons. The parallel fiber excites basket cells, which are inhibitory and make synaptic contact with Purkinje cells located in adjacent planes. This provides the basis for inhibition along the beam of Purkinje cells adjacent to the beam of excitation of Purkinje cells induced from the parallel fiber. The diagram also illustrates the relationship of the Golgi cell in inhibiting granule cell activity, as well as the inputs into the deep cerebellar nucleus, which constitutes the output neuron of the cerebellum. Such inputs include excitation from mossy and climbing fiber collaterals and inhibition from the Purkinje cells. Mossy fibers also excite granule cells, and climbing fibers excite Purkinje cells.

Components of Basal Ganglia

Caudate nucleus Putamen Globus pallidus External Segment Internal Segment Subthalamic nucleus Substantia nigra Pars Compacta Pars Reticulata

Broca area

It is located in the inferior frontal gyrus of the frontal lobe, just anterior to the inferior part of the precentral gyrus. This area of the cortex is dedicated to the production of language, which includes spoken as well as written and sign language. This area of the cortex can produce symbols (signs or words) for concepts, objects, ideas, etc.

Cerebellar divisions

Cerebellum is divided into -Cerebellar cortex (outer part) -Deep cerebellar nuclei (inner part)

Gait apraxia

Characterized by diminished cadence, wide base, short steps, and shuffling progression; it is reminiscent of parkinsonian gait. ● A frontal lobe sign seen in normal-pressure hydrocephalus with gait apraxia, dementia, and incontinence.

Broca (motor) aphasia

Characterized by good comprehension; effortful, dysarthric, telegraphic, and nonfluent speech; poor repetition; and contralateral lower facial and upper limb weakness. ● Results from a lesion in the frontal lobe, in the inferior frontal gyrus (brodmann 44 and 45).

Clinical Features of Huntington's disease

Chorea: Rapid, involuntary & dancing movements Loss of GABAergic neurons in striatum → removes inhibitory influence on globus pallidus → reduces activities in thalamic nucleus Dementia: Due to simultaneous & progressive loss of cholinergic neurons in cerebral cortex The earliest mental changes are often behavioral, with irritability, moodiness, antisocial behavior, or a psychiatric disturbance, but a more obvious dementia subsequently develops. Gradually, speech is slurred in Huntington disease The pathologic hallmark of Huntington's disease is progressive atrophy of the striatum, especially involving the caudate nucleus. No definite treatment Disease is progressively fatal

Purkinje Cell Layer

Contains Purkinje cells, the largest neurons with extensive dendritic branches Inputs: fibers from molecular layer & climbing fibers, & parallel fibers. Outputs: dendrites into molecular layer; axons into deep nuclei Hence, Purkinje cells are connecting link b/w cerebellar cortex & deep cerebellar nuclei.

Molecular Layer

Contains interneurons Basket cells Stellate cells Inputs: parallel fibers from granule cells Outputs: dendrites & cell bodies of Purkinje cells.

Granular Cell Layer

Contains interneurons - granule cells & Golgi cells Golgi cells located in the granule cell layer and provides inhibitory feedback to the granule cells Granule cells receive inputs from mossy fibers. Granule cells project to Purkinje cells, basket cells, stellate cells & Golgi cells via parallel fibers.

Cerebellar Functions

Control of postural balance & equilibrium Vestibulo-ocular reflex Smoothes & coordinates movement Control of skilled voluntary movements Planning & programming of the movements Internal Circuitry Control of muscle tone & stretch reflex Control of movement of one side of body Learning & improvement of motor skill Eye ball movement Vestibular functions

Basal Nuclei Grouping

Corpus Striatum Caudate nucleus Putamen Globus Pallidus Neostriatum or Striatum Caudate nucleus Putamen Lentiform Nucleus Putamen Globus Pallidus Paleostriatum Globus Pallidus Externa Globus Pallidus Interna

Cortical and subcortical limbic areas

Cortical areas: Limbic lobe Orbitofrontal cortex: a region in the frontal lobe involved in the process of decision-making Piriform cortex: part of the olfactory system Entorhinal cortex: related to memory and associative components Hippocampus and associated structures: play a central role in the consolidation of new memories Fornix: a white matter structure connecting the hippocampus with other brain structures, particularly the mammillary bodies and septal nuclei Subcortical areas: Septal nuclei: a set of structures that lie in front of the lamina terminalis, considered a pleasure zone Amygdala: located deep within the temporal lobes and related with a number of emotional processes Nucleus accumbens: involved in reward, pleasure, and addiction Diencephalic structures: Hypothalamus: a center for the limbic system, connected with the frontal lobes, septal nuclei, and the brain stem reticular formation via the medial forebrain bundle, with the hippocampus via the fornix, and with the thalamus via the mammillothalamic fasciculus; regulates many autonomic processes Mammillary bodies: part of the hypothalamus that receives signals from the hippocampus via the fornix and projects them to the thalamus Anterior nuclei of thalamus: receive input from the mammillary bodies and involved in memory processing

Charcot's neurologic triad

Nystagmus, intention tremor, & scanning speech are seen in cerebellar disorder & disseminated sclerosis.

Deep Cerebellar Nuclei

Deep cerebellar nuclei project to different parts of the brainstem & thalamus. Fastigial Nucleus Interposed Nucleus -Globose Nucleus -Emboliform Nucleus Dentate Nucleus

Cerebellar Ataxia

Defect in coordination due to errors in the rate, range, force, & direction of movement If only cerebellar cortex is involved, ataxia is temporary. If the lesion involves deep cerebellar nuclei, ataxia is almost permanent. Features Drunken gait: unsteady & wide base gait. Scanning speech: scans the syllables while speaking Dysmetria: also called past pointing; inability to measure the length or distance Intention tremor: repeated overshoot & correction → hand oscillating back & forth; tremor not seen at rest Rebound phenomenon: inability to put on brake (suddenly stop) of the ongoing movement Adiadochokinesia (Dysdiadokinesia): inability to perform alternate movements rapidly Decomposition of movement: inability to perform movement that involves more than one joint simultaneously; patient dissects such complex movement & performs movement at each joint slowly & separately

Lesion of caudate nucleus

Delayed alternation & disrupt performance on tests involving object reversal.

Pathways of the basal ganglia

Direct and indirect

Functional anatomy of cerebrum

Divided into left and right hemispheres by a longitudinal fissure. The most conspicuous features on the surface of each hemisphere are numerous folds called gyri, which greatly increase the surface area of the cortex. The intervening grooves between the gyri are called sulci. The central sulcus is located between the precentral gyrus anteriorly, which is the primary motor cortex, and a postcentral gyrus posteriorly, which is the primary somatic sensory cortex. Each cerebral hemisphere is divided into lobes, which are named for the skull bones overlying each one. The frontal lobe is important in voluntary motor function, motivation, aggression, the sense of smell, and mood. The parietal lobe is the major center for the reception and evaluation of sensory information, except for smell, hearing, and vision. The frontal and parietal lobes are separated by the central sulcus. The occipital lobe functions in the reception and integration of visual input and is not distinctly separate from the other lobes. The temporal lobe receives and evaluates input for smell and hearing and plays an important role in memory. Its anterior and inferior portions are referred to as the "psychic cortex," and they are associated with such brain functions as abstract thought and judgment. The temporal lobe is separated from the rest of the cerebrum by a lateral fissure, and deep within the fissure is the insula, often referred to as a fifth lobe.

Functional Divisions of Cerebellum

Divided into three major subdivisions -Spinocerebellum (Paleocerebellum) -Vestibulocerebellum (Archicerebellum) -Cerebrocerebellum (Neocerebellum)

Lesion of head of left caudate nucleus

Dysarthric aphasia (difficulty in articulating words)

Kluver-Bucy Syndrome

Experimentally induced in rhesus monkey by bilateral temporal lobectomy, particularly involving amygdala. Features Placidity: there is marked decrease in aggressive behavior; the subjects become passive, exhibiting little emotional reaction to external stimuli. Visual agnosia (inability to recognize object visually inspite of good vision) Hypersexuality, hyperphagia, & hyperorality (examine everything orally) Hypermetamorphosis (fails to ignore peripheral stimuli, respond to every stimuli & explore everything) Similar features observed in human beings following -Bilateral surgical removal of temporal lobes -Cerebral atrophies -Meningoencephalitis due to toxoplasmosis, herpes simplex or AIDS.

Functions of Thalamus

Four basic functional roles: Sensory All sensory information (except olfaction) is relayed to the cortex via the thalamus Motor Motor system outputs from the basal ganglia and cerebellum are relayed by the thalamus Emotion/memory The thalamus is part of the Papez circuit and helps control some emotional and memory information going to limbic cortex (cingulate gyrus) Vegetative The thalamus has some intrinsic nuclei associated with alertness and arousal. Can be associated with disorders of consciousness

Cerebellum Disorders

General Features No sensory deficit No paralysis (defective but intact voluntary movements) Usually reflexes are normal (except sometimes pendular knee jerk) Usual feature - hypotonia Inability to carry out long-term adjustment in motor response. Defect in vestibulo-ocular reflex leads to pathological nystagmus

Sexual Dystrophy

Genital dystrophy can occur following lesions believed to be located in or around the tuberal region of the hypothalamus but that may extend to the ventromedial nucleus as well. This type of dystrophy is characterized by loss of sexual activity and genital atrophy. Other forms of alterations in sexual development may also occur from lesions, tumors (of the hypothalamus or of the pineal gland), encephalitis, or even hematomas of the hypothalamus. In children, the disorder (of the hypothalamus or of the pituitary gland) may result in retardation of sexual organs and sexual function. It is also possible for the disorder to lead to an opposite effect, resulting in premature sexual development of the genitalia.

Stage I Sleep

Heart and breathing rates decrease slightly, the eyes roll slowly from side to side, and an individual experiences a floating sensation. Light sleep during which alpha rhythm is replaced by low frequency & high amplitude EEG waves.

Reticular Formation Functions

Help to maintain consciousness. The RAS is also active during arousal, or awakening from sleep, inactive during sleep. Help to maintain attention and alertness. The RAS also prevents sensory overload by filtering out insignificant information so that it does not reach consciousness. The descending portion of the RAS has connections to the cerebellum and spinal cord and helps regulate muscle tone, Also assists in the regulation of heart rate, blood pressure, and respiratory rate.

Kernicterus

Hemolytic disease of newborn → ↑ indirect bilirubin → bilirubin crosses blood brain barrier → damages globus pallidus → death

Clinical Features of Parkinson's disease

Hypokinetic Movements Akinesia and Bradykinesia Decreased associated movement: no swinging of arms during walking Masklike face: no facial expression during speaking. Hyperkinetic Movements Rigidity: Motor neuron discharge is ↑ed in both agonists & antagonists. Lead pipe rigidity; sometimes cogwheel rigidity is also seen. Posture is that of flexion attitude. Tremor: Pill-rolling tremors (rhythmic contraction of thumb over first two fingers @ 6-8 times/sec) Present at rest but disappears during activity (resting or static tremor). Festinant Gait (shuffling gait): Patient is bent forward (Stooped), & walks quickly with short steps as if trying to catch up center of gravity or preventing himself from falling down. If he is suddenly pulled backwards, he begins to walk backwards & is unable to stop himself (retropulsion). Tendon jerks: more difficult to elicit due to rigidity

Autonomic Responses of limbic system

Hypothalamus is called head ganglion of ANS for its major role in autonomic functions. Insular & prefrontal areas of cortex are involved in regulation of ANS. Autonomic component of emotional response are controlled by amygdala. Parts of limbic system that project to brainstem & spinal cord centers have major influence on autonomic functions.

Cause of Parkinson's Disease

Idiopathic Drugs: Reserpine (reduce dopamine stores in appropriate nerve endings); Phenothiazine (blocks D2 dopamine receptor in neostriatum) MPP: Methyl-phenyl-tetrahydropyridinum (MPTP), found in contaminated low quality street heroine, is converted by MAO-B into methyl-phenyl-pyridinum (MPP), which accumulates in dopaminergic neurons of basal ganglia & destroy them. Exposure to certain toxins (eg, manganese dust, carbon disulfide) and severe carbon monoxide poisoning may lead to parkinsonism.

Gerstmann Syndrome

If the lesion is confined to just the angular gyrus (area 39) , the result is a loss of ability to comprehend written language (alexia) and to write it (agraphia), but spoken language may be understood. Alexia with agraphia in pure angular gyrus lesions is often seen with 3 other unique symptoms: acalculia (loss of the ability to perform simple arithmetic problems), finger agnosia (inability to recognize one's fingers) , and right-left disorientation.

Aphasias

Impaired or absent communication by speech, writing, or signs (i.e., loss of the capacity for spoken language). Results from lesions in the dominant hemisphere.

Amnesia

Impairment of memory. Two types: Retrograde amnesia: loss of memory for events that just precede the head injury or the disease . Usually loss occurs only for short term memory. Commonly occurs in head injury. Anterograde amnesia: inability to recall the memory or to form new memories after the event (head injury, mental shock or disease).

Aphasias

Impairments of the ability to use or understand language that usually results from brain damage

Non-declarative memory

Implicit Information can not be recalled consciously Types of non-declarative memory: Priming: facilitation of recognition of words or objects by prior exposure to them Procedural memory: ability to learn a skill or procedure (e.g., riding a bicycle) Learned emotion: ability to form emotional associations in memory Conditioned reflexes: Eg., hearing a lunch time alarm → induce reflex GI activity

Motor and Sensory homunculus

Indicates that the upper limb and head are demonstrated on the lateral surface of the cortex. The pelvis and the lower limb are represented on the medial surface of the hemispheres. Therefore, the motor and sensory functions of the lower limb are supplied by the anterior cerebral artery while the motor and sensory functions of the upper limb and head are supplied by the middle cerebral artery.

Fever

Infections cause cells of the immune system to secrete cytokines, which cross the blood-brain barrier at the organum vasculosum laminae terminalis (OVLT). Endothelial cells of the OVLT produce prostaglandin E2 (PGE2) in response to cytokines, resulting in an increase in the hypothalamic set point for body temperature. The phases of fever. Changes in the hypothalamic set point during episodes of fever induce effector responses that cause the measured body temperature to change. At the beginning of a fever, the body temperature is initially below the set point; the patient feels cold and experiences "chills" (vasoconstriction and possible shivering) until the fever is established. When a fever "breaks," the body temperature is suddenly above the set point temperature; the patient feels hot and experiences vasodilation and sweating until the body cools.

Basket Cells

Inhibitory interneurons in the cerebellar cortex whose cell bodies are located within the Purkinje cell layer and whose axons make basketlike terminal around Purkinje cell bodies

connections of basal ganglia

Inputs Arrive at the Striatum Outputs Arise from the Internal Globus Pallidus and the Substantia Nigra Pars Reticulata

Spinocerebellum

Intermediate in development (paleocerebellum). Called spinocerebellum as it receives proprioceptive & other sensory inputs from all the body parts through spinal cord. Also receives inputs from motor cortex, where motor planning is carried out. Smoothes & coordinates movement by comparing plan with movement. Two regions: Vermis & Paravermis Vermis: Projects to brainstem nuclei that control axial & proximal limb muscles. Controls posture. Paravermis: Projects to brainstem nuclei that control distal limb muscles. Skilled voluntary movements.

Limbic System

Involved in emotion, memory, attention, feeding, and mating behaviors. It consists of a core of cortical and diencephalic structures found on the medial aspect of the hemisphere. Limbic system comprises Limbic lobe of the cortex Subcortical Structures associated with it.

Pathology of Alzheimer's

Involves defective degradation of amyloid precursor protein, leading to β-amyloid plaques, and hyperphosphorylated tau protein, leading to neurofibrillary tangles. Macroscopically, the brain is atrophic, particularly the cerebral cortex and hippocampus. Histology reveals the presence of senile plaques and neurofibrillary tangles in the cerebral cortex. Histochemical staining demonstrates significant quantities of amyloid in plaques. Many different neurotransmitter abnormalities have been described, in particular impairment of cholinergic transmission, although noradrenaline, 5-HT, glutamate and substance P are also involved

Transcortical motor aphasia

Involves good comprehension, good repetition, and nonfluent speech.

Wernicke-Korsakoff disease

Is often found in chronic alcohol abuse. Acute CNS changes due to thiamine deficiency are called Wernicke's encephalopathy. These findings of confusion, ataxia, nystagmus, and ophthalmoplegia are reversible. However, chronic, irreversible CNS changes due to thiamine deficiency such as retrograde and anterograde memory impairment, as well as confabulation, are called Korsakoff's psychosis. Petechial hemorrhage and infarction often are seen in the mammillary bodies, thalamus, and periaqueductal gray matter, the limbic system is also affected in Korsakoff psychosis. The deficiency can arise as a result of malnutrition (particularly when due to chronic alcohol misuse), malabsorption or even protracted vomiting (as in hyperemesis gravidarum). Treatment consists of intravenous thiamin (in the form of Pabrinex, 2 vials 8-hourly for 48 hours) initially, followed by oral (100 mg 8-hourly), in addition to treating the underlying cause.

Sensitization

Is the opposite if habituation and refers to increased responses, with both types of change resulting from previous experience.

Indirect pathway of basal ganglia

It begins with the Striatum being excited by the Cortex (just like the direct pathway). Then Striatal neurons send inhibitory input to the external segment of the Globus Pallidus using the neurotransmitters GABA or Enkephalin. The Globus Pallidus external segment usually sends inhibitory input to the Subthalamic Nucleus using GABA, but if it is inhibited by the Striatum then it is unable to inhibit the Subthalamic nucleus leaving it free to fire. The Subthalamic Nucleus being uninhibited sends the only purely excitatory (Glutamate)input within the Basal Ganglia pathways to the Globus Pallidus internal segment and the Substantia Nigra pars reticulata. These structures then inhibit the VA and VL of the Thalamus making it unable to send excitatory input to the Cortex and thus indirectly inhibiting the Motor Cortices, which inhibits movement. Cholinergic neurons found within the striatum have the opposite effect. Acetylcholine (Ach)drives the indirect pathway, decreasing cortical excitation.

Direct pathway of basal ganglia

It begins with the Striatum being excited by the Cortex. The Striatum then inhibits the internal segment of the Globus Pallidus and the Substantia Nigra pars reticulata using the neurotransmitters GABA or Substance P (Sub P). When these structures are inhibited they cannot inhibit the Thalamus rendering it free to fire and send excitatory input up to the Cortex, which facilitates movement.

Arcuate fasciculus

It connects these two areas of the cortex (Broca and Wernicke). We want to produce words (Broca) that make sense (Wernicke) and, similarly, understand language input and respond. The arcuate fasciculus is thought to be a connection that monitors speech and facilitates the repetition of words.

Gerstmann Syndrome

It is a cognitive impairment that results from damage to a specific area of the brain, the left parietal lobe in the region of the angular gyrus. It may occur after a stroke or in association with damage to the parietal lobe. It is characterized by four primary symptoms: a writing disability (agraphia or dysgraphia), a lack of understanding of the rules for calculation or arithmetic (acalculia or dyscalculia), an inability to distinguish right from left, and an inability to identify fingers (finger agnosia).

Alzheimer Disease

It is a progressive, degenerative and ultimately fatal brain disease, in which cell to cell connections in the brain are lost. It is the most common form of dementia, and is generally diagnosed in patients over the age of about 65. Most cases are sporadic. About 10% of cases genetic basis, usually associated with genes on chromosome 1, 14, 19, or 21. Amyloid precursor protein (APP) and apolipoprotein E4 (APOE4) genes are important in familial forms. It is clinically distinguished by the presence/absence of focal neurologic deficits. The most commonly recognized symptom is an inability to acquire new memories and difficulty in recalling recently observed facts, but it is by no means the only symptoms. Loss of short-term memory is followed by confusion, irritability and aggression, mood swings, language breakdown, long-term memory loss, and ultimately a gradual loss of bodily functions and death. This differs from Pick's disease in frontotemporal versus diffuse cortical atrophy.

Parkinson's Disease (Paralysis Agitans)

It is a sporadic disorder of unknown etiology that occurs worldwide. The usual age of onset is between 40 and 70 years. Agitans means shaking, hence, also called shaking palsy. It usually have the classic triad of Resting tremor, bradykinesia, and lead pipe/cogwheel rigidity, accompanied by postural instability that causes an unsteady gait.

Athetosis

It is characterized by writhing, twisting movements of the limbs, face, and trunk that sometimes merge with faster choreic movements, giving rise to the term choreoathetosis. Important causes include perinatal hypoxia involving the basal ganglia, kernicterus caused by severe neonatal jaundice, Wilson's disease, ataxia, telangiectasia, Huntington's disease, and antipsychotic or anti-emetic medications.

Sagittal sinus thrombosis

It is often associated with one of the hypercoagulable states. It occurs with increased frequency in pregnant women and within the first few weeks post partum. Obstruction of venous drainage usually causes elevated intracranial pressure. Back pressure in cortical veins can cause parasagittal hemorrhages. In addition, the increased venous pressure can decrease cerebral perfusion, leading to infarcts. Seizures are common. Patients often have headaches and papilledema, and they may have depressed level of consciousness. More subtle radiological signs of sagittal sinus thrombosus include increased density of the sagittal sinus on CT due to coagulated blood, or increased signal on MRI. In suspected sagittal sinus thrombosus, regardless of whether these subtle radiological findings are present, a more definitive study should be performed, such as magnetic resonance venography (MRV) or a conventional angiogram. Treatment usually involves anticoagulation therapy, although this is controversial when hemorrhage has occurred. Seizures and elevated intracranial pressure should be treated as well, when present. Venous thrombosis can also occur less commonly in other intracranial venous sinuses, in the deep cerebral veins, or in a major cortical vein, leading to infarcts or hemorrhage in the territories of these vessels.It is often associated with one of the hypercoagulable states.

Cerebrum

It is the largest part of the forebrain. It is highly developed in human. It is derived from the telencephalon. Each hemisphere has a covering of gray matter, the cortex and internal masses of gray matter, the basal nuclei, and a lateral ventricle. They are connected by the corpus callosum. Consists of the neocortex (90%) and the allocortex (10%). Neocortex (isocortex) a six-layered cortex. Allocortex (heterogenetic) three-layered and includes two types: 1. Archicortex: includes the hippocampus and the dentate gyrus. 2. Paleocortex: includes the olfactory cortex.

Chorea

It means literally "dance" and is applied to movement disorders characterized nearly continuous involuntary movements that have a fluid or jerky, constantly varying quality. In mild cases, low-amplitude chorea may be mistaken for fidgeting or restless movements of the extremities, face, or trunk. Choreic movements are often incorporated into voluntary movements in an attempt to conceal their occurrence. In severe cases, larger-amplitude movements resemble frantic "break dancing," occurring constantly, interrupting voluntary movements, and increasing during distraction or during ambulation. Chorea can involve proximal and distal extremities, the trunk, neck, face, and respiratory muscles.

Thalamic Syndrome

It occurs due to lesion of thalamus, usually after the thalamogeniculate artery is blocked. It results in temporary contralateral hemi anesthesia with ataxia due to loss of position sense from the limbs Later, the patient may complaint of agonizing pain called thalamic pain on affected side. The threshold to the pain is raised but the reaction to pain is exaggerated. It is usually seen in the patient is recovering from a thalamic infarct.

Thalamus

Largest division of the diencephalon. Receives precortical input from all sensory systems except the olfactory system. Largest input received from the cerebral cortex. Projects primarily to the cerebral cortex and to a lesser degree to the basal nuclei and hypothalamus. Plays an important role in sensory and motor system integration. The major nuclear divisions of the thalamus, the thalamic nuclei, include anterior, medial, and lateral nuclei

nuclei of Hypothalamus

Lateral- induces hunger Ventromedial- satiety Anterior- cooling Posterior- heating Suprachiasmatic- circadian rhythm Arcuate- hunger + dopamine-inhibiting Lateral pre-optic- sleep/wake Medial pre-optic- LH/FSH, sexually dymorphic

Layers of cerebral cortex

Layer I the molecular layer: is the outermost layer of the cerebral cortex and consists primarily of horizontally running nerve fibers. Layer II, the external granular layer: is made of densely packed granule cells with dendrites extending into molecular layer and axon passing deeper layers. Axons of these neurons from association projections that interconnect different parts of hemisphere. Layer III, the external pyramidal layer: it consist of moderate sized pyramidal cells. Axons of these neurons from commissural projections that interconnect the 2 hemispheres via the corpus callosum. Layers IV, the internal granular layer: consist mostly of small stellate cells. It represents the major sites of termination of ascending cortical inputs from the thalamus. Layers V internal pyramidal layers: contains medium to large pyramidal cells. Betz cells, the largest neurons in the CNS, are found in layer V of the primary motor cortex, which is located on the precentral gyrus. Layer VI the multiform layer: consist of pyramidal and fusiform cells.

Cerebellum

Literally means "Little brain". Receives inputs of almost all sensory modalities Proprioceptive inputs from spinal cord Special sensory inputs from visual, auditory, & vestibular structures. Fibers from cerebellum project to all areas of brain involved in control of motor activities. Plays critical role in motor control by integrating sensory & motor information in brain. Strongly influences all aspects of movement starting from rate, range, force, & direction to termination of movement. Also regulates vestibulo-ocular reflexes & motor learning.

Cerebellar organization

Located in posterior cranial fossa, behind the brainstem. Connections with brainstem Superior cerebellar peduncle - midbrain Middle cerebellar peduncle - pons Inferior cerebellar peduncle - medulla Surface area: about 75% of cerebral cortex Weight: only 10% of cerebrum Two main fissures divides cerebellum into two major parts: Primary fissure - separates anterior from posterior lobe Posterolateral fissure - separates flocculonodular lobe from rest

Factors affecting Memory consolidation

Many factors can influence this transfer, including: ■ Emotional state. We learn best when we are alert, motivated, surprised, and aroused. Norepinephrine, a neurotransmitter involved in memory processing of emotionally charged events, ■ Rehearsal. Rehearsing or repeating the material enhances memory. ■ Association. Tying "new" information to "old" information already stored in LTM appears to be important in remembering facts. ■ Automatic memory. Not all impressions that become part of LTM are consciously formed. Memories transferred to LTM take time to become permanent. The process of memory consolidation apparently involves fitting new facts into the categories of knowledge already stored in the cerebral cortex.

Feeding, Obesity, and Emaciation

Marked increases in appetite occur as a result of lesions of the ventromedial hypothalamus. This is associated with significant weight gain and striking changes in emotional behavior (usually characterized by expressions of rage). Lesions of the lateral hypothalamus, on the other hand, result in loss of appetite and emaciation.

Hypothalamic sleep disorders

May result from damage (such as from encephalitis) to the posterior region of the hypothalamus (i.e., the diencephalic-midbrain juncture). The result is prolonged periods of sleep. The effects may be due to damage to ascending fibers from the reticular

Semantic memory

Memory of the meanings of words-the kind of memory that lets us recall not only the names of the world's great capitals, but also social customs, the functions of things, and their color and odor.

Blood supply of the cerebrum

Middle cerebral artery (MCA) supplies: The lateral surface of the frontal, parietal, and upper temporal lobes The posterior limb and genu of the internal capsule Most of the basal ganglia Anterior cerebral artery (ACA) Supplies: 1. Medial surface of frontal and parietal lobes 2. Anterior four-fifths of corpus callosum· 3. Anterior limb of internal capsule Posterior cerebral artery (PCA) Supplies: 1. Occipital lobe 2. Lower temporal lobe 3. Splenium 4. Mid brain

Major afferents to the cerebellum

Mossy fibers and Climbing Fibers

Disorders of Basal Ganglia

Movements disorders Bradykinesia- slowed movements Hypokinesia -decreased amount of movements. Akinesia -absence of movement." These terms are traditionally reserved for localizations at levels higher than the upper motor neurons. Rigidity Increased resistance to passive movement of a limb is called rigidity. It is often present in disorders that cause bradykinesia or dystonia. Rigidity caused by basal ganglia disorders tends to be more continuous throughout attempts to bend the limb, and it has therefore been called plastic,waxy, or lead pipe rigidity. Dystonia The patient assumes abnormal, often distorted positions of the limbs, trunk, or face that are more sustained or slower than in athetosis. It can be generalized, unilateral, or focal. Focal dystonias include torticollis, which involves the neck muscles; blepharospasm, which involves the facial muscles around the eyes; spasmodic dysphonia, which involves the laryngeal muscles; and writer's cramp. These disorders are presumed to be caused by basal ganglia dysfunction, although usually no focal lesion is found. Many cases of dystonia respond well to injection of small amounts of botulinum toxin("Botox") into the affected muscles, which needs to be repeated every few months.

Ballism

Movements of the proximal limb muscles with a larger-amplitude, more rotatory or flinging quality than chorea are referred to as ballism or ballismus. The most common type is hemiballismus, in which there are unilateral flinging movements of the extremities contralateral to a lesion in the basal ganglia. The classic cause is a lacunar infarct of the subthalamic nucleus, which leads to decreased pallidal inhibition of the thalamus

Cerebrocerebellum

Newest phylogenetically (neocerebellum). Called cerebrocerebellum for its connections with the cortex. Cortex projects to neocerebellum via pontine nuclei; hence, also called corticopontocerebellum. Involved in planning & programming of the movements as it interacts with the cortex.

The Dominant Hemisphere

Ninety five percent of human population is right handed and has speech and language functions localized in the left or dominant hemisphere and responsible for propositional language (grammar, syntax, semantic) speech and calculation. The right hemisphere is usually non dominant and responsible for 3 dimensional or spatial perception or nonverbal ideation. Most left-handed people show language functions bilaterally, although a few, with strong left-handed preferences, show right-sided speech and language functions. The cerebral dominance is determined by Wada Test. Sodium amobarbital (Amytal) is injected in carotid artery. If patient becomes aphasic, the anesthetic was administered to the dominant hemisphere.

Bruxism

Nocturnal grinding of teeth Usually associated with dreams in REM sleep.

Dysprosodies

Nondominant hemispheric language deficits that affect the emotionality of speech (inflection, melody, emphasis, and gesturing).

Anxiety

Normal emotional reaction to a stimulus in which there is uncertainty or doubt about future & apprehension for unknown. Center of anxiety: frontal part of temporal lobe. α2-GABAA receptors have been identified to mediate anxiety. Benzodiazepine act by increasing chloride conductance in the receptors.

Pathological Features of Parkinson's disease

Pathologically, there is loss of pigmented dopaminergic neurons in the substantia nigra pars compacta, causing the substantia nigra to appear pale to the eye on cross section. Remaining dopaminergic neurons often contain characteristic cytoplasmic inclusions called Lewy bodies, which are eosinophilic, contain ubiquitin and α-synuclein, and have a faint halo.

Hypersomnia

Patient sleeps for days to weeks continuously. Due to damage to brainstem RAS or neurons in subthalamus or hypothalamus

Vestibulocerebellum

Phylogenetically oldest part (achicerebellum). Called vestibulocerebellum for its extensive & reciprocal connections with the vestibular nuclei Concerned with equilibrium & learning induced changes in vestibulo-ocular reflex.

Functions of basal ganglia

Planning & Programming of movements by preventing oscillations Subthalamic nuclei provide excitatory input to globus pallidus Globus pallidus sends fibers back to subthalamic nuclei Activity of basal ganglia is more during slow, steady damp movement & is silent during, rapid, saccadic movement. Inhibits the stretch reflex (muscle tone) by stimulation of inhibitory motor cortex and Inhibitory reticular formation Neostriatum regulates subconscious gross movements occurring in groups of the muscles. Caudate nucelus plays important role in cognitive processes because of its interconnections with orbitofrontal & dorsolateral prefrontal lobe. Globus pallidus provides appropriate muscle tone for performance of skilled movements. Substantia nigra is center for coordination of impulses essential for skilled movements. Control of normal automatic & associated movements such as swinging of arms during walking (initiated by motor cortex area 6).

Caudate nucleus

Plays important role in cognitive processes because of its interconnections with orbitofrontal & dorsolateral prefrontal lobe.

Blood supply to the thalamus

Posterior cerebral [thalamogeniculate + thalamoperforating] arteries Posterior Choroidal Artery

Fastigial Nucleus

Present in deep vermal portion Vermal cortical portion of spinocerebellum projects here.

Dentate Nucleus

Present in hemispheric portion Inputs from neocerebellum

Temporal Lobe

Primary auditory cortex On its superior and lateral aspect, the temporal lobe contains the primary auditory cortex. Auditory cortex (areas 41 and 42) is located on the 2 transverse gyri of Heschl, which cross the superior temporal lobe deep within the lateral sulcus. Much of the remaining superior temporal gyrus is occupied by area 22 auditory association cortex, which receives a considerable projection from both areas 41 and 42 and projects widely to both parietal and occipital cortices. Patients with unilateral damage to the primary auditory cortex show little loss of auditory sensitivity but have some difficulty in localizing sounds in the contralateral sound field. Area 22 is a component of Wernicke area in the dominant hemisphere, and lesions here produce a Wernicke aphasia.

Parietal Lobe

Primary somatosensory cortex The postcentral gyrus corresponds to Brodmann areas 3, l, and 2 and contains primary somatosensory cortex. There is a similar somatotopic representation of the body here, with head, neck, upper limb, and trunk represented on the lateral aspect of the hemisphere, and pelvis and lower limb represented medially. These areas are concerned with discriminative touch, vibration, position sense, pain, and temperature. Lesions in somatosensory cortex result in impairment of all somatic sensations on the opposite side of the body, including the face and scalp. Posterior parietal association cortex Just posterior and ventral to the somatosensory areas is the posterior parietal association cortex, including Brodmann areas 5 and 7. Wernicke area The inferior part of the parietal lobe and adjacent part of the temporal lobe in the dominant (left) hemisphere, known as Wernicke area, are cortical regions that function in language comprehension. At a minimum, Wernicke area consists of area 22 in the temporal lobe but may also include areas 39 and 40 in the parietal lobe. Areas 39 (the angular gyrus) and 40 (the supramarginal gyrus) are regions of convergence of visual, auditory, and somatosensory information.

Wilson's disease

Progressive hepatolenticular degeneration It results from an abnormality of copper metabolism, causing the accumulation of copper in the liver and basal ganglia. Feature Characterized by personality changes, tremor, dystonia, and athetoid movements. A thin brown ring a round the outer cornea, the Kayser-Fleischer ring, may be present and aid in the diagnosis. Low plasma ceruloplasmin (plasma copper binding protein) → increase copper content in substantia nigra. Severe degeneration of lentiform nucleus with cirrhosis of liver.

Globus pallidus

Provides appropriate muscle tone for performance of skilled movements.

Rage & Placidity

Rage: anger reaction in which person looses temper in response to a minor stimulus. Placidity: emotional state in which the person is not disturbed even in response to a major irritating stimulus. Destruction of neocortex, ventromedian hypothalamus, & septal nuclei results in rage in response to a minor stimulus. Bilateral lesions of amygdaloid nuclei lead to greater placidity.

Habituation

Refers to decreases in responses by repeated presentation of a known stimulus

Neostriatum

Regulates subconscious gross movements occurring in groups of the muscles.

Regulatory functions of hypothalamus

Regulation of body's internal environment, Regulation of water balance Regulation of body temperature Regulation of food intake (feeding behavior) Regulation of sleep and wakefulness

Treatment for Parkinson's disease

Replacement of dopamine: Dopamine cannot cross blood brain barrier. Levo-DOPA, a precursor of dopamine, that easily crosses BBB is the drug of choice. Dopamine agonists - e.g., Bromocriptine are also used. Anticholinergics: Alteration in the ratio of dopamine & acetylcholine plays an important role in Parkinson's disease. Injection of Anticholinergics → ↓es Ach concentration in basal ganglia → reestablishes Ach - dopamine ratio → improves the symptoms Selegilin (Deprenyl): Inhibits MAO-B & prevents formation of MPP from MPTP. Amantadine: Antiviral medication is also effective in treating Parkinson's disease due to its anticholinergic and antiglutamatergic effects and also acts by increasing dopamine output from intact nerve terminals. COMT (catechol-O-methyl transferase) Inhibitor: This enzyme is involved in degrading neurotransmitters. e.g. Entacapone, tolcapone, and nitecapone

Wernicke's aphasia

Results from a lesion in the sensory speech region, i.e., in the posterior portion of the temporal gyrus of the auditory association cortex (area 22) and/or the supramarginal gyrus (area 40). Language comprehension is impaired in these patients. They also lose the ability to repeat words spoken by somebody else. Spontaneous speech is fluent; sometimes patients speak all the time (logorrhea). However, in doing so they may make occasional phonetic ("spill" instead of "spin") or semantic errors ("mother" instead of "woman" [ paraphasia]) or create new words (neologisms).

Expressive dysprosody

Results from a lesion that corresponds to the broca area but is located in the nondominant hemisphere. ● Patients cannot express emotion or inflection in their speech.

Receptive dysprosody

Results from a lesion that corresponds to the wernicke area but is located in the nondominant hemisphere. ● Patients cannot comprehend the emotionality or inflection in the speech they hear.

Genetic factors for Parkinson's disease

SNCA (synuclein, alpha non A4 component of amyloid precursor): SNCA makes the protein alpha-synuclein. In brain cells of individuals with Parkinson's disease, this protein aggregates in clumps called Lewy bodies. Mutations in the SNCA gene are found in early-onset Parkinson's disease. PARK2 (Parkinson's disease autosomal recessive, juvenile 2): The PARK2 gene makes the protein parkin. Mutations of the PARK2 gene are mostly found in individuals with juvenile Parkinson's disease. Parkin normally helps cells break down and recycle proteins. PARK7 (Parkinson's disease autosomal recessive, early onset 7): PARK7 mutations are found in early-onset Parkinson's disease. The PARK7 gene makes the DJ-1 protein, which may protect cells from oxidative stress. PINK1 (PTEN-induced putative kinase 1): Mutations of this gene are found in early-onset Parkinson's disease. The exact function of the protein made by PINK1 is not known, but it may protect structures within the cell called mitochondria from stress. LRRK2 (leucine-rich repeat kinase 2): LRRK2 makes the protein dardarin. Mutations in the LRRK2 gene have been linked to late-onset Parkinson's disease.

Sexual Activity

Sexual reflexes are coordinated mainly in spinal cord & brainstem. Sexual behavior is controlled mainly by the limbic system & higher cortical centers override limbic influences & refine the behavior. In males: Lesion of neocortex inhibits sexual behavior. Bilateral lesion of limbic system & destruction of amygdala result in intense sexual activity ( hypersexuality). In females: Lesion of anterior hypothalamus abolishes sexual activity in animals.

Sleep architecture

Sleep consist of two distinct states NREM and REM Pattern of NREM and REM in a 90 to 110 minute cycle

Sleep cycle

Sleep is divided into 90-minute cycles of rapid eye movement (REM) and non-rapid eye movement (NREM) sleep; these 90-minute cycles are repeated three to six times during the night. The time between the onset of sleep and the end of the first REM period defines the first sleep cycle. After that, sleep cycles (i.e., second through sixth cycle) always start with NREM sleep and end in REM sleep. The majority of slow-wave sleep (SWS) occurs in the first third of the night, while the majority of REM (and most dreams) occurs in the last third of the night. The National Sleep Foundation recommends that adults aged 26-64 sleep 7 to 9 hours per night, and adults aged 65 and older sleep 7-8 hours per night.

Parasomnic disorders

Somnolescent motor starts: certain jerky motor activities due to excitation of motor centers Sensory Paroxysms: sudden flash of light or crashing sound, or sensation of turning or lifting of the body are experienced Nocturnal Paroxysmal Dystonia: choreoathetotic or ballistic dystonic movements that occur in NREM sleep. Sleep paralysis: unable to activate muscles towards end of REM sleep. Night terrors & Nightmares: usually in children in stage 3 or 4 of NREM sleep Somnambulism: sleep walks with open eyes in stage 4 of slow wave sleep REM Sleep behavior disorders: become aggressive, angry, & shout loudly or even become violent & cause injury to themselves or to bedmate during REM phase.

Stage IV Sleep

Stage of deep sleep EEG Patterns: delta rhythm predominant over the whole scalp. Maximum time of sleep is spent in this stage initial stage of sleep. Hardest to arouse

Stage III Sleep

Stage of moderately deep sleep. EEG Patterns: lower frequency & higher amplitude.

Dementia

Syndrome consisting of several intellectual inabilities. The deficits occurs for many cognitive functions including learning and memory. Senile dementia, Alzheimer's disease.

Connections of limbic system

System is interconnected with anterior and dorsomedial nuclei of the thalamus and the mammillary bodies. The cingulate gyrus is the main limbic cortical area. Limbic-related structures also project to wide areas of the prefrontal cortex. Central projections of olfactory structures reach parts of the temporal lobe and the amygdala. Receives inputs from sensory systems, including the cerebral cortex, and monoamine neuronal groups of the brainstem reticular formation. Primary outputs of the limbic system are directed to the hypothalamus. This arrangement allows the limbic system to alter the activity of the hypothalamus in response to sensory input. The hypothalamus provides the integrating mechanism for different forms of emotional behaviors as well as visceral and autonomic responses, the limbic system serves as a key modulating region of these processes by virtue of its inputs to the hypothalamus. Inputs to the limbic system from monoamine pathways can provide the substrates underlying mood changes. PAG, periaqueductal gray matter.

Avoidance System

System that produce feeling of displeasure. Structures: lateral portion of posterior hypothalamus, dorsal midbrain & entorhinal cortex. Stimulation of these areas - feelings ranges from fear to terror. Also called punishment system.

Reward System

System that produce feeling of pleasure. Mainly consists of dopaminergic pathways from ventral tegmentum to nucelus accumbens. Frontal cortex & hypothalamus also belong to this system. Nucleus accumbens is major reward center in which dopamine is major neurotransmitter

Functions of hypothalamus

TAN HATS: Thirst/water balance Adenohypophysis control Neurohypophysis control Hunger Autonomic regulation Temperature regulation Sexual urges Mainly responsible for maintaining homeostasis Main functions of hypothalamus are divided into following categories: Regulatory functions Endocrinal functions Autonomic functions

Cerebellar Function Tests

Test for coordination: finger-nose test; knee-heel (heel- shin)test Test for postural stability: stand erect with feet closed but eyes open Assessment of gait & speech Assessment of various aspects of ataxia

Sensory Loss

Thalamic lesion resulting from thrombosis or hemorrhage of one of the arteries supplying the thalamus and damage to the ventral posteromedial nucleus and the ventral posterolateral nucleus will result in the loss of all forms of sensation, including light touch, tactile localization and discrimination, and muscle joint sense from the opposite side of the body. The thalamus is centrally located among other important nervous structures. Usually, a thalamic lesion results in dysfunction of neighboring structures, producing symptoms and signs that overshadow those produced by the thalamic disease. For example, a vascular lesion of the thalamus may also involve the midbrain, with resulting coma, or a lateral extension of thalamic disease may involve the internal capsule and produce extensive motor and sensory deficits.

Intrinsic organization of the cerebral cortex

Thalamocortical and intracortical projections terminate mainly in layer IV, and monoaminergic projections are distributed mainly to more superficial layers. Cortical afferents terminating in layer IV can either excite or inhibit pyramidal cells in layer V, which contribute significantly to the outputs of the cerebral cortex. The major outputs to the spinal cord, cranial nerve motor nuclei, other brainstem structures, thalamus, and neostriatum arise in layers V-VI, whereas projections to other regions of cortex either on the ipsilateral or contralateral side arise from layer III.

Reticular Activating System (RAS)

The RAS is inhibited by sleep centers located in the hypothalamus and other neural regions, and is depressed by alcohol, sleep inducing drugs, and tranquilizers. Severe injury to this system, as might follow a knockout punch that twists the brain stem, results in permanent unconsciousness (irreversible coma). Although the RAS is central to wakefulness, some of its nuclei are also involved in sleep.

Memory

The ability to retain and recall learned information & experiences. Two general types of memory 1. Explicit or Declarative memory 2. Implicit or Non-declarative memory

Reticular Formation Components

The ascending portion of the reticular formation is called the reticular activating system (RAS),which consists of sensory axons that project to the cerebral cortex, both directly and through the thalamus. Groups of neurons shown in orange project to thalamus, & enhance arousal of cerebral cortex to sensory information relayed from thalamus. Groups of neurons shown in red project to cerebral cortex & more directly arouse the cerebral cortex to ascending sensory information. Activation of RAS promotes wakefulness, & inhibition of RAS promotes sleep. Also has a motor arm. Some of its motor nuclei project to motor neurons in the spinal cord via the reticulospinal tracts, and help control skeletal muscles during coarse limb movements.

Benefits of Fever

The benefit of fever to the organism is uncertain. It is presumably beneficial because it has evolved and persisted as a response to infections and other diseases. Many microorganisms grow best within a relatively narrow temperature range and a rise in temperature inhibits their growth. In addition, antibody production is increased when body temperature is elevated. Hyperthermia benefits individuals infected with anthrax, pneumococcal pneumonia, leprosy, and various fungal, rickettsial, and viral diseases. Hyperthermia also slows the growth of some tumors. However, very high temperatures are harmful. A rectal temperature over 41°C (106°F) for prolonged periods results in some permanent brain damage. When the temperature is over 43 °C, heat stroke develops and death is common.

Reticular Formation

The broad region where white matter and gray matter exhibit a netlike arrangement is known as the reticular formation. It extends from the superior part of the spinal cord, throughout the brain stem, and into the inferior part of the diencephalon. Neurons within the reticular formation have both ascending (sensory) and descending (motor) functions. Characteristically, theses neurons have Long ascending branches projecting to thalamus, hypothalamus, & cortex. Long descending branches projecting to the spinal cord.

Neurons and fibers of the cerebellum

The cerebellar granule cells are widely held to be the most abundant class of neurons in the human brain. The parallel fibers bifurcate in the molecular layer to form T-shaped branches that relay information via excitatory synapses onto the dendritic spines of the Purkinje cells.

Conductive aphasia

The connection between sensory and motor speech center (arcuate fasciculus) is interrupted. Speech is fluent (although sometimes paraphasic) and comprehension is good. However, their repetition ability is greatly impaired. They are also unable to read aloud, even though they understand the text they read.

Memory consolidation

The conversion of short-term memory into a long-term memory and is enhanced by repetition and by adding several sensory modalities (e.g., writing out lecture notes) or adding emotional context. Requires the hippocampus, The hippocampus can access widespread areas of the cortex for memory storage via the nearby parahippocampal cortex and other parts of the temporal lobe. The ability to recall long-term memories that are already stored does not require the hippocampus.

Fibers of the Cerebrum

The gray matter on the outer surface of the cerebrum is the cortex, and clusters of gray matter deep inside the brain are nuclei. The white matter of the brain between the cortex and nuclei is the cerebral medulla. The cerebral medulla consists of nerve tracts that connect the cerebral cortex to other areas of cortex or other parts of the CNS. These tracts fall into three main categories: (1) Association fibers, which connect areas of the cerebral cortex within the same hemisphere; (2) Commissural fibers, which connect one cerebral hemisphere to the other; and (3) Projection fibers, which are between the cerebrum and other parts of the brain and spinal cord.

Ideational apraxia

The inability to demonstrate the use of real objects (e.g., Smoke a pipe [a multistep complex sequence]). ● A misuse of objects owing to a disturbance of identification (agnosia). ● Results from a lesion in the wernicke area.

Construction apraxia

The inability to draw or construct a geometric figure (e.g., The face of a clock). Called hemineglect if the patient draws only the right half of the clock. The lesion is located in the right inferior parietal lobule.

Apraxia

The inability to perform motor activities in the presence of intact motor and sensory systems and normal comprehension.

Medial and Lateral zones of hypothalamus

The lateral zone of the hypothalamus refers to one of three zones of the hypothalamus when it is subdivided by planes parallel to the midline. The others are the periventricular zone of the hypothalamus and the medial zone of the hypothalamus. The lateral zone includes the lateral preoptic area and the lateral hypothalamic area The medial zone lies between the laterral and periventricular. It includes the paraventricular nucleus of the hypothalamus, the supraoptic nucleus, the medial preoptic nucleus, the anterior nucleus of the hypothalamus, the retrochiasmatic area, the ventromedial nucleus of the hypothalamus, the dorsomedial nucleus of the hypothalamus, the supramammillary nucleus, the medial part of the medial mammillary nucleus, the lateral part of the medial mammillary nucleus and the lateral mammillary nucleus

Functional Anatomy of limbic system

The limbic lobe comprises a ring of cortex on the medial surface of the brain, which spans across aspects of the frontal, parietal, and temporal lobes. It consists of the parahippocampal gyrus, the cingulate gyrus, and a continuation of the cingulate gyrus anteriorly and inferiorly, called the subcallosal gyrus. These cortical areas are interconnected by a subcortical fiber bundle called the cingulum. The major subcortical structures of the limbic system include the hippocampus (major role in learning and memory), the amygdala or amygdaloid nuclear complex (major role in emotions and drives), and the septal nuclei (associated with reward mechanisms).

Ideomotor apraxia

The loss of the ability to perform intransitive or imaginary gestures, resulting in the inability to perform complicated motor tasks (e.g., Saluting, blowing a kiss, or making the v-for-peace sign). ● May be typified by facial apraxia, which is also known as buccofacial or facial-oral apraxia, the most common type of apraxia. ● Results from a lesion in the wernicke area.

Short-term memory (STM)

The memory system in which information is held for brief periods of time while being used Also called working memory,is the preliminary step.

Occipital Lobe

The occipital lobe is essential for the reception and recognition of visual stimuli and contains primary visual and visual association cortex. Visual cortex The visual cortex is divided into striate (area17) and extrastriate (areas18 and 19). Area 17, also referred to as the primary visual cortex, lies on the medial portion of the occipital lobe on either side of the calcarine sulcus. Its major thalamic input is from the lateral geniculate nucleus. Visual association cortex Anterior to the primary visual or striate cortex are extensive areas of visual association cortex. Visual association cortex is distributed throughout the entire occipital lobe and in the posterior parts of the parietal and temporal lobes. These regions receive fibers from the striate cortex and integrate complex visual input from both hemispheres. From the retina to the visual association cortex, information about form and color, versus motion, depth and spatial information are processed separately.

Non rapid eye movement sleep (NREM)

The state of sleep characterized by slowing of the EEG rhythms, high muscle tone, absence of eye movement and thought like mental activity. It is divided into 4 stages on the basis of EEG, An idling brain in a movable body

Long-term memory (LTM)

The system of memory into which all the information is placed to be kept more or less permanently seems to have a limitless capacity.

Inputs and outputs of cerebellum

Three fiber bundles carry the input and output of the cerebellum. The inferior cerebellar peduncle (also called the restiform body) primarily contains afferent fibers from the medulla, as well as efferents to the vestibular nuclei. The middle cerebellar peduncle (also called the brachium pontis) primarily contains afferents from the pontine nuclei. The superior cerebellar peduncle (also called the brachium conjunctivum) primarily contains efferent fibers from the cerebellar nuclei, as well as some afferents from the spinocerebellar tract.

Uses of EEG

To distinguish different types of epileptic seizures To differentiate "organic" encephalopathy or delirium from primary psychiatric syndromes such as catatonia. To serve as an adjunct test of brain death To prognosticate, in certain instances, in patients with coma To determine whether to wean anti-epileptic medications.

Reticular Formation Nuclei

Traditionally the nuclei are divided into three columns In the median column - the raphe nuclei In the medial column - magnocellular nuclei (because of larger size of the cells) In the lateral column - parvocellular nuclei (because of smaller size of the cells)

Surgical Treatment of Parkinson's disease

Transplantation of adrenal: Transplantation of adrenal medulla from one of the adrenal gland of the patient into his basal ganglia helps in regenerating dopaminergic neurons. Implantation of fetal basal ganglia: Implantation of tissue from fetal basal ganglia into the basal ganglia of the patient. Transplantation of Glomus cells: Recently, isolated glomus cells from carotid body transplanted into basal ganglia has been found to be encouraging. Deep brain stimulation (DBS) is a surgical procedure used to treat several disabling neurological symptoms—most commonly the debilitating motor symptoms of PD, such as tremor, rigidity, stiffness, slowed movement, and walking problems. At present, the procedure is used only for individuals whose symptoms cannot be adequately controlled with medications. Deliver electrical stimulation to specific areas in the brain that control movement, thus blocking the abnormal nerve signals that cause PD symptoms.

Aggression and Rage

Tumors located near the base of the brain but that impinge on the ventromedial hypothalamus have been known to produce marked expressions of violent behavior. The tumors likely have a stimulating effect in causing aberrant expressions of emotional behavior. Such effects may also be due to vascular disturbances and inflammatory disorders.

Damage to the Hippocampus or Amygdala

Typically, for noticeable deficits to occur following lesions to the hippocampus and amygdala, the lesions must be bilateral. Unilateral lesions may not be noticeable or may involve only minimal alterations. Lesions can result in: Changes in memory, including deficits in short-term memory Changes in emotionality, including feelings of fear, anxiety, aggression, and rage Seizures (with a pathologic focus in the anterior temporal lobe, which has a low seizure threshold) Damage rarely occurs through vascular accidents. Trauma and infectious or toxic agents are the primary causes of deficits or dysfunction involving limbic system structures.

Typical Cyclical Pattern of sleep

Typically, there are several cycles of sleep each night. Each cycle begins with a period of REM sleep. Earlier in the night there will be periods of stage 3 and stage 4 sleep, but these diminish towards morning, when there are longer periods of REM sleep and less deep sleep.

Sleep

Unconsciousness from which the person can be aroused by sensory or other stimuli. Reversible behavioral state of unresponsiveness and perceptual dissociation from the environment. Sleep restores strength, mental and physical both. Ability to think and concentrate is enhanced with adequate sleep. Sleep consolidates learning and memory Adequate sleep promotes growth, as GH secretion is high during sleep.

Normal set point of body temperature

Value for core body temperature of about 37°C (98.6°F) is determined by the hypothalamus; There are several effectors for body temperature regulation: ■ Skin circulation is regulated by the adrenergic sympathetic tone; active vasoconstriction minimizes heat loss in response to cold. A reduction in sympathetic tone occurs when the body is hot, which dilates blood vessels in the skin and results in increased heat loss. Further vasodilation occurs as part of the sweating response. ■ Metabolic rate may vary acutely in response to body temperature changes. A low body temperature increases cellular metabolism via activation of the sympathetic nervous system and through increased thyroid hormone secretion. Shivering occurs when the core body temperature falls below approximately 35°C (95°F); it is coordinated by the hypothalamus and occurs first in the proximal muscles. Shivering generates a large amount of heat from muscle but is a short-term response. ■ Sweating is the most important response to increased body temperature due to the large amount of heat needed to evaporate water. Sweat is a hypotonic saline solution secreted by the eccrine sweat glands in the skin in response to cholinergic postganglionic sympathetic innervation. Because the sympathetic nervous system innervates sweat glands (through cholinergic receptors), sweating can be a byproduct of any condition that drives sympathetic output. ■ Behavioral changes that minimize both heat and cold stress occur in response to thermal discomfort; for example, wearing more clothing, eating more, and increasing physical activity in cold weather, or seeking shade, eating less, and reducing activity in hot weather.

Aggression

Violent form of rage. Gonadal hormones (especially testosterone) are known to produce aggressive behaviors. Aggression decreases following castration. Fight or flight response, rage & aggression are fighting behaviors that can be elicited by stimulation of hypothalamic & amygdala nuclei. Removal of connections of frontal cortex to limbic system → more intense & permanent aggressiveness. Bilateral amygdalectomy → permanent placidity.

Cerebral processing of language

Visual and spoken Input into the language areas comes from either the visual cortex (reading) or the auditory cortex (listening). Sensory input from either cortex goes first to Wernicke's area then to Broca's area. After integration and processing, output from Broca's area to the motor cortex initiates a spoken or written action.

Watershed infarcts

When a cerebral artery is occluded, ischemia or infarction occurs in the territory supplied by that vessel, with regions near other vessels relatively spared. In contrast, when the blood supply to two adjacent cerebral arteries is compromised, the regions between the two vessels are most susceptible to ischemia and infarction. These regions between cerebral arteries are called watershed zones (Figure 10.10). Bilateral watershed infarcts in both the ACA-MCA and MCA-PCA watershed zones can occur with severe drops in systemic blood pressure. A sudden occlusion of an internal carotid artery or a drop in blood pressure in a patient with carotid stenosis can cause an ACA-MCA watershed infarct, since the MCA and ACA are both fed by the carotid. Can produce proximal arm and leg weakness ("man in the barrel" syndrome) because the regions of homunculus involved often include the trunk and proximal limbs. In the dominant hemisphere, watershed infarcts can cause transcortical aphasia syndromes. MCA-PCA watershed infarcts can cause disturbances of higher-order visual processing. Watershed infarcts can also occasionally occur between the superficial and deep territories of the MCA

Substantia nigra

center for coordination of impulses essential for skilled movements.

Clinical Presentation of split brain syndrome

patients have been studied by presenting stimuli selectively to one or the other hemisphere and comparing the subject's responses with them. For instance, A stimulus presented briefly to one visual field or placed in one hand is accessible only to the opposite hemisphere (because the projections are contralateral and all commissural connections have been severed). Objects in the right visual field or right hand are recognized and named easily by the 'verbal' left hemisphere. In contrast, patients cannot name, and appear to lack knowledge of, objects placed in the left visual field or left hand, because these are available only to the 'non-verbal' right hemisphere. However, the object has undoubtedly been identified correctly, because the person can later pick it out from a selection of objects. These functional specializations are relative and apply to people with left hemisphere language representation. Subsequent studies have added more detail and complexity. Overall, split-brain work has been central in establishing the extent and nature of functional asymmetries, and its importance was highlighted by Sperry's 1981 Nobel Prize.