Diencephalon & Basal Nuclei

Where does efferent information project to?

- Primary somaotsensory cortex (SI, area 3, 1, 2) of the post central gyrus of the parietal lobe

Where does the dorsal thalamus project to?

- Projects to nearly all areas of the cerebral cortex?

Activation of the direct pathway ____ movement.

- Promotes

How does cholinergic signaling affect firing in the indirect pathway?

- Promotes firing

Which is the largest nucleus in the thalamus?

- Pulvinar

The ____ and the caudate form the ____.

- Putamen - Striatum

What is the dorsal thalamus involved in?

- Receives & passes sensory information and involved in regulating complex cycles

What type of information does the habenular nuclei receive? Which structure receives this info first?

- Receives afferents from the ventral and medial forebrain that arrive though the stria modulars thalami

Most of the fibers in the internal capsule are ___ connections between the thalamus and the ____ cortex.

- Reciprocal - Cerebral

How does the basal ganglia modulate function?

- Release from inhibition (disinhibition)

What shape is the ventral thalamus? Where is it located?

- Resembles biconvex lens - Rostral to the substantia nigra & ventral to the lenticular fasciculus

What do both DA and ACh neuron populations respond to?

- Reward related and novel stimuli, particularly reward-predictive cues

Between which 2 structures does the stria modulars thalami run?

- Runs posteriorly in the groove between the thalamus & caudate

What does the internal medullary lamina do?

- Segments the thalamus into its principle nuclear groups

Regarding the direct pathway, what is the "loop of control"

- Selective movement - Disinhibition of thalamocortical target regions

The principal structure for all ____ and ____ info destined for the ____ cerebral cortex.

- Sensory - Motor - Ipsilateral

What does strong inhibition allow the basal ganglia to do?

- Serve as a master regulatory center - arbitrating between multiple excitatory inputs

When the firing rate of the GPe is inhibited, how does the subthalamic nucleus react?

- Short term excitation

Where is the globus pallidus with respect to the caudate?

- Slightly lateral and ventral

What type of information does the pulvinar process?

- Spatial aspect of visual processing

What efferent fibers are used to get info to the substancia nigra?

- Striatonigrals

Which fibers project efferents to the globus pallidus?

- Striatopallidals

Where are TAN neurons found?

- Striatum

Which structure receives efferents? Via?

- Striatum - Nigrostriatals

From which structures does the globus pallidus receive input?

- Striatum - Subthalamic nucleus - Substancia nigra

To which structures does the SNr send efferent fibers?

- Striatum - Superior colliculus - Parabrachial pontine RF

What do the firing rates in the striatum depend on?

- Strong cortical excitation

Which type of inputs are facilitated thru D1 receptors in the direct pathway?

- Strong, phasic inputs

What is required by those with Parkinson's Disease in order to initiate movement?

- Stronger cortical drive

To which structures does the subthalamus project? (2)

- Substancia nigra - Globus pallidus internus

From which structure does dopamine arise?

- Substancia nigra pars compacta (SNc)

What are the 2 parts of the nigral complex?

- Substancia nigra pars compacta (SNc) - Substancia nigra pars reticulata (SNr)

The majority of the ventral thalamus is the ____ ____.

- Subthalamic nucleus

The majority of the subthalamus is the subthalamic ____, one of the ____ ____.

- Subthalamic nucleus - Basal ganglia

Which structure does the globus pallidus externes primarily project to? By way of?

- Subthalamic nucleus - Subthalamic fasciculus

The ____ is supplied by central (perforating) branches of the ____.

- Subthalamus - Circle of Willis

Which structure sends input to the pulvinar? Which part of the cortex does the pulvinar project to?

- Superior colliculus - Visual association cortex

Does cholinergic signaling suppress or promote movement in the direct pathway?

- Suppress

How does D2 affect the firing rate of the striatum to the indirect pathway?

- Suppress

How is striatal activity affected by D2 receptors in the indirect pathway?

- Suppress

How do D2 receptors affect the firing rates of indirect pathway neurons?

- Suppress firing

Activation of the indirect pathway ____ movement.

- Suppresses

Does cholinergic signaling suppress or promote movement in the indirect pathway?

- Suppresses

Which neurons give off acetylcholine?

- TAN (Tonically active neurons)

The caudate is part of the ____.

- Telencephalon

The putamen is part of the ____.

- Telencephalon

What structure is formed when the ansa lenticularis and the lenticular fasciculus merge?

- Thalamic fasciculus

Disinhibition of which connection will result in movement?

- Thalamocortical

Caudal thalamus, MGB, LGB, and the pulvinar are supplied by the ____ artery, a branch off of the ____ PCA (posterior cerebral artery)

- Thalamogeniculate - P2

Which arteries supply rostral areas of the thalamus? Which part of PCA do they branch from?

- Thalamoperforating arteries - P1 of PCA near the basilar bifurcation

What structures make up the diencephalon?

- Thalamus - Hypothalamus - Epithalamus - Subthalamus

Which structure does the globus pallidus internus primarily project to? By way of? (2)

- Thalamus - Lenticularis & Lenticular fasciculus

What is the physical structure of the thalamus? Which ventricle does it surround?

- Thalamus consists of 2 symmetrical, ovoid masses of tissue - Surrounds the 3rd ventricle

Which structures does the internal capsule separate?

- Thalamus from the globus pallidus and putamen (lentiform nucleus) - Caudate from the putamen

Where do efferents from the globus pallidus project to, eventually making their way to the premotor and supplementary motor areas? Via?

- Thalmus (VA, VL) - Thalamocorticals

What does "ansa lenticularis" mean?

- The handle of the lenticular nucleus

Do the nuclei groups communicate?

- There is NO interconnection fibers among different nuclei groups within the thalamus

What increases with rising task complexity?

- Time delays - Cognitive loading

What type of neuronal firing takes place resulting in the absence of movement?

- Tonic neural firing

What are the 2 types of intrinsic interneurons?

- Tonically active neurons (TAN) - Medium spiny neurons

How does a brief decrease in firing rate affect target regions?

- Transiently release target regions from this inhibition

What is the pineal gland really?

- Underdeveloped third eye

Where does the thalamic fasciculus go to?

- VA thalamus - VL thalamus

What is another name for the subthalamus?

- Ventral thalamus

What 2 divisions is the ventral posterior nucleus separated into? 1 for ____ info and 1 for ____ info.

- Ventro posteromedial (VPM): head related information - Ventral posterolateral (VPL): for body related information

Where is the ventral segmental area located?

- Ventromedial to SNr, unpaired region of the midbrain

Are striatal neurons typically hypo- or hyper-polarized?

- Very hyperpolarized

Are medium spiny neurons active?

- Very little spontaneous activity

Fibers from ____ ____ complex (position sense) and from ____ nucleus (taste)

- Vestibular nuclear complex - Gustatory

What is affected as a result of the anterior choroidal artery syndrome (blockage or stroke)?

- Visual and motor deficits that reflect damage to the optic tract and the inferior portion of the posterior limb of the internal capsule

Which type of inputs are suppressed thru D1 receptors in the direct pathway?

- Weak inputs

What are pinealocytes?

- Weakly light sensitive and receive information concurring light levels though a multi-synaptic neural circuit

What is the extra medullary lamina? Where is it found? What 2 parts of the thalamus does it separate?

- White matter sheath; over covering of the lateral aspect of the dorsal thalamus (medial aspect borders 3rd ventricle) - Blends with projection pathways to separate dorsal & ventral thalamus

Indirect pathways are ____ and ____.

- Widespread - Diffuse

What neurotransmitter do TAN's use?

- Cholinergic

The caudate is involved more so with ____ functions than with ____.

- Cognitive - Movement

What is required to move the striatum into an up state? What is this called?

- Concerted cortical activation to move striatum to up state - Selection mechanism

What type of information is the ventral posterior nucleus a pathway for?

- Conscious awareness of somatic sensation, pain, temperature, touch, proprioception

What does the temporal cortex perceive?

- Conscious awareness of sound

What is the relationship between cortical and striatal activity?

- Constantly oscillating with spontaneous low-frequency membrane oscillations

What does the dorsal thalamus control?

- Control the flow of information from the periphery to the cortex

Where does the habenulointerpeduncular tract send output?

- Conveys output to descend to paramedian midbrain reticular nuclei

Which structure fans out above the internal capsule?

- Corona radiata

Almost all nuclei send fibers to the ____ and receive ____.

- Cortex - Reciprocal connections

Regarding the motor loop, what structures make up the motor loop?

- Cortical input (Primary motor cortex, Premotor, Supplementary cortex) - Striatum (Putamen) - Pallidum (Lateral globus pallidus, internal segment) - Thalamus (Ventral lateral and ventral anterior nuclei)

What are the 2 tracts going thru the internal capsule?

- Corticothalamics - Thalamocorticals

Which layers are crossed?

- Crossed fibers to layers 1, 4, 6; Nasal hemiretinas

Which population of dopamine receptors are associated with the direct pathway?

- D1

Which population of dopamine receptors are associated with the indirect pathway?

- D2

Where do efferent fibers project to preferentially? What other areas?

- D2 neurons of the striatum - Ventral striatum, limbic, and neocortical areas

What affect does the D2 have on Ca++ currents? Less positive charge ____ the neuron.

- Decreasing Ca++ currents - Enters

Which other structures observe patch boundaries?

- Dendritic arbors

Where do medium spiny neurons receive input from to be active? With which disease are the lost?

- Depend on excitatory input for discharge (from corticostriates mainly) - Huntington's disease

Effect of indirect pathway output on GPi/SNr?

- Diffuse, widespread excitatory contact

What promotes movement? Which circuit discharge?

- Disinhibited thalamocortical circuit discharges promoting movement

Movement modulation (section) occurs through ____.

- Disinhibition

What has to happen in order for movement to take place?

- Disinhibition of thalamocoritcal target regions

What results from damage to or disorders of the basal nuclei?

- Disruption of movements

VAT is ____.

- Dopamenergic

SNc are ____ neuromodulators. These are lost with ____ disease.

- Dopaminergic - Parkinsonism

What is the largest division of the thalamus?

- Dorsal thalamus

Which layer is more dorsal? Ventral?

- Dorsal: Substancia nigra pars compacta (SNc) - Ventral: Substancia nigra pars reticulata (SNr)

How many nuclei make up each half of the thalamus?

- Each half can be divided into numerous nuclei (~26)

In the direct pathway, narrowly focused GPi/SNr inhibition leads to thalamic ____.

- Excitation

What affect does inhibition of GPi/SNr firing have on the thalamus?

- Excitation of thalamus

Is the subthalamic nucleus inhibitory or excitatory?

- Excitatory

Does D2 activity on the indirect pathway facilitate or inhibit movement?

- Facilitate

How are strong cortical inputs affected by D1 activity in the striatum?

- Facilitated

How does D1 presence/activity affect the direct pathway?

- Facilitates movement

What is the ultimate net effect? For?

- Facilitation of movement in response to reward predictive cues, selection action to get reward

What is another name for the habenulointerpeduncular tract?

- Fasciculus retroflexus

What is the habenula functionally implicated with? Via?

- Fear & "reward negative" responses via caudally directed limbic projections

From where does the LGB receive afferent information?

- Fibers from retina/optic nerve (crossed fibers to layers 1, 4, 6)

Effect of direct pathway output on GPi/SNr?

- Focal inhibitory contact

Direct pathway inputs are ____ and ____.

- Focused - Dense

The diencephalon is the caudal most subdivision of the embryonic _____?

- Forebrain (prosencephalon)

The substancia nigra pars reticular is ____ but interconnected with ____.

- GABAergic - SNc

Where does the SNc receive afferents from?

- GPe - Parabrachial pontine RF

Which structure is this similar to?

- GPi

The SNr is a major output of basal ganglia (with ____) for the ____ selection loop.

- GPi - Motor

What do the basal ganglia do?

- Generation and selection of goal-oriented voluntary movements

Which structures does the anterior choroidal artery go into?

- Genu - Posterior limb of internal capsule

What dose the pineal gland help with?

- Give the brain information to adjust circadian rhythm functions: sleep, body temp, appetite, etc.

To which structures does the striatum project efferent fibers?

- Globus pallidus - Substancia nigra

Which part of the globus pallidus is part of the indirect pathway? Direct pathway?

- Globus pallidus externus (lateral, GPe) - Globus pallidus internus (medial, GPi)

Unlike any of the basal ganglia, the subthalamus is ____?

- Glutamatergic (excitatory); most of the basal ganglia are inhibitory

What is a result of a vascular lesion on the subthalamus?

- Hemiballismus

Does the SNr have a high or low rate of discharge?

- High

Firing rates given off by the GPe neurons are very ____.

- High

What is maintained by the basal ganglia in order to maintain suppressed (inhibited) thalamic activity?

- High tonic level of discharge

What do the output nuclei of the basal ganglia maintain? What affect does this have on target regions?

- High tonic level of discharge - Suppress activity in tonic regions

What specifically?

- Homonymous - Hemianopsia - Contralateral hemiparesis - Hemianesthesia

Which arteries does the anterior choroidal artery come from?

- ICA (internal carotid artery)

Where does the diencephalon begin?

- Imaginary line between the posterior commissar & mammillary bodies

What does the subthalamic nucleus keep in check?

- Inappropriate motor commands

DA neurons ____ their firing. ACh neurons ____ their firing.

- Increase - Decrease

How does the disinhibited firing rate of the subthalamic nucleus affect the firing rate of the output nuclei (GPi/SNr)?

- Increase suppression of connected thalamus

With D1, what occurs in the up state? More positive charge ____ the neuron.

- Increases voltage-dependent Ca++ current - Enters

With D1, what occurs in the down state? More positive charge ____ this neuron.

- Increases voltage-dependent K+ current - Leaves

What is necessary for rising task complexity?

- Increasingly sophisticated neural loops for action selection

Which pathway does the subthalamus participate?

- Indirect pathway for action selection

Where does the ansa lenticularis emerge from?

- Inferior surface of the globus pallidus

How does cholinergic signaling affect firing in the direct pathway?

- Inhibit firing

Ultimately, what does the net effect of ACh want to do?

- Inhibit movement

High firing rates of the GPe keeps the subthalamic nucleus tonically ____.

- Inhibited

Indirect pathways lead to widespread GPi/SNr excitation which will become thalamic ____.

- Inhibition

What affect does the striatum have on GPi/SNr firing?

- Inhibition of GPi/SNr firing

Are output nuclei of the basal ganglia inhibitory or excitatory?

- Inhibitory

Output nuclei of the basal ganglia are ____ to the thalamus via ____ fibers.

- Inhibitory - Thalamocortical

The putamen and caudate (together) are thought to be the ____ layer of the basal ganglia.

- Input layer

Diencephalon literally means...?

- Interbrain

What are the 2 parts of the globus pallidus?

- Internal - External

What is the lateral boundary of the diencephalon?

- Internal capsule

Efferent fibers travel thru the ____ and project primarily to the ____ (area 4)

- Internal capsule - Primary motor area

Which structures are rostrally bound to the diencephalon?

- Interventricular foramen of Monroe - Lamina terminalis - Optic chiasm

What type of neurons are found in the striatum?

- Intrinsic interneurons

How do the thalamocortical pathways respond to the GPi/SNr excitation?

- Inverse result across thalamocortial pathways

What is the internal medullary lamina made of?

- Investment of the white matter

What is hemiballismus

- Involuntary disorder on the contralateral side - Produce rapid, forceful flailing

MGB projects efferent information to the ____ & temporal cortex.

- Ipsilateral insular

Where do the efferents project to? By way of?

- Ipsilateral side of the occipital cortex - Optic radiations (geniculocalcarine)

What other structures does the anterior choroidal artery supply?

- Optic tract - Inferior part of the lenticular nucleus - Choroid plexus of the lateral ventricle - Much of the amygdala - Retrolenticular limb of the internal capsule - Large parts of the hippocampal formation

Where do ~10% of the synapses in the thalamus come from?

- Outside afferents

Caudal hypothalamus, the ventral thalamus, and subthalamus are served by branches off ____ PCA.

- P1

What is another name for the globus pallidus?

- Paleostriatum

Which structures make up the epithalamus?

- Pineal gland - Habenulus - Stria medullaris

What is the ventral anterior nucleus involved with?

- Planning - Initiating movements

What is the ventral segmental area known as?

- Pleasure center of the brain

What do the posterior and medial posterior choroidal arteries supply? Which segment of the PCA do they branch from?

- Portion of the caudal and medial thalamus - P2

Where is the epithalamus located?

- Posteriocaudally, close to the posterior commissure

Which structure does the ansa lenticularis "hook around" in order to get to the thalamus?

- Posterior limb of the internal capsule

What causes a striatal neuron to transition from down state to up date? (_ mV)

- Potentials correlated among nearby striatal neurons - -50mV

What type of information do tonically active neurons carry?

- Predictive information about reward value of any target

What areas of the cortex is the caudate connected to?

- Prefrontal & other association areas

Where do the efferent fibers project to? (Name and area)

- Premotor cortex/ supplementary motor area (Area 6) of the frontal lobe

Medium spiny neurons are ____ ____ neurons. They are GABAergic and ____ neurons.

- Primary projection - Inhibitory

How are the direct and indirect pathways of the basal ganglia different?

Direct pathway - Facilitates the flow of information through the thalamus - Promotes movement Indirect pathway - Inhibits the flow of information through the thalamus - Inhibiting movement

Direct Pathway

Facilitates movement

Indirect Pathway

Suppresses movement

The basic circuit is divided into 2 pathways with ____ actions.

- Opposing

The diencephalon is the main processing center for information designed to reach what structure?

- Cerebral cortex

From w which 2 structures does the neostriatum receive afferent information?

- Cerebral cortex - Substancia nigra pars compacta

Where do the corona radiate fibers go below the internal capsule?

- Cerebral peduncle

Substancia nigra pars compacta by way of ____.

- Nigrostriatals

What is one exception?

- Olfactory information passes through the thalamus only indirectly

How are D1 and D2 receptor populations arranged? These areas are ____ separate areas.

- On different neuron clusters - Neurochemically separate

What is found in the ventral segmental area?

- Opioid receptors (pleasure center of the brain)

Which 2 structures form the striatum?

- Caudate - Putamen

From which 2 structures does the VL nucleus receive afferent input?

- Cerebellum (mainly from the dentate nucleus) - Basal ganglia (small input)

What does the pineal gland consist of?

- CT - Glia - Pinealocytes (endocrine function, not true neurons)

The (dorsal) thalamus is called the ____ to the cerebral cortex.

- "Gateway"

What is the down state of a striatal neuron?

- -80 mV

How long is the pineal gland? Where is it located?

- 1 cm long - Found caudal to the posterior margin of the corpus callosum and the cerebellum

How many parts or divisions make up the globus pallidus?

- 2, reciprocally connected

The diencephalon is symmetrically arranged around (and separated medially by) ___?

- 3rd ventricle

How many layers make up the lateral geniculate nucleus?

- 6

What % of the neurons in the striatum are these?

- 90%

What are habenular nuclei? Where are they found?

- A small mound of neurons on the dorsomedial surface of the posterior thalamus

From which segment of the ACA does it branch 10% of the time? 90%

- A1, 10% - A2, 90%

Where is each later of the internal capsule located and to what areas of the brain are they associated with?

- AL: links thalamus to frontal lobe - Genu: sends fibers from cortex to cranial nerve nuclei (corticobulbar) - PL: connection with parietal lobe - RL: behind lenticular nucleus; connection btw lateral geniculate body (LGB) and occipital lobe - SL: connection between MGB and temporal lobe

Which systems does the hypothalamus control?

- ANS/endocrine system

In those with Parkinson's, what happens with the indirect pathway?

- Action inhibition is effectively facilitated

Together the direct and indirect pathway create a center-surround mechanism for ____ ____.

- Action selection

In those with Parkinson's, what happens with the direct pathway?

- Action selection is effectively suppressed

Co-activation of direct and indirect pathways?

- Action selection through a center-surround mechanism - Winner take all choice of action

____ and ____ are distinct. How are loops organized to reflect this?

- Afferents - Efferents - Keeps processing loops separate

From which tracts does the ventral posterior nucleus receive afferents?

- All fibers of the medial lemniscus - Most of the spinothalmic - Most of the trigeminothalamic

Direct pathway activation ____ movement via thalamic ____ of ____ targets.

- Allows - Excitation - Cortical

Just prior to which structure does the tail of the caudate end?

- Amygdala

What are the 3 organizational principles within the basal ganglia for connectivity?

- Anatomicall parallel loops with distinct functions - Fine-grain topographic organization within distinct loops - Patch/matrix architecture

In what 2 ways are the basal ganglia segregated? Why?

- Anatomically & functionally segregated into parallel circuits that process different types of information

What are the 5 areas of the internal capsule?

- Anterior limb - Genu - Posterior limb - Retrolenticular portion - Sublenticular portion

What are the principal nuclear groups and what is associated with each?

- Anterior: related to limbic function & circuit of Papez (emotion) - Medial: may be related wit memory and the perception of pain - Lateral: dorsal & ventral tiers, sensory transmission - Intralaminar - receive afferent fibers from reticular formation, involved with consciousness & arousal

What results in motor learning? (Neurochemical alteration)

- Balance of inhibition and excitation

From which structures does the ventral anterior nucleus receive most of its afferent input?

- Basal ganglia, especially the globes pallidus internus (GPi) and substancia nigra, pars reticulata (SNr)

The MGB receives ____ auditory input.

- Bilateral

What does "substancia nigra" mean?

- Black substance

What are other names for the pineal gland?

- Body - Epiphysis cerebri

From where does the medial geniculate body receive afferent information?

- Brachium of the inferior colliculus - Fibers from internal capsule - Bilateral auditory input (majority contralateral)

TAN's have ____ cell bodies and are very active (> ____ Hz).

- Large - 100 Hz

Selection through surround inhibition occurs on ____ and ____ scales.

- Large - Small (i.e. not only reach left or right, but how far to reach)

Which nuclei makes up the lateral group, dorsal tier?

- Lateral dorsal - Lateral posterior - Pulvinar

What is formed by the joining of the globus pallidus and putamen?

- Lenticular/lentiform nucleus

Which arteries (off of M2 of MCA) supply the internal capsule, globus pallidus, and putamen?

- Lenticulostriate

What arteries serve most of the basal ganglia?

- Lenticulostriate arteries (most from M1 segment)

Direct pathway becomes ____ active, while indirect pathway becomes ____ active.

- Less - More

How does normal firing from the striatum affect Gpi/SNr discharge?

- Little impact

90% of the synapses in the thalamus originate from ___ and deciding outputs from ___.

- Local inhibitory neurons - Cerebral cortex

Tonic firing rates in the striatum are normally very ____.

- Low

Striatal neurons have ____ tonic firing rates; depending upon strong ____ inputs

- Low - Cortical

Off which segment of the MCA do the lenticulstriate arteries come off?

- M1

What is the function of the diencephalon?

- Main processing center for information destined to reach the cerebral cortex (relay structure)

What is made by pinealocytes?

- Makes and releases melanin, more strongly in the absence of light

With respect to the putamen, the globus pallidus is located immediately ____.

- Medial

What are other names for the recurrent artery of Heubner?

- Medial striate a. - Long central a.

Where does the lenticular fasciculus emerge from? What does it cross?

- Medially - Internal capsule

Aside from TAN's, what other type of intrinsic interneuron is located in the striatum?

- Medium spiny neurons

Where is the nigral complex found?

- Midbrain, just dorsal to the crus cerebri

Witch regard to the indirect pathway, what results with brief excitation of the striatum? (How is the firing rate from the GPe affected?)

- Momentary transient inhibition of GPe firing

The ventral lateral nucleus is involved in ____ feedback from the ____ and the ____ to the cerebral cortex

- Motor - Cerebellum - Basal ganglia

Cerebral cortex (primarily ____ and ____ areas) by way of ____.

- Motor - Somatosensory areas - Corticostriatals

From which structures does the subthalamus receive input? (3)

- Motor cortex - Globus pallius - Substancia nigra

What structures are involved in the indirect pathway?

- Motor cortex - Striatum - GPe - STN (subthalamic nucleus) - SPi/SNr - Thalamus

What structures are involved in the direct pathway?

- Motor cortex - Striatum - GPi/SNr - Thalamus

What functions is the putamen prominently involved with?

- Motor function of the basal ganglia

"Structured disinhibition" allows for ____.

- Motor pattern selection

Activation of the indirect pathway prevents ____ via increased thalamic ____.

- Movement - Inhibition

What are other names for the striatum?

- Neostriatum - Dorsal striatum - Caudate + Putamen

Diseases of the basal ganglia can be described as disruptions of ____ ____.

- Neurochemical interactions

What do the neurons of the substancia nigra contain?

- Neuromelanin