Cerebral Cortex Functions and Lesions

Conduction Aphasia

*Fluent Aphasia* Lesion in *auditory cortex*, the patient has no trouble speaking or hearing but has trouble *putting words together or conjuring up words* -NOT wernike's!

Wernicke's Aphasia

*Fluent aphasia* -Resulting from lesion in Wernicke's area in *posterior part of superior temporal lobe*, involves difficulty in comprehending speech and in reading. -WORD SALAD -CANNOT repeat --- Fluent, often rapid, voluble, and effortless (nonstop words) -Inflection and articulation are good, but sentences LACK meaning -Words are malformed or invented -Speech may be totally incomprehensible (no real words) -Word comprehension, repetition, naming, reading comprehension, and writing are impaired -AUDITORY AREA: Lesion hear will cause problems hearing and comprehension >Wernike's Aphasia is near auditory -Test: Point at tie or shoes-> will comprehend visual cues >NOT comprehend auditory

Handedness

*Handedness*: Approximately 90% of human population is RIGHT handed. -The *categorical hemisphere* in 96% of right-handed individuals is the LEFT hemisphere. >Only 4% of right-handed individuals have the RIGHT hemisphere specialized for categorical analysis. -10 % of the population is LEFT handed >70% of left-handed individuals have the left hemisphere as the categorical hemisphere. >15% of left-handed individuals use the right hemisphere as the categorical hemisphere. >15% of left handed individuals unclear as to which hemisphere is categorical

Agnosia

*Lesions of left or right parietal-temporal lobes produce* "Not knowing", inability to recognize a complex sensory stimulus such as an object even though sensory pathways and perception of the object are intact. -Patients cannot identify or name the object even though sensory pathways are functioning normally. -Astereognosis -Prosopagnosia -Anosognosia: Unaware of disability

Gerstmann's Syndrome

*Parietal Lobe Lesion* -Confusion between right and left sides. -Difficulty in saying which finger was touched. -*Dysgraphia*: Writing disability. -*Dyscalculia*: Inability to do mathematical calculations

Functions of the Association Cortices

*Prefrontal cortex*: Cognitive behavior and motor planning and maintenance of an individual's personality. -Weigh consequences of actions being considered. ("Should I do...") -Carry out motor tasks involving memory or in relation to sensory inputs. >Lesions are often interpreted as a change in the patient's character >Lesions in the frontal lobe are diverse and devastating, especially if BILATERAL ->Patients become boastful of physical prowess and LITTLE restraint in conversation, unable to plan for the future. ->ACA can infarct PFC -*Orbito-ventromedial PFC*: Lesions produce cognitive EMOTIONAL abnormalities. >Problems with being aware happy/unhappy -*Dorsolateral PFC*: Lesions produce abnormal cognitive executive control and goal setting behaviors (Can't decide on menu, plan goals, etc)

Association Cortex

*Remaining 75% of human neocortical tissue* -*"Silent Areas"*: Substrate of HIGHEST brain function-> cognition-> "knowing" -Main association areas and integrative abilities of association cortex. >*Prefrontal*: Location of delay-> specific neurons and mirror neurons. ->Ex: See student putting fingers on keys-> motor neurons association my hand movement as if tapping the keys will also fire (even though not tapping anything)-> helps me understand what is happening/recognize behaviors (I know you are tapping)-> Learn behavior by watching and having mirror neurons fire >Planning behavior, setting goals, recognizing behaviors. >Continues to fire but delays gratification-> fires during delay before you get what you want >Bought tickets to go home in December-> keeps firing and tell you do NOT forget going home >*Parietal*: Location of *attention-specific neurons*-> attending to COMPLEX stimuli. >WHERE pathway >*Temporal*: Location of recognition-specific neurons-> *Recognizing and identifying objects* >WHAT pathway

Contralateral Neglect Syndrome

*Tendency to neglect the opposite (usually LEFT) side of body* -*Left hemisphere* attends only to the RIGHT half of the body and extrapersonal space, thus a lesion of the *left parietal lobe* (Problems with ATTENTION) will be compensated by the right hemisphere. -Problem occurs when the right hemisphere is damaged, there is no compensation by the left hemisphere for the left side of the body, and thus it is neglected (*hemiasomatognosia*). ---- Neglect left side: Only shave right side of face, eat right side of plate, turn right only when walking

Lesions NOT well localized (PTO)

-Apraxia -Contralateral Neglect Syndrome

Anomic Aphasia

-Damage to the *angular gyrus* -Unable to NAME objects

Broca's Area

-In PFC: Pars Triangularis -Blood supply from MCA Superior Division -Ability to EXPRESS what you are think orally and in writing -Expressive Aphasia: Can think of the thought, but cannot express it in words (NON-fluent expressive or motor aphasia)->Cannot express thoughts >Ex: Can only say two words (So what which is very difficult-> can't say anything else) --- Cortex affected-> gray matter lesion (NOT dysarthria)

Contralateral Neglect Syndrome (Picture)

-Left parietal: Only attention for RIGHT half -Right parietal: Attention for RIGHT and LEFT -Lesion of RIGHT parietal lobe: CONTRAlateral neglect syndrome (neglect the left) -Ex: Neglect left side of clock!

Left Hemisphere (Lesion)

-Lesions in the categorical hemisphere (usually left cortex) cause *language disorders* (Aphasia) >Left MCA can be involved >Extensive lesions in the representational hemisphere (Right) do not. -Patients are usually AWARE about their disability and often DEPRESSED --- Ex.) Patient having trouble analyzing, verbalizing, and cataloging-> problem with left hemisphere (generally is the area that is involved in categorical info-> especially in right handed patients) >REMEMBER: Right or left handed-> most people use left hemisphere for categorical info

Association Cortex (Function)

-These regions are responsible for the information processing that goes on between sensory input and motor output. -The diverse functions of the association cortices can be thought of as *cognition*, which describes our ability to know our world by the ability to attend, identify, and plan responses to internal motivation and external demands. -Based on mapping studies: >The *frontal association* cortices are essential for PLANNING appropriate behavioral responses, >The *parietal association* cortex is responsible for ATTENDING to complex stimuli in the external and internal environment, >The *temporal cortex* is required to IDENTIFY the stimuli.

Left Hemisphere

CATEGORICAL (Sequential/analytical) -Left hemisphere specializes in intellectual, rational, verbal, analytical thinking, and in *declarative* memory. >Talks to you! >DECLARE -This hemisphere is concerned with categorization and symbolization once called the DOMINANT hemisphere-> Now called the *categorical hemisphere*

Frontal Lobe Syndromes (table)

CONTRADICTORY behavior -Apathetic: Showing no interest -Abulia: Absence of willpower (can't pick from menu) -Akinesia: Lose power of movement (Frozen) -Mutism: Not speaking -Confabulation: Fabricate imaginary experiences

Asymmetry of cerebral cortical function

Concept of DOMINANCE of one hemisphere over the other is replaced with the idea of *complementary specialization* of the hemispheres. -One hemisphere is specialized for sequential and analytical processes. >*CATEGORICAL* hemisphere= Left (Dominant) -> No emotion ->Left= Language -The other one for the visuospatial relations >REPRESENTATIONAL hemisphere= Right (NON-Dominant) -> How many? Feel good?

Psychosurgery (Picture)

Connection of ipsilateral frontal cortex to PTO *Arcuate fasciculus* cut bilaterally with stylus (isolate PFC from PTO) By cutting arcuate fasiculus-> Disconnect PFC-> Where strategy, emotion, and ability to act on those emotions-> All of these things are STOPPED-> Patient becomes DOCILE,etc >Don't care where urinate, can't switch strategies, etc -Procedure no longer done!

Aphasia (general)

Disorder in producing or understanding language -Reciprocal connections between Broca's and Wernicke's-> Can have lesion of these fibers instead of Broca's or Wernicke's itself-> Other aphasias Cortical lesion --- Aphasia NOT happen in capsular stroke (white matter), instead dysarthria occurs

Different MCA Lesions (Table)

Entire left MCA= GLOBAL Aphasia Superior branch of left MCA= Broca's Aphasia Inferior branch of left MCA= Wernicke's Aphasia

Parietal-temporal association cortex

Higher sensory functions and language. -Lesions of *categorical* (usually LEFT-> language) parietal- temporal lobe produce: -Aphasia= Disorder of language >Wernicke's Aphasia >Conduction Aphasia >Anomic Aphasia >Global Aphasia

Apraxia

INABILITY to perform an action in response to a *verbal command* ("unlock the door") in the absence of any defect in comprehension, incoordination, or motor weakness. -Lesions of the NONdominant, representational (usually RIGHT) parietal lobe produce: >No obvious disturbances of language but inability to appreciate emotional aspects of a verbal message conveyed by tone, loudness, and timing or express emotion in speech (aprosody)-> *INFERIOR parietal lobe* --- Lesion on right: Is patient Euphoric-> Yes and do not know or care-> Anosognosia No language problems with right sided lesions! (no emotions when right sided)

Astereognosis

INABILITY to recognize the form of objects by touch alone, with no major somatic sensory deficits. Picture: Closed eyes and has pen in hands (cannot describe holding alone)

Global Aphasia

LOSS of all language skills: comprehension, speaking, reading, and writing -MCA (left) damage -Visual field cut as well >Contralateral hemonimous heminopia ->Optic radiations affected (White matter lesion)

Extent of human association cortex

Lateral and medial views of the human brain show the *association cortices* in BLUE -he primary sensory and motor regions of the *neocortex* are shown in yellow. -Notice that the primary cortices occupy a relatively sMALL fraction of the total area of the cortical mantle. -The remainder of the neocortex-> defined by exclusion as the association cortices-> is the seat of human cognitive ability. -The term association refers to the fact that these regions of the cortex integrate (associate) information derived from other brain regions. --- CF= calcarine fissure -Vision is in the medial surface Olfactory in medial Cortico-cortical tract (Layer 2/3 connections between hemispheres) -> Corpus callosum, arcuate fasciculus, etc

Broca's Aphasia

Lesion in Broca's area in the *INFERIOR part of the PFC* results in Broca's aphasia= difficulty in expressing thoughts either in written (agraphia) or in spoken language (nonfluent, expressive, or motor aphasia) Non-fluent and slow, with few words, and laborious effort -Inflection and articulation are impaired, but words are real and meaningful -Small grammatical words are often dropped -Repetition, naming, and writing are impaired -Word and reading comprehension are fair to good -- NO auditory problems -Cannot repeat

Right Hemisphere (Lesion)

Lesions of the representational hemisphere produce *agnosias*: General term used to describe the *inability to recognize* objects by a particular sensory modality even though the sensory modality itself is intact >Agnosia is a CORTEX problem (not tract!) -These lesions are usually in the *temporal and parietal lobes* -A lesion in the *inferior parietal lobe* is the primary region responsible for ATTENTION ("Attending") -Patients may be unaware of their disability (*anosognosia*-> deficit of self-awareness) and are UNCONCERNED even euphoric >Unable to recognize emotions in other individuals! -- Usually damage in right cortex-> NO APHASIA Everything is working in categorical sense but association cortex CANNOT put together so they cannot recognize what the object is! -Oblivious to fact they have a lesion! -Cannot recognize emotions in others or give emotion to their own tone-> APROSODY= NO EMOTION IN LANGUAGE -Someone usually takes/refers them to hospital

PFC and Limbic System

Limbic System important part of pre-frontal lobe: *emotional behavior and memory* -Individuals with lesions of the orbitofrontal cortex have LESS profound emotional responses, REDUCED anxiety, lack of inhibition of inappropriate behaviors, lack of initiative, difficulty in changing strategies, yet no change in global intelligence as measured on standard tests. >Psychosurgery

Right Hemisphere

REPRESENTATION (Visuospatial relations) -Right hemisphere (non dominant) specializes in perceiving and in emotional, nonverbal, and intuitive thinking, and in *procedural* (non-declarative) memory. -It appears *sustained attention* to a polymodal task in humans is a function of the representational hemisphere. -It is involved with recognition of objects by their form and the recognition of musical themes

Brodmann's Area

Regions of the Cerebral Cortex -Association cortex

Prosopagnosia

Unilateral or bilateral *temporal lobe damage* results in the INABILITY to recognize old faces or remember new faces, with NO vision pathway deficits