Hemispheric Organization

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NEUROPHYSIOLOGY: HEMISPHERIC ORGANIZATION Page 1

CEREBRAL CORTEX

In the figure above the white portion is the cerebral cortexwhich contains 6 layers and is also known as neocortexwhich is sometimes known as the seat of intelligence. Thelimbic system (the blue portion) is a 3 layered cortex and itsfunction has something to do with instinctual behavior.

There are also transition areas between the white and blueportion which consists of 5-6 layers. Comparing with othermammalian cortex, humans have thicker neocortex.Though animals like dolphin and elephants which havecertain amount of intelligence akin to those of humans.

There are 3 species that have bigger brain waves thanhumans. Examples are sperm whales, dolphins andelephants. Though humans have a bigger brain waves tobody ratio. The frontal and prefrontal cortex plays as acentral executive function in animals not only humans.

Another important feature of the neocortex especially of the

humans is the increase in foldings which allows for highlypacked neuronal circuit just like computer chips. Foldingsalso increases surface area underneath are circuits whichmight be the secret of intelligence in humans.

Cortical associations areas are areas in the brain adjacentto the motor and sensory cortex which is important formotor and sensory signal processing . It also plans outpatterns for movements and other actions in the body. Thecortical association areas also have something to do withhigher order processing of somatosensory information.Example there is an expanded frontal association area herecompared to other mammalian species. The limbic

association and the parietooccipital association areas arealso expanded areas.

I. THE CEREBRAL CORTEXA. Overview of the cerebral cortex: Basic Neural

Circuitry of the 6-layered NeocortexCortical Layers Characteristics/ Function

(note: there are manyinterneurons in differentlayers)

Layers I III (Molecular,External Granular, ExternalPyramidal)

Layer I also containsHorizontal cells of Cajal;Pyramidal cells in variouslayers

Numerous stellate cells,which indicate that thesethree layers are important

for association and higherfunctions such as memory,interpretation of sensoryinput and certaindiscriminative functions..Receives association andcommissural fiber inputs;Pyramidal cells from theselayers also send efferents toother cortical areas asassociation andcommissural fibers. Layers I IV also receive non-

specific afferents (reticularafferents and afferentinputs frommidline/intralaminarthalamic nuclei).

Layer IV (Internal GranularLayer)

Mainly a RECEPTIVE LAYER(thalamocortical ascending fibers end here).Mainlyspecific afferents fromsensory pathways

Layer V and VI (InternalPyramidal andMultiforum/Fusiform Layer)

Primarily efferent layers thatcontain nerve cell bodieswhose axons enter thecorticospinal tract(descending fibers)..Martinotti cells inLayer VI sends afferents tosuperficial layers. MainProjection neurons tosubcortical structures arepyramidal, plus fusiformcells. In motor cortex, Betzcells are the large pyramidalcells located here here.

SUBJECT: NEUROPHYSIOLOGY

TOPIC: HEMISPHERIC ORGANIZATION

LECTURER: DR. SIMBULAN

DATE: MARCH 2011


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B. How the various cortical regions areinterconnected with each other, and withsubcortical regions: Through Association,Commisural and Projections Fibers

y Association Fibers are nerve fibers that interconnectcortical regions of the same cerebral hemisphere

y Commisural Fibers cross the midline andinterconnect similar cortical regions in the two cerebralhemispheres

y Projection Fibers connect cortical areas of thecerebrum with subcortical regions.

Below are major association and commisural fibers of thecerebrum:

y ASSOCIATION FIBERS on the LATERAL aspect of the cerebral hemisphere

o UNCINATE FASCICULUS (uncinate meanshook-shaped) interconnects the cortexof the uncus (of hippocampal gyrus) andtemporal pole with the inferior frontalregion

o INFERIOR OCCIPITOFRONTAL FASCICULUS is locaed along the inferior portion of theextreme capsule, dorsal to the uncinatefasciculus. It interconnects the cortex of the lateral or inferolateral portion of thefrontal lobe and cortex of the occipital lobe,with connections along the way, including

the inferior temporal and fusiform gyri of the temporal lobe

o Superior Longitudinal Fasciculus islocated along the dorsolateral border of the putamen, lateral to the internalcapsule. It underlies and interconnects thecortices of the frontal, parietal, andoccipital lobes and arches inferiorly and

anteriorly with connections in the temporallobe cortex.

o Arcuate Fasciculus - curves over andaround the posterior part of the insula topass into the temporal lobe. It is acontinuation of the superior longitudinalfasciculus (synonym for superiorlongitudinal fasciculus).

o Lateral Occipital Fasciculus (also knownas vertical or perpendicular occipitalfasciculus and as the fasciculus of Wernicke) - passes vertically through theoccipital lobe and interconnects thefusiformgyrus of the temporal lobe and theposterior part of the parietal lobe.

o Inferior Longitudinal Fasciculus -interconnects occipital lobe cortex andtemporal lobe cortex in the inferior andlateral portion of the hemisphere.

y ASSOCIATION FIBERS on the medial aspect of thecerebral hemisphere

o Stratum Calcarium refers to a well-developed sheet of fibers curving around

the bottom of the calcarine fissure fromthe cuneus above to the lingual gyrus.o Cingulum (means girdle) is an

association bundle of the cerebrumlocated within the cingulategyrus. It hasconnections all along its course withadjacent frontal, parietal and temporallobe cortex. Superior Occipital Fasciculus - is

located along the caudate nucleusmedial to the interdigitating fibers of the internal capsule and corpuscallosum. Its fibers interconnect thecortex of the occipital and temporallobes with those of the frontal lobeand insula(synonym for subcallosalfasciculus).

y ASSOCIATION and COMMISURAL FIBERS in coronalsection of cerebral hemisphere

o Corpus Callosum (Means hard body) isthe thick band of commisural fibersinterconnecting areas of the neopallium(cerebral cortex and underlying whitematter)

o Cingulumo Superior and Inferior Occipitofrontal

Fasciculio Superior Longitudinal Fasciculuso Arcuate Fasciculuso Uncinate Fasciculuso Anterior Commisure


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C. Overview of localization of Cerebral functions(Sensory, Motor< and Integrative, HigherFunctions) Below is a partial listing of effectsof lesions:

STRUCTURE FUNCTION EFFECTS of LESION/ABLATION

Frontal Lobe Resonating,Motivation,modulation of emotions, partsof speech andmovement(motor cortex) ,and problemsolving.....

Effects of lesions inorbitofrontal cortex or Prefrontal lobotomy inability tosolve complexproblems; unableto string together sequential tasksto reach aspecific goal;decreasedaggressiveness;loss of ambitionand motivation;lack of socialinhibition;comprehendlanguage butunable to carrythrough aconversation;mood swings;purposelessactivities; lack of general concern.

Lesions in theventromedialportions of Frontal Lobe

is calledConfabulation.Individuals withthis conditionperform poorlyon memory tests,but theyspontaneouslydescribe eventsthat never occurred (honestlying).

Parietal Lobe C oncerned with

perception of stimuli related totouch, pressure,temperature andpain

See also other

effects in tablesbelow and abovethis (Especiallywith regards tovisuo-spatialprocessing; notethat there is ad orsal (parietal)pathway from theoccipital lobe invisual signalprocessingextending intothe parietal lobe)

Occipital Lobe C oncerned withmany aspects of vision

Fibers from thelateral geniculatebody thatsubserve macularvision separatefrom those thatsubserveperipheral vision

and end moreposteriorly on thelips of thecalcarine fissure.Because of thisanatomicarrangement,occipital lobelesions mayproduce discretequadrantic visualfield defects(upper and lowerquadrants of eachhalf visual field).

Macularsparing,ie, loss of peripheral visionwith intactmacular vision, isalso common withoccipital lesions,

because themacularrepresentation isseparate fromthat of theperipheral fieldsand very largerelative to that of the peripheralfields.

Occipital lesionsmust extend

considerabledistances todestroy macularas well asperipheral vision.Bilateraldestruction of theoccipital cortex inhumans causessubjective

blindness . Temporal Lobe C oncerned with

perception and

recognition of auditory stimuli(hearing),memory(hippocampus),as well asemotions(amygdala andperiamygdaloidstructures)

See also other effects in tables

below and abovethis. Note toothat there is av entral (temporal)pathway from theoccipital lobe invisual signalprocessingextending intothe temporallobe.

(Learning and

memory functions,which involve thehippocampus,and variouscortical areas, aswell as the basalganglia andcerebellum, areconsidered in


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detail in aseparate handoutand lecture.)

Corpus Callosum C onnectingbridge betweentwo hemispheres

IntercorticalTransfer of Memory

If a cat or monkeyis conditioned to

respond to avisual stimuluswith one eyecovered and thentested with theblindfoldtransferred to theother eye, itperforms theconditionedresponse. This istrue even if theoptic chiasm hasbeen cut, making the visual inputfrom each eye goonly to the

ipsilateral cortex .

In split-brainanimals(sectioned opticchiasma, ant. andpost. commisureand corpuscallosum), nomemory transferoccurs.

Parital callosalsectionexperimentsindicate that thememory transferoccurs in theanterior portion of the corpuscallosum. Similarresults have beenobtained in

humans in whomthe corpuscallosum iscongenitallyabsent or inwhom it has beensectionedsurgically in a neffort to controlepileptic seizures.(neural coding forremembering with one eye whathas been learnedwith the other has beentransferred to theopposite cortexvia thecommisures)

Functions of the 3 major association areas [There are othermodels showing more elaborate subdivisions of thedifferent sensory, motor, and association cortices. Formore, see section VI. ANNEX, Major Functional Areas of theCerebral Cortex]:a) Prefrontal association area (also known as the frontallobe association area, anterior association area orprefrontal cortex) rostral to the premotor area; concernedwith motor planning, language production, judgement(including control of emotions). Also known as a centralexecutive for working memory and other coordinating functions, including receiving inputs from the rest of thecerebral cortex.b) Parietal-occipital-temporal association area (alsoknown as the posterior association area) between thesomesthetic and visual cortices, extending into posteriorportion of temporal lobe; links several sensory modalitiesfor visuo-spatial perception (representational hemispheremainly) and language (categorical hemisphere mainly).

c) Limbic association area (sometimes called also asthe temporal association area) also known as the limbiccortex along the medial edge of the cerebral

hemisphere, from the lower portion of the temporal lobe tothe limbic system; concerned with emotions and memoryformation. This area is associated with the limbic system(see Neurobiology of Instincts and Emotions, previoustopic.)

II. HEMISPHERIC SPECIALIZATION and the CATEGORICALHEMISPHERE: COGNITIVE ASPECTS of LANGUAGE;MATH LOGIC (NEURAL CIRCUITRY of LANGUAGE)

A. LANGUAGE is one major fundamental processin which man differs biologically from animals

Since no experimental animal has highlydeveloped language skills, the study of language isdifficult. There are no simple anatomic differencesbetween the brains of man and other animals toaccount for language, yet subtle differencesbetween the two hemispheres of mans brain doexist and are related to the fact that, in adults,language functions occur predominantly in the leftdominant hemisphere

B. LANGUAGE is separable in two components:conceptualization and expression. These twocomponents have neuroanatomical bases (Seeneural circuitry of language at the last page)

C. Description of Language-related Areas in theCatergorical Hemisphere (in majority, the LeftHemisphere)

**Generally, the left hemisphere is involved in: cognitiveaspects of Language, Math, Logic.

**Language related structures and functions (lefthemisphere); Language Disorders arising from Lesions:[ APHASIAS abnormalities of language functions (not due


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to defects of vision, hearing nor motor paralysis); Lesionscommonly due to embolism or blood clot in cerebral bloodvessel. The neurological literature is rich in informationabout other effects (note that effects on other primarymotor-sensory functions are not included for lack of spaceand focus)]

Structure Function Effects of Lesion/Ablation

Angular gyrus(Area 39)

Processes andinterprets visualinformation priorto transmission toWernickes area

ANOMIC APHASIA difficulty inunderstanding written language(dyslexia or wordblindness) orpictures, becausevisual informationis not processedand transmittedto Wernickesarea.

Wernickes Area(Area 22, leftsuperior posteriortemporal lobe)

Comprehensionof visual andauditoryinformation

FLUENT APHASIA

ArcuateFasciculus

ConnectsWernickes areawith Brocas area

CONDUCTIONAPHASIA (alsotype of Fluent orReceptive orSensory Aphasia)

Brocas Area(Area 44, 45 inLeft frontal

cortex)

Expressive areafor speech

NONFLUENTAPHASIA (alsocalled expressive

or motor aphasia)PlanumTemporale (left);(left superiortemporal gyrus)

This is bigger inleft hemispherethan in right-handedindividuals;involved inlanguage-relatedauditoryprocessing

The assymetry iseven larger in

musicians andothers withperfect pitch.

Left Temporallobe

Area 8 (L)- Lesions: inabilityto retrieve namesof places andpersons (but

Areas 18, 20, 21(L)

Part of a ventral(inferior temporal)pathway

preserves abilityto retrievecommon nouns,verbs andadjectives)

-Lesions: object

agnosia especially on lefthemisphere

Two Lefthemisphere areasfound associatedwithmathematicalability

Left frontal lobe concerened withnumber facts andexact numebrs.

BilateralInfraparietal sulci(parietal lobe) concerned withvisuospatialrepresentationsof numbers andfinger counting.

Forms of Acalculia(impairment of mathematicalability arising from lesions inleft (or right)hemisphere:

1. Left FrontalLobe lesionsresults in aselectiveimpairment of mathematicallyability

2. Bilaterallesions of intraparietal sulci:anotherimpairment of mathematicallyability also results

**Note: Stereognosis functions also exist in left posteriorparietal cortex (somatosensory association area) for thecontralateral side of body, with corresponding deficits(astereognosis) after lesions.

STRUCTURES concerned with expressve functions of language are: Brocas Area, Structures associated withPhonation, Articulation and Expression of Language (bodyand sign language)

STRUCTURES concerned with RECEPTIVE FUNCTIONS of Language: Wernickes Area, Visual and Auditory Pathways

GLOBAL APHASIA type of aphasia that involves bothreceptive and expressive functions. Speech is scant as wellas nonfluent

y Unable to speak or comprehend language

y They cannot read, write, repeat, or name objects.


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y Lesion in the entire perisylvian region, therebycompromising both Brocas and Wenickes areasand the Arcuate Fasciculus.

y Symptoms include right hemiplegia, righthemisensory deficit and usually right homonymoushemianopsia. Usually these are the bedriddenpatients: they can only open their eyes but cannottalk, comprehend, and follow commands.

WRITING IS ABNORMAL IN ALL APHASIAS IN WHICHSPEECH IS ABNORMAL. Below is another model of a neuralcircuit of language processing (Petersen s model, 1988) .(Deaf- mutes trained in sign language who suffer damageto their language-related left hemishere also have animpairment of their sign language abilites. )

(see last page for bigger illustration)

Other known :higher functions of the Categoricalhemisphere:

Left / Categorical hemisphere also involved inprocessing mathematical operation; effectsof lesions on the angular gyrus- also produces Acalculia

- helps processes attentional focus on detailsof an image (local shifts in attention); lesions will result inloss of this ability. (Compare with the visuo-spatialprocessing functions of right hemisphere).

III. HEMISPHREIC SPECIALIZATIONand theREPRESENTATIONAL HEMISPHERE; VISUO-SPATIALPROCESSING, AFFECTIVE COMPONENTS of LANGUAGEand other functions.

GENERALLY, the RIGHT HEMPISPHERE is involved inspatial abilities, face recognition, visual imagery, music(although recent researchers say that musicalfunctions shared by both hemispheres.), as well as theaffective components (prosody) of language (prosody-elements of stress, pitch and rhythm).

Representational Hemisphere: Non-dominant (in

majority, the Right hemisphere). Noted below are majorfunctions as far as higher cortical association visuo-spatial processing (object recognition) is concerned , aswell as some affective components / emotionalcomprehension of language. In general, though notdiscussed here in detail, the right hemisphere seem toexercise dominance over emotions and all aspects of social-emotional intelligence .This is due to its stronger

connections to the limbic system.The neurologicalliterature is rich in information about other effects(note that effects on other primary motor-sensoryfunctions are not included). Other authors may haveslightly different locations for the lesions.

Representational or right hemisphere also involved inprocessing mathematical operation; effects of lesions onthe angular gyrus- also producesAcalculia.Representational or the right hemisphere also helpsprocesses attentional focus on over-all pattern of an image(global shifts in attention); lesions will result in loss of thisability. Compare with the visuo-spatial function of lefthemisphere focusing on details of object/ image.

(Stuttering associated with right cerebral dominance, andwidespread activity in cerebral cortex and cerebellum.)


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IV. SUMMARY of MAJOR ASPECTS OF HEMISPHERIC SPECIALIZATION (LATERALIZATION) and COMPLEMENTATION

This is as far as language and visuo-spatial processing functions are concerned; some aspects of emotions are also noted.(Note that there are other differences not noted here, but abundant in the neurological literature. Other authors may indicateslightly different location of lesions depending on source of scientific papers, but within the affected cortical association area.)


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**the text below the line Perception (drawing by patient) is Left hemisphere functions dominate after right hemisphere.

V. THE COGNITIVE FUNCTIONS OF CEREBROCEREBELLUMS AND BASAL GANGLIABasal Ganglia: The caudate nucleus, possibly because of its frontal cortical connections, have some cognitive roles. Lesions of the caudate nucleus disrupt performance on tests involving object reversal and delayed alternation. The right caudate nucleusseem to be involved in language processing, as shown by evidence where lesions produce a dysarthric form of aphasia thatresembles but different from Wernickes aphasia.Cerebrocerebellum (neocerebellum): involved in planning and programming movements, together with the motor cortex andassociated frontal areas.

The cerebellum seem to be also involved with pure cognitive tasks independent of motor functions: a patient damaged in theright cerebellum (due to a blocked posterior inferior cerebellar artery) could not learn a word association task. Also, it wasobserved in other subjects using magnetic resonance brain imaging technique that the dentate nucleus increased its activitywhen subjects were required to evaluate sensory information consciously.


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VI. ANNEX: MAJOR FUNCTIONAL AREAS OF THE CEREBRAL CORTEX (see also section I. C)

WERNICKEs AREA the auditory association area (Area 41 and 42) of the categorical hemisphere is located here

BROCAs AREA premotor association area is located here

PARIETAL-OCCIPITAL-TEMPORAL association area - association area specialized for visuo-spatial perception that is located inthe representational hemisphere

PREFRONTAL ASSOCIATION AREA function as the Central Executive or the working memory.

OTHER INTELLECTUAL FUNCTIONS of PREFRONTAL CORTEX in HUMANS

1. Make forecasts/predict events based on analysis2. Plan for the future3. Delay action in response to incoming sensory signals4. Consider consequences of motor actions5. Solve complex problems legal, mathematical, philosophical

6. Ethnical behavior higher control of limbic responses

LESIONS in the PREFRONTAL CORTEX and PREFRONTAL LOBOTOMY results in:

1. Inability to solve Complex problems2. Inability to string together consequential tasks to reach specific goals3. Decreased aggressiveness4. Loss of ambition


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5. Lack of social inhibition with sexual and excretory behavior6. Comprehend language, speak but unable to carry through a conversation7. Mood swings8. Purposeless execution of motor tasks learned in life

Figure 1: A region at the posterior end of the superior temporal gyrus called Wernicke's areais concerned with comprehension of auditory and visual information. It projects via the arcuate fasciculus to Broca's area (area 44) in the frontal lobe immediately in

front of the inferior end of the motor cortex. Broca's area processes the information received from Wernicke's area into adetailed and coordinated pattern for vocalization and then projects the pattern via a speech articulation area in the insula to themotor cortex, which initiates the appropriate movements of the lips, tongue, and larynx to produce speech. The probablesequence of events that occurs when a subject names a visual object is shown in the image above (lower right) The angulargyrus behind Wernicke's area appears to process information from words that are read in such a way that they can be convertedinto the auditory forms of the words in Wernicke's area.


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Figure 2. Take note that the Right (representational) hemisphere is concerned with the affective component language, calledprosody (the patterns of rhythm and sound used in poetry). Expressive aprosodia (also known as motor aprosodia or Dysprosody)results from lesion in the Right frontal Cortex. Manifestations include flat tone of ones own voice and gestures (no emotionalfeelings). This mirrors Brocas Aphasia on the left side. Receptive aprosodia (also known as Sensory Aprosodia or Dysprosody)results from lesion in the right posterior parietal cortex which manifests as inability to comprehend prosody. This also mirrorsWernickes aphasia on the left side. An example is the inability to comprehend a joke.


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Below is a table showing a number of observed lesion effects of some right hemisphere cortical association areas showing some resulting agnosias, as well as effects on affective components (prosody) of language (right hemisphere). Fore brevity, onlya few agnosias affecting some of the sensory association areas are shown. A listing of various apraxias(inability to voluntarilycarry out actions upon command, with intact primary sensory and motor pathways) have not been included in the table.[Agnosia - inability/ difficulty recognizing certain features of a sensory stimuli, despite intact primary sensory cortex and specificascending pathways.]

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Hemispheric Organization