Cerebral Cortex

Cerebral Cortex  The layer of gray matter covering the entire surface of cerebral hemisphere Migration of neurons from inner mantle layer of neural tube Accommodates enormous number of neurons - Large surface area accommodates more neurons than deep nuclei - Gyri and sulci also increase surface area - Laminar organization also accommodates enormous number of neurons

Numerical Data Cerebral Cortex  Total surface area: 2200 cm2 (2.5 ft2) about 1/3 ------ surface area about 2/3 ------ hidden in the sulci  Thickness: 1.5 mm (V I) - 4.5 mm (M I) Generally, thickest over the crest of the convolution and, thinnest in the depth of sulci  Weight: 600 gm (40 % of total brain weight) 180 gm --------- neurons 420 gm --------- glial cells

Numerical Data Cerebral Cortex  Number of neuronal cells in cerebral cortex neurons ----------- 10-15 billion glial cells ---------- 50 billion  Estimation of number of cortical neurons von Economo and Koskinas (1925) 14.0 billion Shariff (1953) 6.9 billion Sholl (1956) 5.0 billion Pakkenberg (1966) 2.6 billion

Subdivision of Cerebral Cortex Allocortex Archicortex (Archipallium) Palaeocortex (Paleopallium) Isocortex Neocortex (Neopallium) cf. mesocortex, juxtallocortex, mesallocortex

Isocortex – typical 6 layered cortex I. Molecular Layer II. External Granular Layer III. External Pyramidal Layer IV. Internal Granular Layer V. Internal Pyramidal Layer VI. Polymorphic Layer

Histological Organization Cerebral Cortex Histological Organization Cellular Elements 1. Pyramidal Cell - output neuron giant pyramidal cell of Betz 2. Fusiform Cell --- modified pyramidal cell 3. Granular (Stellate) Cell basket cell, double bouquet cell, bipolar cell, chandlier cell, neurogliform cell 4. Horizontal Cell of Cajal (Retzius-Cajal cell) 5. Cells of Martinotti

Cerebral Cortex 1. Pyramidal Cell 2. Fusiform Cell 3. Granular (Stellate) Cell 4. basket cell 5. double bouquet cell 6. chandlier cell 7. neurogliform cell 8. Horizontal Cell of Cajal 9. Cells of Martinotti a: axon

II. External Granular Layer III. External Pyramidal Layer I. Molecular Layer II. External Granular Layer III. External Pyramidal Layer Line of Kaes-Bechterew IV. Internal Granular Layer Outer band of Baillarger - Line of Gennari in area 17 V. Internal Pyramidal Layer Giant pyramidal cell of Betz Inner Band of Baillarger VI. Polymorphic Layer Golgi Nissl Weigert

Cortical Afferent Fiber 1. corticocortical fiber association fiber commissural fiber 2. thalamocortical fiber - specific and non-specific 3. extrathalamic subcortical fiber cholinergic fiber - acetylcholine basal nucleus of Meynert mesolimbic dopaminergic fiber - dopamine ventral tegmental area serotonergic fiber – serotonine - raphe nuclei norepinephrinergic fiber - norepinephrine nucleus locus ceruleus

Cortical Afferent Fiber 1. association fiber 2. commissural fiber 3. specific thalamocortical fiber 4. non-specific

Cortical Efferent Fiber 1. Corticofugal Fiber - Projection Fiber corticostriate fiber corticothalamic fiber corticorubral fiber corticotectal fiber corticopontine fiber cortico-olivary fiber corticobulbar fiber corticospinal fiber 2. Corticocortical Fiber Association fiber Commissural fiber

Cortical Efferent Fiber 5. association fiber 6. commissural fiber 7. corticostriate fiber 8. corticorubral fiber corticopontine fiber corticobulbar fiber 9. corticospinal fiber corticotectal fiber 10. corticothalamic fiber

Columnar Cortical Unit and Cortical Circuitary A. pyramidal neuron B. excitatory granular cell C. inhibitory 1. afferent fiber 2. efferent fiber 3. corticothalamic fiber

Regional Variation of Cortical Lamination A. Homotypical isocortex ------- association cortex B. Heterotypical isocortex 1. granular cortex --- primary sensory cortex V I (17), S I (3), A I (41) 2. agranular cortex --- motor cortex M I (4), PM (6)

Functional Localization of Cerebral Cortex  Phrenology of Gall and Spurzheim  Clinical evidences Broca’s area (1861) Jacksonian epilepsy (1864)  Experimental evidences Fritsch and Hitzig (1870) --- motor cortex von Gudden (1870) ---- visual cortex Ferrier (1873) ---- auditory cortex

PET (positron emission tomography) scan

Morphological Classification of Cortical Areas  based on cytoarchitectonic studies  Campbell (1905) -------- about 20 areas  Brodmann (1909) ------ 47 areas - most popular  Vogt and Vogt (1919) - over 200 areas  von Economo (1929) -- 109 areas

Brodmann’s cytoarchitectorial map (Lateral surface)

Brodmann’s cytoarchitectorial map (Lateral surface)

Functional Localization of Cerebral Cortex Sensory area primary sensory area secondary sensory area Motor area primary motor area secondary motor area supplementary motor area Association area parietal, occipital and temporal cortex - conceptual elaboration of sensory data prefrontal (frontal) cortex - judgement, foresight

Sensory Areas Somesthetic Area (Somesthesia) S I, S II Visual Area (vision) V I, V II Auditory Area (Hearing) A I, A II Vestibular Area (Equilibrium) Gustatory Area (Taste) Olfactory Area (Smell)

Somesthetic Area S I ----- 3, 1, 2 (postcentral gyrus) afferernts: ventrobasal complex (VPLc, VPM) discrimination of position and intensity of sensation S II ---- superior bank of lateral fissure no clinical disorders Somesthetic Association Cortex ------- 5, 7 (parietal lobule, precuneus) afferents: S I, LP of thalamus integration of geneal sensation with past experience tactile agnosia, astereognosis

Sensory Homunculus

Secondary Somesthetic Area (SII) superior bank of lateral fissure

Visual Cortex V I ----- 17 (striate cortex - line of Gennari) greatly thickened outer band of Baillarger heterotypical isocortex afferent: LGd of thalamus visual field defect: homonymous quadranopsia and macular sparing V II ---- 18, 19 (visual association area) afferents: V I, pulvinar of thalamus integration of vision with past experience visual agnosia cf. occipital eye field

Visual Areas

Visual association areas (color) Face recognition Perceive Facial Expression

Auditory Cortex A I ----- 41, 42 (trannsverse temporal gyrus of Heschl) heterotypical isocortex afferents: MGv of thalamus - core projection slight diminution in auditory acuity A II ---- 22 (Wernike's area of original connotaion) not well-defined afferents: non-laminar part (MGm, MGd) – belt projection A I auditory agnosia - sensory aphasia

Other Primary Sensory Areas Vestibular Area Area 3a and 2v of S I afferents: VPLo [superior temporal gyrus anterior to A I] Gustatory Area Area 43 (inferior end of postcentral gyrus) afferents: VPMpc Olfactory Area Piriform Lobe - Limbic System

Motor Areas primary Motor Area (M I) Premotor Area (PM) Supplementary Motor Area (SMA) Frontal Eye Field

Motor Homunculus

Primary Motor Area M I ------- 4 precentral gyrus of lateral surface anterior part of paracentral lobule heterotypical agranular cortex giant pyramidal cell of Betz afferents: premotor area, SMA, S I VLc, VPLo of thalamus Motor Homunculus Upper Motor Neuron (UMN) syndrome

Other Motor Areas Premotor Area (PM) ------ lateral surface of 6 afferents: VLc, VPLo of thalamus from cerebellum Supplementary Motor Area (SMA) -------------------------- medial surface of 6 afferents: VLo, Vapc of thalamus from basal ganglia Frontal Eye Field ---------- 8 voluntary tracking movement

Brodman’s Map of Motor and Sensory Areas

Association Areas Language Areas ----- 22, 39, 40, 44, 45 Posterior Parietal Association Area ------ 5, 7 (39, 40) body image Temporal Association Area ------ 20, 21, 37, 38 (22) multisensory integration, conceptual ideation Prefrontal Association Area ----- 9, 10, 11, 12, 46, 47 (44, 45) judgement, foresight, personality

Order of Cortical Maturation 1 3 3 2 1 2 1 3 Order of Cortical Maturation

Disorders of Association Cortex  Agnosia Tactile agnosia Visual agnosia Alexia Auditory agnosia  Apraxia  Aphasia Wernicke’s (receptive) aphasia Broca’s (Motor) aphasia conduction aphasia global aphasia

Apraxia The inability to execute a voluntary motor movement despite being able to demonstrate normal muscle function.

Language Areas Sensory Language Area (Wernike's area) ---- 22, 39, 40 Receptive Aphasia - area 22 defect in comprehension, good spontaneous speech Anomic Aphasia - word finding difficulty Jargon aphasia - fluent, but unintelligiable jargon 39 (supramarginal gyrus), 40 (angular gyrus) Superior Longitudinal Fasciculus Conduction Aphasia good comprehension, good spontaneous speech poor repetition, poor response Motor Language Area (Broca’s area) --- 44, 45 Motor Apahsia good comprehension, no speech

Language Areas (Geschwind Model)

Paul Broca (1824-1880) Carl Wernicke (1848-1905)

PET (positron emission tomography) scan

Composite radioisotope brain scan

Cerebral Dominance (Lateralization, Asymmetry) Dominant Hemisphere Language – speech, writing Calculation Non-dominant Hemisphere Spatial Perception (3D subject) Singing Playing musical instrument

Language Speech Writing Calculation 3D perception Singing Playing Musical instrument

(split corpus callosum) Split Brain Commissuratomy (split corpus callosum) Two minds in one brain?                                             Roger Sperry (1913-1994) 1981 Nobel Laureate

Prefrontal Association Areas Frontal Granular Cortex Lateral Prefrontal Association Area ------ 9, 10, 46 judgement, foresight, problem solving Orbitofrontal Cortex ------ 11, 12, 47 emotion, olfaction, personality  Case of Phineas Gage  Prefrontal Leucotomy of Moniz and Freeman

Phineas Gage (1823-1861, accident in 1848)

Phineas Gage’s lesion reconstructed (H. Damasio and R. Frank, 1992)

Prefrontal Leucotomy (Frontal Lobotomy) Antonio Egas Moniz

Conceptual Framework of Cerebral Function