THE CEREBRAL CORTEX Institute of Anatomy, 2nd Medical Faculty R. Druga

NEOCORTEX Laminar pattern – 6 layers Laminar pattern – 6 layers 10 – 20 billion neurons 10 – 20 billion neurons 95 % surface of the hemisphere 95 % surface of the hemisphere

NEOCORTEX, types of neurons Pyramidal neurons Pyramidal neurons Apical and basal dendrites Apical and basal dendrites Dendritic spines Dendritic spines Excitatory (glutamate) Excitatory (glutamate) Homogenous group Homogenous group 60 – 70 % 60 – 70 % Non-pyramidal neurons Non-pyramidal neurons Aspiny Aspiny Heterogenous group Heterogenous group Inhibitory ( GABA) Inhibitory ( GABA) 30 – 40 % 30 – 40 %

Pyramidal neurons Layer V. M I Golgi impregnation

Projection neurons, excitatory, glutamate Long axons Local circuit neurons, inhibitory, GABA Interneurons, short axons

My investigations showed that the functional superiority of the human brain is intimately bound up with the prodigious abundance and unusual wealth of forms of the so-called neurons with the short axons. S. R. y Cajal: Recuerdos de mi vida Interneurons are butterflies of the soul. S.R. y Cajal 1923

Characteristics of layers I.. Molecular layer – local inhibitory interneurons I.. Molecular layer – local inhibitory interneurons II. External granular – association neurons II. External granular – association neurons III. External pyramidal – commissural neurons III. External pyramidal – commissural neurons IV. Internal granular – receives thalamocortical projections IV. Internal granular – receives thalamocortical projections V. Internal pyramidal – projecting neurons (basal ganglia, brain stem, spinal cord V. Internal pyramidal – projecting neurons (basal ganglia, brain stem, spinal cord VI. Multiform layer – corticothalamic neurons VI. Multiform layer – corticothalamic neurons

K.Brodmann, 1907, regions 52 areas

Association areas

Afferent neocortical connections Thalamic nuclei (thalamocortical fibers) Thalamic nuclei (thalamocortical fibers) Amygdala Amygdala Claustrum Claustrum Nc. basalis (Meynert)-cholinergic system Nc. basalis (Meynert)-cholinergic system Hypothalamus Hypothalamus Raphe nuclei (serotonin) Raphe nuclei (serotonin) Locus coeruleus (noradrenalin) Locus coeruleus (noradrenalin) Subst. Nigra (VTA) - dopamin Subst. Nigra (VTA) - dopamin

Excitatory connections in the neocortex Layer 4 – termination of thalamocortical projections Layer 4 – termination of thalamocortical projections Layer 4 – projects to layer 3 Layer 4 – projects to layer 3 Layer 3 – projects to layer 5 Layer 3 – projects to layer 5

Efferent neocortical connections Thalamic nuclei Thalamic nuclei Basal ganglia (striatum, amygdala, claustrum) Basal ganglia (striatum, amygdala, claustrum) Brain stem (pretectal area, tectum, nc. ruber, RF, nuclei of cranial nerves, pontine ncc., nc. gracilis, nc. cuneatus) Brain stem (pretectal area, tectum, nc. ruber, RF, nuclei of cranial nerves, pontine ncc., nc. gracilis, nc. cuneatus) Spinal cord ( corticospinal pathway, interneurons, motoneurons) Spinal cord ( corticospinal pathway, interneurons, motoneurons)

Motor cortical area G. Fritsch and E. Hitzig (1870) demonstrated that electrical stimulation of the dog´s frontal lobe results in contralateral muscular contractions (movements) G. Fritsch and E. Hitzig (1870) demonstrated that electrical stimulation of the dog´s frontal lobe results in contralateral muscular contractions (movements)

Primary motor area M I Precentral gyrus, area 4 Precentral gyrus, area 4 Part of the cortex from which movements are easily produced by electrical stimulation Part of the cortex from which movements are easily produced by electrical stimulation Motor homunculus (overrepresentation muscles of the thumb, hand, face, tongue, somatotopic representation) Motor homunculus (overrepresentation muscles of the thumb, hand, face, tongue, somatotopic representation) Afferents : S I, thalamic VL Afferents : S I, thalamic VL Efferents : basal ganglia, thalamus, (VL) RF, superior colliculus, nc. ruber, RF, pontine ncc., spinal cort Efferents : basal ganglia, thalamus, (VL) RF, superior colliculus, nc. ruber, RF, pontine ncc., spinal cort Control of distal muscles Control of distal muscles Damage produces paralysis of contralateral muscles (namely upper limb, tongue, facial muscles) Damage produces paralysis of contralateral muscles (namely upper limb, tongue, facial muscles)

Premotor area, PM Area 6 Area 6 Somatotopic representation of the body musculature, less precisely organized Somatotopic representation of the body musculature, less precisely organized Efferents – M I, basal ganglia, RF, Spinal cord (influences paravertebral and proximal limb musculature) Efferents – M I, basal ganglia, RF, Spinal cord (influences paravertebral and proximal limb musculature) Afferents – thalamic VA (basal ganglia), S I, Afferents – thalamic VA (basal ganglia), S I, Preparation to move Preparation to move

Supplementary motor area Area 6, medial surface of the hemisphere Area 6, medial surface of the hemisphere Somatotopic organization,less precisely organized Somatotopic organization,less precisely organized Afferents – thalamic VA (basal ganglia), parietal cortex Afferents – thalamic VA (basal ganglia), parietal cortex Efferents – MI, Basal ganglia, RF, Spinal cord Efferents – MI, Basal ganglia, RF, Spinal cord Area is involved in organizing and planning the sequence of muscle activation Area is involved in organizing and planning the sequence of muscle activation

Somatosensory area S I Postcentral gyrus Postcentral gyrus Areas 3a, 3b, 1, 2 Areas 3a, 3b, 1, 2 Afferents : VPL, VPM Afferents : VPL, VPM Efferents : M I, thalamus (VPL, VPM), pontine ncc., nuclei of cranial nerves (V.), spinal cord Efferents : M I, thalamus (VPL, VPM), pontine ncc., nuclei of cranial nerves (V.), spinal cord 3a – signals from muscle spindles 3a – signals from muscle spindles 3b – cutaneous receptors 3b – cutaneous receptors 2 – joint receptors 2 – joint receptors 1 – all modalities 1 – all modalities

Sensory homunculus

LANGUAGE AREAS Broca : patient losses the ability to speak, produces single words, or syllables. Understanding of language is preserved. Often combined with agraphia. Wernicke : sensory or receptive aphasia, spontaneous speech is fluent, but sounds are often put together into meaningless words – „ word salad „. Often combined with alexia – the inability to read.

Auditory cortex Area 41 Area 41 Afferents – auditory pathway (thalamic medial geniculate body) Afferents – auditory pathway (thalamic medial geniculate body) Efferents – thalamus (medial geniculate body), inferior colliculus, associative cortical areas (what and where paths) Efferents – thalamus (medial geniculate body), inferior colliculus, associative cortical areas (what and where paths)

Visual cortex Area 17, granular cortex Area 17, granular cortex Afferents – visual pathway, thalamic lateral geniculate body Afferents – visual pathway, thalamic lateral geniculate body Efferents – thalamus (lateral geniculate body), area 18, 19, parietal cortex, temporal cortex. Efferents – thalamus (lateral geniculate body), area 18, 19, parietal cortex, temporal cortex. Dorsal stream – parietal cortex (where : rods, periphery of retina, area 7) Dorsal stream – parietal cortex (where : rods, periphery of retina, area 7) Ventral stream – temporal cortex (what- colors, form : cones, central area of retina, area 37, inferior. temporal cortex Ventral stream – temporal cortex (what- colors, form : cones, central area of retina, area 37, inferior. temporal cortex

Corpus callosum – transekce

Cerebral cortex All mammals depend on it All mammals depend on it A man without a cortex is almost vegetable, speechless, sightless, senseless (D. Hubel and T. Wiesel 1979). A man without a cortex is almost vegetable, speechless, sightless, senseless (D. Hubel and T. Wiesel 1979). The cortex supports sensory perception, reasoning, planning and execution of behaviors The cortex supports sensory perception, reasoning, planning and execution of behaviors