Cerebral cortex, primary cortical areas http://controlmind.info/human-brain/right-and-left-brain Mark Kozsurek, M.D., Ph.D. mark@kozsurek.hu ED II., 07/10/2014

Ontogenesis of the cerebral cortex In a broader sense the pallium (or brain mantle) is the wall of the telencephalic vesicles and consists of both gray and white matters. As the telencephalon grows, it divides into paleopallium, archipallium and neopallium. The gray matter of these parts contributing to the hemispheric surfaces are summarized as paleocortex, archicortex and neocortex, respectively. (Note, that this classification is a bit obsolete, as new concepts appear year-by-year, but many of these also disappear without being confirmed.)

Phylogenesis of the cerebral cortex During the phylogenesis of Mammals the proportion of the paleocortex and the archicortex decreased, while the neocortex became dominant occupying almost the whole surface of the brain. CORTEX Allocortex Isocortex (less than 6 layers) 6 layers Paleocortex Archicortex Not the total number of the layers, but the number of neuronal layers matters!

Paleocortex: the oldest cortical area of the telencephalon which contains 3 to 5 layers of neuronal cell bodies. Paleocortex includes the olfactory bulb, olfactory tubercle (approx. at the anterior perforated area) and the piriform cortex (approx. the uncus and the anterior part of the parahippocampal gyrus). All those cortical and non-cortical areas which are related to the sense of smell are summarized as the rhinencephalon or olfactory brain. Archicortex: constituted by 3 to 4 layers of neurons and includes the hippocampus and related structures (dentate and fasciolar gyri, indusium griseum). Neocortex: occupies approx. 90% of the total cerebral hemispherial surface. 6 layers of neuronal cell bodies are present.

1. Paleocortex http://www.the-scientist.com/?articles.view/articleNo/37607/title/Scent-Sorting/ http://www.nature.com/nrneurol/journal/v8/n6/full/nrneurol.2012.80.html

2. Archicortex What you see in the microscope and the neuronal connections in the background...

Schaffer’s collateral fimbria CA3 GABAergic inhibitory neurons: 1. stellate cells (axo-dendritic) 2. basket cells (axo-somatic) 3. chandelier cells (axo-axonic) Schaffer’s collateral fimbria CA3 1. 2. 3. mossy fibre granule cells in the dentate gyrus CA2 perforant path from entorhinal cortex pyramidal cells CA1

fimbria CA3 mossy fibre CA2 str. moleculare Schaffer’s collaterals str. lacunosum str. radiatum perforant path In CA3 a str. lucidum containing mossy fibres is also present between str. pyramidale and radiatum. str. pyramidale str. oriens alveus CA1

3. Neocortex Molecular layer Outer granule cell layer Outer pyramidal layer Inner granule cell layer Inner pyramidal layer Plexiform layer

PC: pyramidal cell, SSC: spiny stellate cell, BPC: bipolar cell, DBC: double bouquet cell, ChC: chandelier cell, MC: Martinotti cell, LBC: large basket cell, SBC: small basket cell, NBC: nested basket cell, NGC: neurogliaform cell, BTC: bitufted cell (dendrites in red and axons in blue) There are much more types of neurons in the neocortex than it is suggested by silver-impregnated specimens. And which neuron should be considered as a separate group?

The most characteristic cell type of the cerebral cortex: the pyramidal cell. Both its apical and basal dendrites posses spines and the axon arrises from the base of the conical cell body. http://cercor.oxfordjournals.org/content/15/6/802/F1.expansion

Functional units of the cortex: cortical columns each column is approx. 200-300 µm wide and 2.5-3.0 mm tall (as thick as the cortex) each cortical column contains approx. 5000 neurons and altogether 2 million such moduls constitute the human cortex (1000 columns in rats, 1 million in monkeys) neurons predominantly contact other neurons within the same column (vertical communication) each modul communicates with 100-200 other columns

Specific afferents from sensory organs through the thalamus mainly terminate on spiny stellate neurons in lamina IV. Their axons ascend into lamina I and synapse with the apical dendrites of pyramidal cells representing the output of the cortical module. Corticocortical afferents reach almost all the layers of the cortical columns and synapse directly with pyramidal cells. Importance of inhibitory inter-neurons increases close to the margins of cortical columns as they inhibit lateral spreading of neuronal activity, thus, isolate adjacent columns from one other.

Different inhibitory interneurons terminate on distinct parts of pyramidal cells.

Connections among cortical modules Thalamocortical (specific) inputs terminate in lamina IV and make this layer thick in sensory cortical areas. Corticocortical connections arise from lamina III pyramidal cells and terminate with extensively branching endings along the whole thickness of the target column. Long descending motor pathways are mainly constituted by the axons of lamina V pyramidal cells. This is why this layer dominates in motor cortical areas. Lamina VI sends axons back to the thalamus (corticothalamic projection). Inhibitory neurons block lateral spreading of electric neuronal activity.

granular cortex / koniocortex agranular cortex

Cortical fields of Brodman Brodmann, 1909 52 areas of the neocortex have been distinguished according to morphological parameters such as the thickness of layers, types and densities of different cells, etc. Later became obvious that cortical fields described by Brodman are not only morphologicaly but also functionally distinct and have their own roles in different processes.

Motor cortical fields primary motor area (Br4): Betz cells, pyramidal tract premotor area (dorsolateral Br6) supplementary motor area (medial Br6) frontal eye field (Br8): voluntary eye movements Broca’s motor speach center (Br 44, 45) Sensory cortical fields primary somatosensory area (Br 3, 1, 2)

Visual cortical fields primary visual cortex (Br 17, striate area) termination of optic radiation: Gennari’s line secondary visual cortex (Br 18) tertiary visual cortex (Br 19) Auditory cortical fields primary auditory cortex (Br 41) secondary auditory cortex (Br 42) Wernicke’s speach area (Br 22, 39?, 40?)

As a rule of thumb: Primary cortical areas: site of origin of descending motor pathways and sites of termination of ascending sensory pathways. Secondary, tertiary cortical areas: association areas, information processing, memory (visual, auditory, etc.) Note the large extension of cognition- and vision-related areas!

Activity of the cerebral cortex - ARAS

Hemispheric asymmetry – language areas Due to the decussation of large ascending sensory and denscending motor pathways hemispheres feel and move the other side of the body, but in spite of this, the two hemispheres are not completly symmetrical. Dominant: verbal, logical, abstract, analyzing, planning, expressing Subdominant: non-verbal, working with images, synthesizing, sensing Right-handed people: 96%: language areas in the left hemisphere. Left-handed people: 70%: on the left, 15%: on the right, 15%: on both sides.

Where are Wernicke's and Broca's Language Areas? Superimposition of various definitions of Wernicke's and Broca's areas on a standard anatomical drawing of the human left hemisphere.

Thank you for your attention!