Cerebral Cortex – 2 Avinash Bharadwaj ANHB 2217 – 2006

Cerebral Cortex General topography Complex circuitry and ‘cytoarchitecture’ 10 9 – neurons Six types of neurons Local connections (Intracortical circuitry) Long neurons (Principal cells) Commissural and association fibres Projection fibres

Cortex : Neuron Types Principal types Pyramidal Fusiform Retzius-Cajal Basket Stellate Martinotti

Cortex - Layers Molecular External granular External pyramidal Internal granular Internal pyramidal Multiform 5 and 6 – “older” Bands of Baillarger – Outer and Inner Prominent in sensory areas Outer – Stria of Gennari in visual cortex

Basic Features - Circuitry Highly simplified description! Columnar organisation Thalamic afferents Mainly excite stellate cells in layer 4  Pyramidal cells in the same column Basket cells inhibit pyramidal cells in neighbouring columns Association and commissural afferents Reach superficial layers Other afferents reach layers 1, 2, 3. Efferents – “Principal” cells Association, commissural, projection fibres

“Types” of Cortex Phylogenetic scheme Paleo- and archicortex (allocortex) Olfactory and limbic system areas Neocortex (isocortex) Most of human cortex Histological scheme High interneuron population – granular cortex High pyramidal cell population – agranular Brodmann classification Various criteria 52 areas, numbered

Brodmann’s Areas Major areas Sensory Motor Auditory Visual

Functional Localisation General sensory Motor – Frontal lobe and others Auditory – temporal lobe Visual – occipital lobe Language areas Sensory integration Sounds and sights, words and concepts Motor speech area Further details with individual systems!

Localisation… Experimental study Clinical and post-mortem studies Difficulties with both… Recent technology

Localisation and Blood Supply M C A P C A A C A

Cortical Dominance Left Speech and language areas Right Spatial awareness – body and surroundings Non-verbal content of speech Musical abilities Normal functioning requires communication between the hemispheres! Right- or left handedness Not always consistent with hemispheric functions