Conditional control transfer mechanisms in the neocortex: 2. Cytoarchitectural and electrophysiological evidence and predictions.

Abstract Neuroanatomical and electrophysiological evidence appertaining to the model of the neocortex described in the preceding paper is discussed. It is shown that pyramid cells appear to have the properties of the proposed M type cells. There is a considerable body of evidence suggesting that neocortical basket cells are the interneurones which transmit recurrent inhibition from collateral axons of pyramid cells. Hence it is possible to identify the proposed C type cells as basket cells. The pathways transmitting context information from outside the cortex are identified with specific thalamic afferents which terminate on spiny stellate cells in lamina IV which in turn appear to form powerful excitatory synaptic contacts on pyramid cells. The pathways transmitting context information short distances within the cortex are identified with the excitatory recurrent collateral axons of pyramid cells. It is suggested that transmission of context information over longer distances within the cortex is mediated by pyramid cells whose axons project to other cortical areas and terminate in laminae II and III. It is tentatively suggested that these terminals may be on “cellules a double bouquet dendritique” which appear to have strong excitatory projections to neighbouring pyramid cells. A number of neuroanatomical predictions are discussed.