Content area
Full text
Key Words network, computation, model, excitation, inhibition
Abstract We explore the extent to which neocortical circuits generalize, i.e., to what extent can neocortical neurons and the circuits they form be considered as canonical? We find that, as has long been suspected by cortical neuroanatomists, the same basic laminar and tangential organization of the excitatory neurons of the neocortex is evident wherever it has been sought. Similarly, the inhibitory neurons show characteristic morphology and patterns of connections throughout the neocortex. We offer a simple model of cortical processing that is consistent with the major features of cortical circuits: The superficial layer neurons within local patches of cortex, and within areas, cooperate to explore all possible interpretations of different cortical input and cooperatively select an interpretation consistent with their various cortical and subcortical inputs.
INTRODUCTION
The enormous strides made in understanding the formation and operation of the neocortical circuits have been matched by the detailed analyses of the cellular and synaptic physiology of the elements that make up the neocortical circuits. Rapid advances in theory have also begun to clarify the nature of the computations carried out by the neocortical microcircuits. There are now many different models of cortical circuits, based on experimental data or theoretical considerations. Perhaps unsurprisingly, given their different explanatory and descriptive purposes, these model circuits differ greatly in form and content. For historical reasons, most biologically defensible circuits rely heavily on data from cat and primate visual cortex, but cell types and patterns of connections have also been described in many other cortical areas, with the contribution from rodent somatosensory cortex being perhaps the most prominent in recent years.
Here we explore to what extent the neocortical circuits discovered in primary sensory areas generalize, i.e., to what extent can neocortical neurons and the circuits they form be considered as canonical? A similar question has been applied to every aspect of the vertebrate brain and spinal cord, and it is especially relevant to questions of evolution, development, and homology of form and function. Most reasonable people would agree that evolution has been conservative, so one is not surprised to find close similarities in basic organization across vertebrate brains. At another level, one is not surprised to find that the neocortices of different mammals...