Number of Neurons and Synapses in Primary Visual Cortex

Of all cortical areas, primary visual cortex has been the one to attract the overwhelming attention of neurophysiologists, largely because the stimuli necessary to activate it can be readily offered to an animal in a reproducible fashion to evoke well-defined responses from the constituent neurons. This activity on the part of neurophysiologists has induced neuroanatomists, and more recently neurophysiologists themselves, to examine the neurons present in visual cortex in attempts to ascertain how the various neuronal types are synaptically related to each other and to the extrinsic inputs that impinge upon them. In addition, visual cortex, and in particular area 17 of the rat, has been a favorite object for those interested in the neurotransmitters used by various neuronal types, while in cat visual cortex others have tried to determine how different transmitters affect the response properties of neurons. Much of these data have been presented in Volume 2 of this series.