Introduction

A prominent feature of the brain is the apparent diversity of its structure: the distribution of neurons and the way in which their dendrites and axon fibers differ in various brain centers. The pattern of inputs and outputs of each neuron in the brain most probably differs from that of any other neuron in the system, and this possibility clearly imposes constraints on any attempts at generalization. Yet, since its inception, microscopy of the central nervous system (CNS) has involved a sustained effort to define the laws of spatial arrangement and of connectivity distinguishing specific structures. However, the question which naturally arises from the above is whether these structural features may reflect, and perhaps determine, fundamental differences in the mode of operation of distinct brain structures. Alternatively, the possibility may exist that such structural specializations merely represent anatomical ‘accidents of development’, perhaps reflecting phylogenic origin, but playing a functional role which is no more significant than, for example, that of the appendix or the coccygeal vertebrae in man.

It is difficult to provide an answer to this question from the presently available anatomical and physiological data. Although substantial neurohistological data, on one hand, and neurophysiological information, on the other, are available, meaningful correlation of these two sets of data can only be accomplished in very isolated instances. In general, unlike recording from invertebrates, where the simplicity and viability of the nervous system makes it feasible to observe the elements recorded, physiological studies of the mammalian CNS are performed in a ‘blind’ fashion and it is exceedingly difficult to correlate these studies with the microscopical anatomy of the tissue.