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Abstract

Peculiarly, at the same time as modern psychologists are becoming more and more
cognitive, modern views of the cortex seem to turn away from the global aspects of
cortical function in favour of a description in terms of columns and modules, functional
units much finer even than the areas and subareas of the old architectonic school.
We are faced with the question of what holds the modules together when a global
thought is organized in the brain, or even a multisensory perception. Fortunately,
we are not compelled to take the extreme view that would relegate the integrative
action to extracortical structures, with the cortex itself as a passive, compartmentalized
reference file. There are enough synapses in the cortex (1011 in the mouse, 1014 in
man) which can hardly serve any other purpose that that of dynamic interaction of
elementary or complex percepts. How many of these synapses are between neurons
within a “module,” how many of them link neighbouring modules and how many link
modules far apart? These are questions to which our statistical considerations of
cortical structure are addressed. The synapses between cortical neurons vastly outnumber
the synapses between afferent fibers and cortical neurons. Most of these
synapses are between pyramidal cells and are probably excitatory. Synapses between
neighbours are probably not more numerous than those between distant elements.
The influence of a single pyramidal cell onto another is probably very slight, so that
strong effects must be mediated by groups of active neurons. All of this points to the
cortex as the place where “cell assemblies” in the sense of Hebb are organized.