First, from Boycott and Young (3), “The current conception, on which
most discussions of learning still concentrate, is that the nervous
system consists essentially of an aggregate of chains of conductors,
linked at key points by synapses. This reflex conception, springing
probably from Cartesian theory and method, has no doubt proved of
outstanding value in helping us to analyse the actions of the spinal
cord, but it can be argued that it has actually obstructed the
development of understanding of cerebral function.”
Most observable evidence of learning and memory is extremely complex
and its interpretation full of traps. Learning in its broadest sense
might be detected as a semipermanent change of behavior pattern brought
about as a result of experience. Within that kind of definition, we
can surely identify several distinctly different types of learning,
presumably with distinctly different kinds of mechanisms associated
with each one. But, if we are to stick by our definition of a condition
of semipermanent change of behavior as a criterion for learning, then
we may also be misled into considering the development of a neurosis,
for example, as learning, or even a deep coma as learning.
When we come to consider field effects, current theories tend to get
fairly obscure, but there seems to be an almost universal recognition
of the fact that such fields are significant. For example, Morrell
(16) says in his review of electrophysiological contributions to the
neural basis of learning, “A growing body of knowledge (see reviews
by Purpura, Grundfest, and Bishop) suggests that the most significant
integrative work of the central nervous system is carried on in graded
response elements—elements in which the degree of reaction depends upon
stimulus intensity and is not all-or-none, which have no refractory
period and in which continuously varying potential changes of either
sign occur and mix and algebraically sum.” Gerard (7) also makes a
number of general comments along these lines. “These attributes of
a given cell are, in turn, normally controlled by impulses arising
from other regions, by fields surrounding them—both electric and
chemical—electric and chemical fields can strongly influence the
interaction of neurones. This has been amply expounded in the case of
the electric fields.”
Learning situations involving “punishment” and “reward” or,
subjectively, “pain” and “pleasure” may very likely be associated
with transient but structurally widespread field effects. States of
distress and of success seem to exert a lasting influence on behavior
only in relation to _simultaneous_ sensory events or, better yet,
sensory events just immediately _preceding_ in time. For example, the
“anticipatory” nature of a conditioned reflex has been widely noted
(21). From a structural point of view, it is as if recently active
sites regardless of location or function were especially sensitive to
extensive fields. There is a known inherent electrical property of both
nerve membrane and passive iron surface that could hold the answer to
this mechanism of spatially-diffuse temporal association; namely, the
surface resistance drops to less than 1 per cent of its resting value
during the refractory period which immediately follows activation.