Our measurements indicate that, during the refractory period following
excitation, the surface resistance of iron in nitric acid drops to
substantially less than 1% of its resting value in a manner reminiscent
of nerve membranes (4). Thus, if a distributed or gross field exists
at any time throughout a complex cellular aggregate, concomitant
current densities in locally-refractive regions will be substantially
higher than elsewhere and, if conditions appropriate to dendrite
growth exist (as described above) growth rates in such regions will
also be substantially higher than elsewhere. It would appear that, as
a result, recently active functional couplings (in contrast to those
not associated with recent neural activity) should be significantly
altered by widely distributed fields or massive peripheral shocks. This
mechanism might thus explain the apparent ability of the brain to form
specific temporal associations in response to spatially-diffuse effects
such as are generated, for example, by the pain receptors.
[Illustration: (a)]
[Illustration: (b)
Figure 6—Dendritic structures, living and non-living. (a) Cat dendrite
trees (from Bok, “Histonomy of the Cerebral Cortex,” Elsevier, 1959);
(b) Electrodeposited gold dendrite tree.]