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.] SUMMARY An attempt is being made to develop meaningful electrochemical model techniques which may contribute toward a clearer understanding of cortical function. Two basic phenomena are simultaneously employed which are variants of (1) the Lillie iron-wire nerve model, and (2) growth of metallic dendrites by electrodeposition. These phenomena are being induced particularly within dense cellular aggregates of various materials whose interstitial spaces are flooded with liquid electrolyte. REFERENCES 1. Bok, S. T., “Histonomy of the Cerebral Cortex,” Amsterdam, London:Elsevier Publishing Co., New York:Princeton, 1959 2. Bonhoeffer, K. F., “Activation of Passive Iron as a Model for the Excitation of Nerve,” _J. Gen. Physiol._ =32=:69-91 (1948). This paper summarizes work carried out during 1941-1946 at the University of Leipzig, and published during the war years in German periodicals. 3. Boycott, B. B., and Young, J. Z., “The Comparative Study of Learning,” S. E. B. Symposia, No. IV “Physiological Mechanisms in Animal Behavior,” Cambridge: University Press, USA:Academic Press, Inc., 1950 4. Cole, K. S., and Curtis, H. J., “Electric Impedance of the Squid Giant Axon During Activity,” _J. Gen. Physiol._ =22=:649-670 (1939) 5. Eccles, J. C., “The Effects of Use and Disuse of Synaptic Function,” “Brain Mechanisms and Learning—A Symposium,” organized by the Council for International Organizations of Medical Science, Oxford:Blackwell Scientific Publications, 1961