THE EFFECT OF BRIEF CURRENTS ON AXONS, ESPECIALLY IN RELATION TO THE POSTULATED NONCONDUCTED RESPONSE

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Abstract
Observations have been made to test the existence in normal, medullated frog''s nerve of a local nonconducted response to subthreshold shocks. The expts. include records of spikes of single axons obtained from the stimulating cathode without use of any balancing device. Subthreshold shocks produce no refractoriness and neither block nor slow conduction. The only observable local negativity produced by a subthreshold shock varies directly as the applied voltage. When a conditioning shock is just subthreshold and is followed after a brief interval by a weak testing shock, stimulation occurs early, very nearly at the time of maximum excitation from the conditioning shock. When the conditioning shock is weak, or the separation between the 2 shocks wide, the testing shock predominates and the response occurs at a later time. This change in the time of the response is responsible for the inconstant relation of conditioning shock to latent addition. From latent addition curves information may be obtained as to the temporal configuration of the "local excitatory process." It confirms the views on nerve stimulation by short shocks previously advanced by Blair and Erlanger (1936a). The intensity of the "local excitatory process" appears to vary linearly with the voltage of a subthreshold shock. The temporal configuration of the "local excitatory process" appears to depend in part on the amt. of shunting tissue. There are indications that the excitation from a shock (local excitatory process) has the configuration of the electrotonic potential. In depressed nonconducting medullated nerve, the all-or-nothing response of a single segment is the least obtainable; increasing the strength of stimulation increases the spike through the entrance of additional segment responses.

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