Conditioning of the occipital alpha rhythm in man.

Abstract

The depression or blocking of the rhythmic synchronized electrical activity of the occipital cortex in response to visual stimulation in man was used as an unconditioned response. Pure tones between 400 and 700 d.v. per sec. were used as conditioned stimuli. The blocking of the occipital a rhythm to sound was observed after about 10 paired presentations of sound and light, an unstable conditioned response. With more trials it was possible to establish cyclic, delayed, trace, differential, differential delayed, and backward conditioning. Backward conditioning was established only when the initial light stimulus was allowed to overlap the succeeding sound but not when an interval was allowed to elapse between the unconditioned and conditioned stimuli. After several trials with the backward conditioning technique a sound stimulus reestablished the a rhythm if be used as a measure of the polarization of the plasma membrane at the node. A nerve impulse blocked by narcosis will nevertheless diminish the threshold of the first node beyond the blocked region. The action potential diminishes to about half of its value each time a non-excitable node is passed by the impulse. The potential at the plasma membrane at the nodes consists of 2 phases. During the first phase of about 0.5 msec. a constant potential of 90 mvolt is maintained, while during the second phase this potential diminishes at a constant rate. For the excitation of a single node, the all-or-none law is valid. Narcosis gradually diminishes to zero the action potentials produced at the plasma membranes. The myelin sheet is not a perfect electric insulator. The internodal parts of the fibers are not excitable.