Modification by Strychnine of Response of the Optic Cortex. ∗

Abstract

Stimulation of the optic nerve of the rabbit by a single shock results in a sequence of potential changes recorded from the optic cortex which occupy 1/5 second. At threshold for the response, the first potential is a monophasic surface-positive wave, followed by a surface-negative, and this in turn by a surface-positive deflection. Above threshold, the initial positive wave is covered up by a larger diphasic response (Bartley and Bishop 2 ). Ether depresses this diphasic response, and strychnine increases it differentially (Bartley 1 ), as compared to the sequence initiated by the monophasic wave. Dilute strychnine applied locally to the cortical surface may increase the diphasic component by 500% without any change in the amplitude of later parts of the record. Higher concentrations depress the late components to extinction, and increase the diphasic wave still further. Finally, spontaneous responses occur, first singly, then in trains. Whether recorded from across the whole cortex, or from needles subtending only certain strata, this spontaneous wave duplicates the diphasic response to stimulation both in relative amplitude of the 2 phases and in duration. The spontaneous rhythmic activity which is present before the application of strychnine, decreases and disappears parallel with the disappearance of the later components of the stimulated response. Facilitation to a second response, which accompanies the late surface-positive wave of the normal record, disappears as this component is suppressed by strychnine.

Strychnine thus serves to differentiate 2 sequences of potential, one consisting of the 2 phases of the early diphasic component, lasting about 20 ms., the other consisting of the triphasic sequence of 3 slow waves lasting 200 ms. The latter can be correlated with the normal spontaneous 5 per second rhythm in a number of respects (Bishop 3 ), to the extent that it has been inferred to occupy the same cortical elements.