THE PRODUCTION OF RHYTHMICALLY RECURRENT CORTICAL POTENTIALS AFTER LOCALIZED THALAMIC STIMULATION

Abstract

Stimulation of medial thalamic regions with a slow series of stimuli set up a recruiting potential of 20 to 35 misc. latency which was widespread in the cortex. This response and the spontaneous 8-12 per sec. burst potentials were similar in the following respects. The distribution and magnitude of the 2 potentials were similar. The recruiting potentials followed accurately at stimulus frequencies near those of the spontaneous 8-12 per sec. activity. At slower frequencies, trains of 8-12 per sec. activity appeared which were out of phase with the stimuli. Faster stimulus frequencies caused a breakdown of the recruited potential and an abolition of the spontaneous potentials during the period of stimulation. The size of the initial recruiting effect was related to the phase of the spontaneous burst at which it was induced. Long continued stimulation at appropriate rates led to a periodic recruitment and de-recruitment similar to the waxing and waning of the spontaneous bursts. Both spontaneous and recruited potentials were recorded from areas of cortex isolated except for their thalamic connections. Neither effect depended, therefore, upon long intracortical connections. Recruited and spontaneous potentials showed essential similarities in behavior when the interaction of various cortical responses was studied. Because of the above considerations it is suggested that the recruited and the spontaneous 8-12 per sec. potentials are identical.