Cortical Response to Stimulation of the Optic Nerve

Abstract

In the cortex of the rabbit a small area can occasionally be found that is supplied by one artery and one vein. Such a region can thus be isolated by incisions except for the tongue of tissue where the vessels enter, without serious interference with the blood supply. A metal plate slipped under this tissue and connected to ground serves as an indifferent electrode, and the end of a fine wire resting on the cortical surface serves as a test electrode. When the region so isolated is not active no record is picked up from activity in the rest of the cortex. In 2 cases such a preparation has shown activity, and its pathway could be traced via the tongue of intact tissue. The activity consisted of a succession of wavelike action potentials, about 3 per second, lower than those of the adjacent intact cortex and much less complex. The rotating interrupter of the oscillograph apparatus was adjusted to a speed almost synchronous with these waves, but slightly slower, so that successive waves appeared to progress slowly across the screen. If a stimulus is sent in to the tissue at each revolution of the interrupter, it will fall later and later in successive waves. When stimulated during the negative phase or immediately afterward, no response is elicited, the response becoming larger the later the stimulus falls in the cycle. The response consists of a wave but little shorter than the spontaneous wave, and inhibits the following wave, in which case there is a compensatory pause, but it does not otherwise alter the rhythm which is imposed from without the circumscribed region. The response to stimulation is too protracted to be assignable to nerve fibers directly stimulated, and is presumably due to nerve cells.