Potentials evoked by sound in the auditory cortex of the cat

¹ Clinical Neuropharmacology Research Center, National Institute of Mental Health, Bethesda, Maryland; and Department of Neurophysiology, Walter Reed Army Institute of Research, Washington, D. C.

The electrical responses of the auditory cortex of awake, loosely restrained cats were examined with chronically implanted calomel electrodes and d-c recording systems. Stimulation with a single click evoked a complex triphasic response in which a large surface positive potential (duration, 250 msec) followed the classic diphasic response. This second positive wave was absent in natural sleep and under light barbiturate anesthesia. A similar late positive wave of long duration, evoked by a flash of light, was found in the visual cortex. A rapid series of clicks evoked a surface negative shift which was maintained for the duration of the stimulus. A tone or white noise presented for several seconds evoked a negative shift of the same general form. A pure tone of moderate intensity presented simultaneously with a click greatly enhanced the click-evoked response. White noise of moderate intensity presented simultaneously with a click diminished the size of the click-evoked response.