Extralemniscal activation of auditory cortex in cats

¹ Department of Neurophysiology, Walter Reed Army Institute of Research, Washington, D.C.

Unanesthetized cats exhibit a complex pattern of evoked activity at the cortex lasting up to a second or longer following click stimulation to the ear. Transection of the classical auditory pathway at the level of the brachium of the inferior colliculus does not in any significant way alter this pattern of response. Most important, the onset of the response, if affected at all by the section, is delayed only up to 2 or 3 msec. A more medial pathway of prime importance paralleling the classical auditory projection must therefore be postulated. Conduction in this extralemniscal system is completely blocked by deep barbiturate anesthesia while it is left intact by chloralose anesthesia.