Responses of cat auditory cortical neurons to amplitude-modulated noise

Swarbrick and Whitfield [J. Physiol. 224, 68–69 (1972)] found a small minority of units in cat primary auditory cortex whose discharge rates appeared to be determined by the symmetry of the stimulus envelope, independent of stimulus duration. This phenomenon was examined in greater detail in the present study. Tungsten microelectrodes were used to record from primary cortical cells in unanesthetized cats. Noise bursts of 4‐, 40‐, 100‐, and 300‐msec duration were used, and the rise‐time/fall‐time ratio was systematically varied for each burst duration. Discharge rates of a few units appeared to preserve information about stimulus envelope, in that the preferred rise‐time/fall‐time ratio was constant with 40‐ and 100‐msec noise bursts. However, contrary to the observations of Swarbrick and Whitfield, this constancy did not extend to 4‐msec bursts. Preferential responses to stimulus shape, when they occurred, were relatively independent of stimulus repetition rate. [Work supported by the Nuffield Foundation.]