Responses to acoustic stimuli of units in the auditory cortex of awake squirrel monkeys.

The responses of single units in the superior temporal gyrus of awake squirrel monkeys to tone pips, noise, clicks, and frequency-modulated sounds were recorded with extracellular microelectrodes. A majority of the units responded to acoustic stimulation, pure tone pips being the most effective in terms of the percentage of units responding (71%). No simple catalogue of response types could be elicited. Units varied in terms of the combinations of stimuli to which they were responsive, the frequency range over which pure tones were effective, and the temporal pattern of discharge to different frequencies and different types of stimuli. A substantial majority of units gave precise timed responses to the onset or offset of the stimuli, while a few introduced long delays between the stimulus and the response. With regard to the area studied, acoustic units could be found between stereotaxic coordinates A3 and A10, both on the lateral surface of the hemisphere and in the superior temporal plane, as well as in the caudal insular region. No precise tonotopic organization could be discerned. [ABSTRACT FROM AUTHOR]