Characteristics of neurons in auditory cortex of monkeys performing a simple auditory task.

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Abstract
Response characteristics of 241 neurons from area A1 and the surrounding belt areas of auditory cortex were studied in unanesthetized monkeys that were performing a simple auditory reaction-time task. Estimates of best frequency, temporal response pattern, and other response characteristics were made on-line. Data from 154 of the units were recorded on magnetic tape for offline quantitative analysis. A clear tonotopic organization was seen in areas A1 and L, with high frequencies represented posteriorly and low frequencies, anteriorly. The organization was more complex than that seen in anesthetized monkey cortex; there were clear exceptions to a simple tonotopic organization. Of the cells studied 22% showed monotonic rate versus intensity functions, 53% showed simple nonmonotonic functions and 25% showed complex nonmonotonic functions. This representation of intensity information is distinctly different from that reported for inferior colliculus under similar circumstances. At the cortical level, the number of nonmonotonic intensity functions is significantly increased, suggesting that the cortex may be involved in processes requiring specific information about stimulus intensity. The most common response pattern was a single on-excitatory response. Response duration varied widely, but the majority of responses were of short duration (greater than 20 ms but less than 80 ms). The distribution of response patterns differed from that in anesthetized cat and differed slightly from that in awake but untrained monkeys. Response latencies for areas A1 and L average 26.5 ms, and no significant difference was seen between the 2 areas. A number of longer latency responses were recorded from area RL. Spontaneous rate did not differ appreciably from that seen in inferior colliculus under comparable conditions, but was lower than that seen at the periphery of the auditory pathway.