Timing of pure tone and noise-evoked responses in macaque auditory cortex.

We compared onset latencies for characteristic frequency pure tone and broadband noise responses in AI and posterior belt regions of the auditory cortex in awake macaques. We found that (1) in AI, responses to characteristic frequency tones and broadband noise have similar latencies, (2) in belt regions, characteristic frequency tone and broadband noise latencies differ significantly; broadband noise latencies are shorter, while characteristic frequency tone latencies are longer than corresponding values in AI, (3) for both pure tone and broadband noise responses in AI, latency decreases with increasing characteristic frequency and (4) despite a similar inverse relationship of tone latency and local characteristic frequency in belt areas, broadband noise latencies are uniformly short, and appear unrelated to local characteristic frequency. Dissociation of broadband noise and pure tone latencies may reflect the use of parallel anatomical routes into belt regions.