Units in the primary auditory cortex of the Japanese monkey can demonstrate a conversion of temporal and place pitch in the central auditory system

The present study has examined whether the temporal pitch known as the "missing fundamental" is co-place-coded with the place pitch in the auditory cortex, using adult Japanese monkeys (Macaca fuscata) prepared for chronic recordings. The stimuli were white noise bursts, tone bursts and bursts of a combination of higher harmonics of a low frequency. Unit recordings were made from the contralateral (left) primary auditory cortex (AI). During recording sessions, the animal was anesthetized with a mixture of nitrous oxide and oxygen, supplemented by ketamine and xylazine injections. The data have confirmed a tonotopicity, low frequency anteriorly while high frequency posteriorly, in A1 when the recording time window was short (c 20 msec) with stimulus a t threshold levels. For longer time windows andlor suprathreshold stimulus levels, determining the best frequency (BF) for a neuron was often difficult. In the low frequency area (I 500 Hz), the same neuron responded to BF as well as a combination of successive higher harmonics of BF without BF. However, they did not or little responded to the harmonics themselves. The findings imply that the temporally-coded pitch a t the periphery appears to be already place-coded together with the place pitch by the same neuron a t AI. This evidence agrees well with previous psychoacoustical findings.