The Journal of Neurophysiology Vol. 82 No. 3 September 1999, pp. 1542-1559
Copyright ©1999 by the American Physiological Society
Leibniz-Institut für Neurobiologie, 39118 Magdeburg, Germany
Brosch, Michael,
Andreas Schulz, and
Henning Scheich.
Processing of Sound Sequences in Macaque Auditory Cortex:
Response Enhancement. J. Neurophysiol. 82: 1542-1559, 1999. It is well established that the tone-evoked
response of neurons in auditory cortex can be attenuated if another
tone is presented several hundred milliseconds before. The present
study explores in detail a complementary phenomenon in which the
tone-evoked response is enhanced by a preceding tone. Action potentials
from multiunit groups and single units were recorded from primary and caudomedial auditory cortical fields in lightly anesthetized macaque monkeys. Stimuli were two suprathreshold tones of 100-ms duration, presented in succession. The frequency of the first tone and the stimulus onset asynchrony (SOA) between the two tones were varied systematically, whereas the second tone was fixed. Compared with presenting the second tone in isolation, the response to the second tone was enhanced significantly when it was preceded by the first tone.
This was observed in 87 of 130 multiunit groups and in 29 of 69 single
units with no obvious difference between different auditory fields.
Response enhancement occurred for a wide range of SOA (110-329 ms) and
for a wide range of frequencies of the first tone. Most of the first
tones that enhanced the response to the second tone evoked responses
themselves. The stimulus, which on average produced maximal
enhancement, was a pair with a SOA of 120 ms and with a frequency
separation of about one octave. The frequency/SOA combinations that
induced response enhancement were mostly different from the ones that
induced response attenuation. Results suggest that response
enhancement, in addition to response attenuation, provides a basic
neural mechanism involved in the cortical processing of the temporal
structure of sounds.