Spectrotemporal sensitivities in rat auditory cortical neurons

Studies in several mammalian species have demonstrated that auditory cortic al neurons respond strongly to single frequency-modulated (FM) sweeps, and that most responses are selective for sweep direction and/or rate. In the p resent study, we used extracellular recordings to examine how neurons in th e auditory cortices of anesthetized rats respond to continuous, periodic tr ains of FM sweeps (described previously by deCharms et al., Science 280 (19 98) pp. 1439-1444, as moving auditory gratings). Consistent with previous o bservations in owl monkeys, we found that the majority of cortical neurons responded selectively to trains of either up-sweeps or down-sweeps; selecti vity for down-sweeps was most common. Periodic responses were typically evo ked only by sweep trains with repetition rates less than 12 sweeps per seco nd. Directional differences in responses were dependent on repetition rate. Our results support the proposal that a combination of both spectral and t emporal acoustic features determines the responses of auditory cortical neu rons to sound, and add to the growing body of evidence indicating that the traditional view of the auditory cortex as a frequency analyzer is not suff icient to explain how the mammalian brain represents complex sounds. (C) 20 01 Published by Elsevier Science B.V.