Plasticity of spectrotemporal sensitivities in auditory cortex

Abstract

Response characteristics of auditory cortex can be altered by repeatedly pairing sounds with basal forebrain stimulation [M. P. Kilgard and M. M. Merzenich, Science 279, 1714–1718 (1998)]. Although many neurons in auditory cortex respond most strongly to time-varying sounds, most studies of stimulation-induced plasticity have focused on changes in responses to tone pips. We examined stimulation-induced changes in neuronal sensitivities to frequency-modulated sweep trains (bandwidth=2–16 kHz, duration=1 s, sweep rates=4–24 octaves/s, repetition rates=2–24 sweeps/s). Adult rats received electrical stimulation of basal forebrain paired with 1–10 varieties of sweep trains, 300–500 times per day, for 9–16 days. Some sounds were presented in combination with bandlimited Gaussian noise. After stimulation, neuronal responses were recorded from 20–80 sites in the auditory cortex of each rat. The spectrotemporal sensitivities of auditory cortical neurons were dramatically altered in stimulated rats. Changes in response characteristics were not straightforwardly related to features of the sounds that had been paired with stimulation. Certain sounds that normally evoked responses correlated with sweep repetition rate in control rats tended to evoke either aperiodic or uncorrelated periodic responses from neurons of stimulated rats. Current theories of auditory cortical plasticity do not account for these results. [Work supported by MBRS, NIMH, NSF.]