Scalp potentials follow the low frequency envelope of complex acoustic stimuli

Scalp potentials which follow the low frequency envelope of an amplitude modulated (AM) stimulus waveform were evoked and recorded from anesthetized gerbils. This envelope following response is presumably due to the synchronized discharge of populations of neurons in the auditory pathway. AM stimuli, alone and in the presence of pure-tone maskers of varying frequencies, were presented and scalp potentials recorded. A strong envelope following response, at the frequency of the modulator, was obtained to AM stimuli alone. The response could be eliminated by the simultaneous presentation of a masking stimulus (f_mask ). When f_mask was close to the carrier frequency, responses at the modulation frequency were diminished by up to 20 dB. Measurements of the group delay, determined from the phase of the response relative to the stimulus phase, indicate that the response is generated in at least three distinct brain regions