Independence of steady-state 40-Hz response and spontaneous 10-Hz activity in the human auditory cortex

We recorded neuromagnetic signals from 5 subjects with a 24-channel planar SQUID gradiometer. Our aim was to search for any relationship between the 40-Hz steady-state responses and the spontaneous 10-Hz activity in the auditory cortex. Source strengths and locations of spontaneous activity were determined from spectral components of the data, and sources within the auditory cortex were determined by restricting the source location to a neighborhood of the auditory evoked response to single clicks. The characteristics of the 40-Hz steady-state responses were not simply related to those of the spontaneous 10-Hz activity, even within subjects, suggesting that these two oscillatory phenomena have independent generators.