The auditory steady-state response (ASSR) elicited by a periodic sound stimulus is a neural oscillation recorded by magnetoencephalography (MEG), which is phase-locked to the repeated sound stimuli. This ASSR phase alternates after an abrupt change in the feature of a periodic sound stimulus and returns to its steady-state value. An abrupt change also elicits a MEG component peaking at approximately 100-180 ms (called "Change-N1m"). We investigated whether both the ASSR phase deviation and Change-N1m were affected by the magnitude of change in sound pressure. The ASSR and Change-N1m to 40 Hz click-trains (1000 ms duration, 70 dB), with and without an abrupt change (± 5, ± 10, or ± 15 dB) were recorded in ten healthy subjects. We used the source strength waveforms obtained by a two-dipole model for measurement of the ASSR phase deviation and Change-N1m values (peak amplitude and latency). As the magnitude of change increased, Change-N1m increased in amplitude and decreased in latency. Similarly, ASSR phase deviation depended on the magnitude of sound-pressure change. Thus, we suspect that both Change-N1m and the ASSR phase deviation reflect the sensitivity of the brain's neural change-detection system.
Keywords: ASSR; N1m; change detection; magnetic field; sound pressure.