Time courses of cortical beta and gamma‐band activity during listening to metronome sounds in different tempi.

Oscillatory cortical activities in beta-band (13–20 Hz) are related to a somatomotor system, and gamma-bands (20 Hz) are involved with feature binding in perception. Previously gamma-band activity in electroencephalography was found to modulate with musical pulse with a two-beat metric accent. The present study examined beta- and gamma-band activities in auditory cortices recorded via magnetoencephalography (MEG) when subjects listened to musical pulse in various tempi. Tones were presented with intervals of (1) 390 ms, (2) 585 ms, and (3) 780 ms, and (4) with irregular intervals between 390 and 780 ms. In addition, the same tones were presented with a 390-ms interval using a two-beat accent, while occasionally either (5) an accented tone or (6) an unaccented tone was omitted. Beta-band activity decreased immediately after the stimulus and returned to the previous level just before the next stimulus, regardless of the tempo, except in the irregular condition. The tone omission resulted in an extra beta rebound. Gamma-band activity increased right after the pulse or the omission. We propose that beta oscillations may encode the timing of the next sound in a regular pulse sequence, whereas gamma oscillations likely reflect processing of the current auditory events including omissions.