Auditory on- and off-responses and alpha oscillations in the human EEG

In the present study, the wide band alpha and sub-bands of alpha in the auditory on- and off-responses to different stimulation frequencies were evaluated. Auditory on- and off-responses of 12 healthy volunteers (average 17 years old) were recorded from five locations (Fz, Cz, Pz, P3, and P4). The auditory stimuli of 80 dB SPL and 1000 ms duration were delivered at six different stimulation frequencies (f1-f6; 0.2, 0.6, 1, 2, 3, and 4 kHz, respectively). In using individual alpha frequency (IAF) as individual anchor point, wide band alpha and three different alpha frequency sub-bands with a bandwidth of 2 Hz each were defined: lower-1 alpha, lower-2 alpha, and upper alpha. The Root Mean Square (RMS) values of the alpha frequency bands were computed for two time periods: +/- 3 sd around the mean peak latency of the auditory on-responses (t1-on and t2-on) and a time window of the same length of the auditory off-responses (t1-off and t2-off). The alpha RMS values of both on- and off- responses showed significant differences between t1 and t2 periods on wide band, lower-1 and lower-2 alpha bands, especially at 0.2, 0.6, 1, 2, and 3 kHz stimulation frequencies in all recording places. Amplitudes in anterior locations (Fz, Cz) were higher than the others. These observations may provide a preliminary but nonetheless important understanding of how information may be processed in the brain.