Role of the primary auditory cortex in auditory selective attention studied by whole-head neuromagnetometer

In order to identify the human cortical areas involved in the auditory attention, neuromagnetic fields were recorded from 12 healthy adults with a 122-channel whole-head magnetometer while the subjects performed the auditory selective attention task. Randomized sequence of 900 Hz (P=0.9) and 950 Hz (P=0.1) tones was presented to each ear with random interstimulus intervals across ears ranging from 300 to 500 ms. Subjects were asked to pay attention to the designated ear (attended ear) and to count the number of the 950 Hz tones presented to the attended ear. Twelve sessions were performed for each subject, among which the attended ear was changed alternately in a counterbalanced order among subjects. In seven out of twelve subjects, averaged neuromagnetic fields in response to frequent tones presented to the attended ear showed attention-related deflection over the bilateral temporal areas starting at around 100 ms after the stimulus presentation. Although the dipole moment for N100m in the attended condition showed significant increase compared to that in the non-attended condition, locations of the two equivalent current dipoles in the auditory cortex were not significantly different from each other. Moreover, a simulation study supported the enhancement of N100m rather than participation of additional dipoles in the auditory selective attention task. These results suggest that the primary auditory cortex plays a main role in the auditory selective attention starting as early as 100 ms after the stimulus presentation.