Modulation of the 40-Hz auditory steady-state response by attention during acoustic training

We investigated whether attention modulates the 40-Hz auditory steady-state response (SSR) which localizes to cortical sources in the region of primary auditory cortex (A1). Subjects in Group E performed a tone discrimination task requiring sustained attention. This task was preceded and followed by a passive stage in which identical stimuli were presented while subjects viewed a silent video. Control groups received three successive passive stages only (with or without the video). SSR amplitude increased from the passive baseline in Group E and with respect to both control groups when the discrimination task was performed, and reverted to baseline afterwards. The SSR source waveform was enhanced in the right hemisphere, implying modulation of A1 by attention in this hemisphere. SSR phase and 3d source parameters did not shift when the discrimination task was introduced, implying similar SSR A1 generators in the passive and task conditions. Enhancement of N1, P2, and N2 during the discrimination task pointed to concurrent modulation of secondary auditory cortex by attention.