Neuroscience Letters 367 (2004) 6–9 Gamma band responses to target and non-target auditory stimuli in humans

We studied the EEG oscillatory changes in the gamma band during auditory oddball paradigms in two different conditions (counting targets and reading). A time–frequency analysis was performed for standard and target stimuli. The study revealed an early (26–59 ms) phase-locked oscillation. Around 200 ms, a non-phase locked response was found for standard and target stimuli in temporal posterior electrodes. At about 360 ms, a phase-locked oscillation was observed only after target stimuli in the “counting targets ” condition. During the “reading ” task this late activity was not found, and energy increases were lower than during “counting ” task. The early oscillation may be related to the sensory processing of the stimuli. The response around 200 ms may be involved in auditory mismatch and/or memory retrieval, and late activity is probably a P300-related response. Attention enhances all these activities