Human auditory cortex is activated by omission of auditory stimuli

Cortical signals associated with infrequent tone omissions were recorded from 9 healthy adults with a whole-head 122-channel neuromagnetometer. The stimulus sequence consisted of monaural (left or right) 50-ms 1-kHz tones repeated every 0.2 or 0.5 s, with 7% of the tones randomly omitted. Tones elicited typical responses in the supratemporal auditory cortices. Omissions evoked strong responses over temporal and frontal areas, independently of the side of stimulation, with peak amplitudes at 145-195 ms. Response amplitudes were 60% weaker when the subject was not attending to the stimuli. Omission responses originated in supratemporal auditory cortices bilaterally, indicating that auditory cortex plays an important role in the brain's modelling of temporal characteristics of the-auditory environment. Additional activity was observed in the posterolateral frontal cortex and in the superior temporal sulcus, more often in the right than in the left hemisphere.