Neural dynamics of ignoring and attending in human auditory cortex

2 Studies in all sensory modalities have demonstrated amplification of early brain responses to attended signals, but less is known about the processes by which listeners selectively ignore stimuli. Here we use MEG and a new paradigm to dissociate the effects of selectively attending, selectively ignoring and passively listening. Two different tasks were performed successively on the same acoustic stimuli: triplets of tones (A, B, C) with noise-bursts interspersed between the triplets. In the COMPARE task subjects were instructed to respond when tones A and C were of same frequency. In the PASSIVE task they were instructed to respond as fast as possible to noise-bursts. COMPARE requires attending to A and C and actively ignoring tone B, but PASSIVE involves neither attending nor ignoring. The data were analyzed separately for frontal and auditory-cortical channels, to independently address attentional effects on low-level sensory areas, control processes and preparatory states. The earliest (100 ms) attend/ignore effects in auditory cortex appear to be generated by modulation of exogenous (stimulus-driven) sensory evoked activity. Specifically as related to ignoring, we demonstrate that as in studies of selective attention, active-ignoring-induced input inhibition involves early selection. We identified a sequence of early (<200ms post onset) auditory cortical effects, comprised of onset response attenuation and the emergence of an inhibitory response and provide new direct evidence that listeners actively ignoring a sound can reduce their stimulus related activity in auditory cortex by 100 ms after onset when this is required to execute their behavioral objectives.