Attentional modulation of cortical neuromagnetic gamma response to biological movement.

Processing of biological motion represented solely by a set of lights on the joints of a human body is traditionally viewed as largely independent of attention. Here, by manipulating attention-related task demands, we assess changes in the neuromagnetic cortical response to a point-light walker. Irrespective of task demands, biological motion evokes an increase in oscillatory gamma activity over the left parieto-occipital region at 80 ms post-stimulus. Only an attended walker, however, yielded further peaks over the right parietal (120 ms) and temporal (155 ms) cortices. By contrast, the magnetoencephalographic (MEG) response to an ignored walker is restricted to the left parieto-occipital region. In addition, peaks in oscillatory activity occur in response to both attended (canonical and scrambled) configurations at 180-200 ms from stimulus onset over the right fronto-temporal regions, most likely reflecting maintenance of the target configuration in working memory. For the first time, we demonstrate that the time course and topographic dynamics of oscillatory gamma activity in response to biological movement undergoes top-down influences and can be profoundly modulated by the withdrawal of attention.