Magnetoencephalography and stereopsis: rhythmic cortical activity in humans recorded over the parieto-occipital cortex

We have studied human stereopsis by analysing magnetoencephalographic signa ls during the presentation of stereograms using frequency analysis. The stu dy of synchronised firing of cortical neurones is a new way of understandin g information processing in the brain and it is hypothesised that frequenci es greater than 35 Hz are used for higher-order processing. We report the r esponse of cortical neurones involved in stereopsis recorded from over the occipital and parietal cortices using a single channel axial superconductin g quantum interference device neuromagnetometer. Our main result was increa sed cortical activity in the gamma-band at frequencies apparently related t o stereopsis and the perception of depth. Our results are consistent with r eports in the literature that suggest that frequencies above 40 Hz are invo lved in attention, pattern recognition and higher order visual activity. (C ) 2001 Elsevier Science Ltd. All rights reserved.