SUBDURAL GRID RECORDINGS OF DISTRIBUTED NEOCORTICAL NETWORKS INVOLVEDWITH SOMATOSENSORY DISCRIMINATION

Previous studies suggest that evidence for the sub-second activation o f distributed neural networks can be obtained by computing the covaria nce between segments of the scalp-recorded evoked potential. However, the cortical representation of such potentials is not known. Here we r eport a case study where the evoked potential covariance (EPC) measure was applied to data recorded from a 58-channel subdural grid implante d in an epilepsy patient. Recordings were made while the patient perfo rmed a task that required judging the somatosensory intensities of ele ctrical stimuli and executing precise finger flexion responses in resp onse to a subset of those stimuli. Post-stimulus EPC patterns involved covariances between somatosensory, motor, and temporal regions. Pre-s timulus EPC patterns involved these same regions, but only when it cou ld be anticipated that the upcoming stimulus would likely require a re sponse. The majority of the observed EPCs occurred with non-zero time- lags, and these EPCs often involved non-adjacent electrode pairs. Thus , the observed EPCs were unlikely to arise solely from volume conducti on. Rather, they appeared to reflect the transient integration of acti vity across distinct cortical processing nodes.