title: Subdural grid recordings of distributed neocortical networks involved with somatosensory discrimination.
abstract: Previous studies suggest that evidence for the sub-second activation of distributed neural networks can be obtained by computing the covariance between segments of the scalp-recorded evoked potential. However, the cortical representation of such potentials is not known. Here we report a case study where the evoked potential covariance (EPC) measure was applied to data recorded from a 58-channel subdural grid implanted in an epilepsy patient. Recordings were made while the patient performed a task that required judging the somatosensory intensities of electrical stimuli and executing precise finger flexion responses in response to a subset of those stimuli. Post-stimulus EPC patterns involved covariances between somatosensory, motor, and temporal regions. Pre-stimulus EPC patterns involved these same regions, but only when it could be anticipated that the upcoming stimulus would likely require a response. 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 conduction. Rather, they appeared to reflect the transient integration of activity across distinct cortical processing nodes.
authors.affiliation: EEG Systems Laboratory and Sam Technology, San Francisco, CA 94105.
authors.forename: A
authors.initials: A
authors.lastname: Gevins
authors.forename: B
authors.initials: B
authors.lastname: Cutillo
authors.forename: J
authors.initials: J
authors.lastname: Desmond
authors.forename: M
authors.initials: M
authors.lastname: Ward
authors.forename: S
authors.initials: S
authors.lastname: Bressler
authors.forename: N
authors.initials: N
authors.lastname: Barbero
authors.forename: K
authors.initials: K
authors.lastname: Laxer
mesh_terms: D000328:Adult; D001921:Brain / Q000503:physiopathology*; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000503:physiopathology; D004192:Discrimination, Psychological / Q000502:physiology*; D004558:Electric Stimulation; D004569:Electroencephalography; D004833:Epilepsy, Temporal Lobe / Q000503:physiopathology*; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D005260:Female; D006801:Humans; D011930:Reaction Time / Q000502:physiology