Pan-cortical coordination underlying mental effort

Objective: It is well known that activity in, or coordination among, brain regions, can underlie movement, sensation, language, and cognition but there are observations that tasks unrelated to specific brain regions can nonetheless alter activity in those regions. These tasks might invoke activity in multiregional networks, but it also is possible that they are associated with changes beyond these networks. We therefore evaluated the possibility that more widespread, or even whole-cortical, mechanisms might complement or alter focal or multifocal cortical activity. Methods: We assessed the extent of electroencephalographic changes occurring outside areas with epileptiform activity, but that were associated with termination of the epileptiform activity. To do this, we measured the distribution of wavelet cross-coherence changes based on electrocorticography from 15 patients who showed regional afterdischarges in response to electrical brain stimulation prior to epilepsy surgery and in whom cognitive tasks were used in attempts to end the afterdischarges. There were 1276 electrodes implanted in these patients, and we analyzed a total of 55,494 electrode combinations. We compared recordings when cognitive effort was versus when it was not successful in ending afterdischarges. Results: We found that when afterdischarges were suppressed there were changes in electrocorticographic coherence that were similar throughout cortex, regardless of the distance between sites. Conclusions: The similarity implies coordination of the changes, and the similarity regardless of distance or location implies a pan-cortical effect. Significance: Our results provide physical support for hypotheses that pan-cortical processes complement the well-known regional and multiregional networks. These processes may participate in, be recruited by, modify, or underlie the conative experiences of waking life.