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• Cognitive tasks (attention to task instructions, then task performance) can end afterdischarges caused by cortical stimulation. • Electrocorticographic coherence decreases progressively with these tasks, returning towards baseline when afterdischarges end. • These decreases may be due to emergent properties of the brain as a whole which might help modify seizures and other disorders. We previously studied efficacy of cognitive tasks on afterdischarge termination in patients undergoing cortical stimulation and found that diffuse wavelet cross-coherence changes on electrocorticography were associated with termination efficacy. We now report wavelet cross-coherence findings during different time segments of trials during which afterdischarges ended. For 12 patients with implanted subdural electrodes, we compared wavelet cross-coherence findings among several 1-second portions of cognitive tasks, reflecting task presentation, patient replies, and afterdischarge termination. Coherence decreased significantly and progressively over time for 16.89, 22.53, and 30.03 Hz frequency ranges, but increased with afterdischarge termination. Coherence first increased, and then decreased for the 7.13 Hz frequency range. The findings suggest that cumulative but non-specific factors, likely related primarily to attention, influence the coherence results throughout the task, with a separate effect due to resolution of the afterdischarges at the end. Task performance is well known to localize to specific brain regions and to be restricted in timing. In contrast, attention and overall mental activation might be due to emergent properties of brain as a whole and that are less circumscribed in space or time. Cognitive tasks might modify seizures and other neurological disorders. [ABSTRACT FROM AUTHOR]

• When cognitive effort ends afterdischarges, there are widespread changes in coherence. • These coherence changes are similar throughout the cortex, regardless of the distance between recorded sites. • This similarity suggests a pan-cortical effect that may complement the activity of regional and multiregional networks. 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. 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. We found that when afterdischarges were suppressed there were changes in electrocorticographic coherence that were similar throughout cortex, regardless of the distance between sites. The similarity implies coordination of the changes, and the similarity regardless of distance or location implies a pan-cortical effect. 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. [ABSTRACT FROM AUTHOR]

• Cognitive effort causes changes that are not limited to specific functional networks. • Cognitive effort can end afterdischarges in regions not functionally related to the cognitive task. • When afterdischarges end there are widespread coherence decreases within specific frequency ranges. Mental activation has been reported to modify the occurrence of epileptiform activity. We studied its effect on afterdischarges. In 15 patients with implanted electrodes we presented cognitive tasks when afterdischarges occurred. We developed a wavelet cross-coherence function to analyze the electrocorticography before and after the tasks and compared findings when cognitive tasks did or did not result in afterdischarge termination. Six patients returned for functional MRI (fMRI) testing, using similar tasks. Cognitive tasks often could terminate afterdischarges when direct abortive stimulation could not. Wavelet cross-coherence analysis showed that, when afterdischarges stopped, there was decreased coherence throughout the brain in the 7.13–22.53 Hz frequency ranges (p values 0.008–0.034). This occurred a) regardless of whether an area activated on fMRI and b) regardless of whether there were afterdischarges in the area. It is known that cognitive tasks can alter localized or network synchronization. Our results show that they can change activity throughout the brain. These changes in turn can terminate localized epileptiform activity. Cognitive tasks result in diffuse brain changes that can modify focal brain activity. Combined with a seizure detection device, cognitive activation might provide a non-invasive method of terminating or modifying seizures. [ABSTRACT FROM AUTHOR]

Abstract: Objective: To study when afterdischarges (ADs) are more likely to occur during cortical stimulation. Methods: We examined 6250 electrical stimulation trials in 13 patients with subdural electrodes, studying whether AD occurrence during a trial was influenced by electrode pair stimulated or AD occurrence during the previous trial. In total 545 electrodes were stimulated, 119 frontal (pre-perirolandic), 289 perirolandic, 36 parietal (post-perirolandic), 95 temporal, and 6 occipital. Results: When the same electrode pair was stimulated as the prior trial, 19% produced ADs compared to 5% of trials when a different electrodes pair was stimulated (p <0.0001). When trials showed ADs, and the next trial stimulated the same electrode pair, ADs occurred in 46% of cases, compared to 13% of trials following trials without ADs (p <0.0001). AD probability decreased with increased inter-trial interval length only when the prior trial was at the same electrode pair and had produced an AD (p =0.001). AD probability increased with stimulation duration, whether the trial followed a trial with (p <0.001) or without (p <0.0001) an AD. Conclusions: ADs were more likely to occur when an electrode pair showed ADs and was stimulated again, especially when stimulating after short inter-trial intervals or for longer duration. Significance: When ADs occur, waiting about a minute before resuming stimulation might lessen the likelihood of AD recurrence. [Copyright &y& Elsevier]

Abstract: Subdural electrodes are frequently used to aid in the neurophysiological assessment of patients with intractable seizures. We review their use for localizing cortical regions supporting movement, sensation, and language. [Copyright &y& Elsevier]

Abstract: Subdural electrodes are frequently used to aid in the neurophysiological assessment of patients with intractable seizures. We review the indications for these, their uses for localizing epileptogenic regions and for localizing cortical regions supporting movement, sensation, and language. [ABSTRACT FROM AUTHOR]