Abstracts

Rationale: Cognitive activation can play a role in shifting brain states, but little is known about its effects on pathological brain dynamics in epilepsy. During the evaluation of patients implanted with subdural electrodes, electrical stimulation is often performed to localize motor, sensory, language, and other functional areas. Unfortunately, this stimulation can also precipitate after discharges (AD): electrical patterns that closely resemble epileptic seizures. We noted that, in some cases, AD could be suppressed by cognitive tasks such as answering a simple math question. We therefore asked how cognitive effort might alter the functional organization of the brain, and specifically whether the brain’s state prior to the question predicted success in stopping AD.Methods: Electrocorticographic (ECoG) recordings were obtained from patients who had subdural electrodes implanted for localization purposes as a part of efforts to treat their medically intractable epilepsy with surgical resections. During this evaluation, electrical stimulation was performed, producing AD in a subset of electrodes. Brain states were quantified using measures of functional network structure derived from ECoG recordings after AD began. The initial brain state was determined from a 4 s window while ADs were present, but before math questions were asked, and the resulting brain state was calculated from a 4 s window after the question was asked and before AD terminated. Data was sorted into cases where the cognitive effort was either successful or unsuccessful in stopping the AD, and changes in functional brain states were compared across the two conditions.Results: We observe that answering the math question induces frequency-dependent changes in the functional brain states that vary depending on whether or not AD terminated, and are most prevalent in the high gamma range (70-110 Hz). Additionally, we observe that cognitive effort is more likely to terminate the AD if the community structure present in the initial brain state is such that a large percentage of channels expressing AD are contained within a single network community.Conclusions: Our findings reveal that cognitive effort can impact functional brain states, and that the success of therapeutic interventions to mitigate epileptiform activity might be affected by an individual’s brain state at the time of the intervention.