Modulating Oscillations and Working Memory in Patients With Subdural Electrodes

The aim of this study is to characterize the entrainment of endogenous neural oscillatory activity using direct electrical stimulation (DES) of the brain and understand the effects on cognition. In this study, the investigators will apply rhythmic DES to patients who are undergoing routine DES for cortical mapping as a part of their epilepsy surgery evaluation with the aim of entraining cortical neural oscillations at specific frequencies relevant to cognitive processing and neuropsychiatric disease. The investigators hypothesize that rhythmic DES within a naturally occurring oscillatory frequency will cause entrainment at that frequency (e.g. 10Hz rhythmic DES will entrain a 10 Hz alpha oscillation). Also, the investigators posit that rhythmic DES at the theta (5Hz), alpha(10Hz), and gamma (50Hz) frequencies will cause enhancement of neural oscillations in the gamma band. The study follows a within-participant crossover design. Participants will perform one of the tasks described below and each task consists of multiple trials of varying difficulty. Stimulation will be applied concurrently through electrodes implanted for clinical determination of seizure focus. Equal number of stimulation and sham trials will be pseudo-randomly interleaved to get a balanced design (balanced across trial difficulty and trial type). The investigators will apply electrical stimulation in the form of pulse trains. The applied electrical stimulation intensity, duration and frequency follow the parameters used for clinical assessments of language and seizure focus and fall below the clinically approved limits. The investigators will measure participants performance on a simple working memory task during the above-described cortical electrical stimulation protocol. Alternately, participants can perform a face recognition task.