Parieto-temporal rhythms in the 6–9 Hz band recorded in epileptic patients with depth electrodes in a self-paced movement protocol

Objectives: Description of 6–9 Hz rhythmic electrical activity observed on recordings from electrodes implanted in the cortex of epileptic patients undergoing presurgical evaluation. Methods: Recordings were obtained from 74 patients with multilead electrodes in the frontal, parietal and temporal cortex. The motor task consisted of a self-paced fist clenching movement at approximately 10 s intervals. Events within a window extending from 4 s before to 1 s after movement EMG onset were analyzed. Results: (i) Spindle-like rhythmic activity at 6–9 Hz was observed in 29 patients. (ii) This activity was located in the inferior parietal and superior temporal areas. (iii) Enhancement of rhythmic activity occurred when patients were asked to perform the motor task. (iv) A striking tendency to phase-locking of rhythmic oscillations on consecutive trials was noted during the 3–2 s epoch before movement EMG onset. Conclusion: Whether this intracerebrally recorded 6–9 Hz rhythmic activity belongs to the mu–alpha class or is a special type of theta, and if it is related to the epileptic process or to drug treatment remain open to discussion. Motor-task related enhancement and phase-locking suggest that this activity may be one more indicator of movement preparation.