OSCILLATIONS IN LOCAL-FIELD POTENTIALS OF THE PRIMATE MOTOR CORTEX DURING VOLUNTARY MOVEMENT

We investigated the occurrence and distribution of oscillatory activit y in local field potentials (LFPs) recorded from the frontal motor cor tex of behaving monkeys performing skilled voluntary movements. LFPs w ere recorded simultaneously from up to 12 sites distributed throughout motor cortex while monkeys performed a visually guided, instructed de lay task using the wrist or digits. Oscillatory activity between 15 an d 50 Hz was evident in the LFP recorded from both primary motor cortex and premotor areas. Oscillations occurred preferentially before the v isual cue to initiate movement but were infrequent during movement. Os cillations typically stopped before movement initiation during the wri st task, although they often continued into the initial phases of move ment during the digit task. The relationship of oscillations to task p erformance was consistent across trials over periods of many months, a lthough the amplitude and duration of oscillations varied across trial s and days. Interactions between pairs of LFP recordings, evaluated wi th cross-correlation analysis, revealed synchronous oscillations over long distances (>7 mm) and across primary motor cortex and premotor re cording sites. These studies demonstrate that oscillations recorded in the LFP in motor cortex during trained motor tasks are not related to the details of movement execution but may be related to aspects of mo vement preparation.