Evidence for distinct beta resonance frequencies in human EEG related to specific sensorimotor cortical areas

Objective: We studied event-related synchronization (ERS) of beta rhythms r elated to voluntary movement vs. stimulation of upper and lower limbs. The aim of this study was to investigate whether the frequency of the beta resp onse is related to specific regions within the sensorimotor strip. Methods: Self-paced movement and electrical stimulation of the dominant han d and foot/leg was investigated in 10 right-handed volunteers. The electroe ncephalogram was recorded from closely spaced electrodes over central areas and processed time-locked to movement-offset or stimulation. In order to i dentify the dominant frequency of the induced beta oscillations. time-frequ ency maps were calculated using the continuous wavelet transformation. For the specific beta frequency bands. the band power time courses were analyze d by quantifying the event-related (de-)synchronization (ERD/ERS). Results: Both limb movement and somatosensory stimulation induced bursts of beta oscillations appearing within I s after movement/ stimulation with a clear focus close to the corresponding sensorimotor representation area. Th e peak frequency was significantly lower over the hand area (below similar to 20 Hz) than at mid-central sites overlying the foot representation area (above similar to 20 Hz). But no difference was found between movement and stimulation of the respective limb. Conclusions: Analyzing the frequency of induced beta activity revealed conc omitant oscillations at slightly different frequencies over neighboring cor tical areas. These oscillations might be indicative for a resonance-like be havior of connected sub-networks in sensorimotor areas. (C) 2001 Elsevier S cience Ireland Ltd. All fights reserved.