Distinction of different fingers by the frequency of stimulus induced beta oscillations in the human EEG.

Induced beta oscillations were studied in three normal subjects after mechanical stimulation of each fingertip of the right hand. For stimulation short tactile stimuli of 10 ms duration were presented at intervals of 4 s. The electroencephalogram was recorded with 60 closely spaced electrodes and sampled at 256 Hz. For each subject the reactive beta band was determined by comparing 1-s power spectra. The largest beta power increase was found in the range of 12-28 Hz on electrodes overlying the left-hand area. The Matching Pursuit algorithm was applied to single trials data and the frequency of single "atoms" determined. In one subject the little finger showed a significant higher frequency as compared to the thumb. The difference in frequency was in the order of 1 Hz.

Early onset of post-movement beta electroencephalogram synchronization in the supplementary motor area during self-paced finger movement in man.

A voluntary finger movement is accompanied by an event-related desynchronization followed by a short burst of beta oscillations or event-related synchronization. These beta bursts are dominant over the contralateral hand representation area, but also appear over the midcentral area overlaying the supplementary motor area (SMA) and the foot representation area. We show that the induced midcentral beta oscillations following movement-offset display not only slightly higher frequency components, but have also a significantly earlier onset. These beta oscillations arise likely from the SMA. Assuming that the short-lasting beta synchronizations at frequencies below 35 Hz after termination of a movement reflect a state of localized cortical inhibition, we propose that the induced midcentral oscillations reflect the inhibition of networks within the SMA. This assumed resetting or inhibitory process within the SMA precedes that of the networks within the primary motor hand area.

Contrasting behavior of beta event-related synchronization and somatosensory evoked potential after median nerve stimulation during finger manipulation in man.

Electrical median nerve stimulation during rest results in two cortical responses: the somatosensory evoked potential (SEP); and the induced beta oscillations (beta event-related synchronization (ERS)). Both types of responses were recorded with electroencephalography and studied during rest and motor behavior in eight normal subjects. During manipulation of a cube with the fingers of the right hand, the beta ERS around 20 Hz, induced by right hand median nerve stimulation, is significantly suppressed, whereas the long-latency SEP components are significantly enhanced. The results suggest that both phenomena can be interpreted as responses of different neuronal structures in sensorimotor areas.