NEUROMAGNETIC STUDY OF MOVEMENT-RELATED CHANGES IN RHYTHMIC BRAIN ACTIVITY

Neuromagnetic fields from the left cerebral hemisphere of five healthy , right-handed subjects were investigated in a typical Bereitschaftspo tential paradigm consisting of self-paced voluntary movement of the ri ght index finger, To assess movement-related spectral changes of the s pontaneous magnetoencephalogram, latency- dependent short-time spectra were obtained by Fourier analysis for each single trial, The number o f trials in which the spectral estimate for a certain frequency and la tency deviated from reference values was then transformed into a proba bilistic relative power measure, A spectral power depression around 20 Hz was observed starting about 2.5 s before movement onset, followed by elevated power in the 20-35 Hz range starting about 500 ms after mo vement onset. Generally, the power increase differed from the prior de pression in both spectrum and topography, suggesting different generat ing processes rather than just a 'rebound' effect of the idling rhythm generator. The time course and topography of spectral power changes a re discussed in relation to the corresponding properties of the moveme nt-related neuromagnetic fields (readiness field, motor field, and mov ement-evoked field I).