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The effect of diazepam on motor cortical oscillations and corticomuscular coherence studied in man
Ist Teil von
The Journal of physiology, 2003-02, Vol.546 (3), p.931-942
Ort / Verlag
Oxford, UK: The Physiological Society
Erscheinungsjahr
2003
Quelle
MEDLINE
Beschreibungen/Notizen
EEG recordings from sensorimotor cortex show oscillations around 10 and 20 Hz. These modulate with task performance, and are
strongest during periods of steady contraction. The 20 Hz oscillations are coherent with contralateral EMG. Computer modelling
suggests that oscillations arising within the cortex may be especially dependent on inhibitory systems. The benzodiazepine
diazepam enhances the size of GABA A IPSPs; its effects are reversed by the antagonist flumazenil. We tested the effect of these drugs on spectral measures of
EEG and EMG, whilst eight healthy human subjects performed a precision grip task containing both holding and movement phases.
Either an auxotonic or isometric load was used. EEG changes following electrical stimulation of the contralateral median nerve
were also assessed. The EEG power showed similar changes in all task/stimulation protocols used. Power around 20 Hz doubled
at the highest dose of diazepam used (5 mg), and returned to control levels following flumazenil. EEG power at 10 Hz was by
contrast little altered. The peak frequency of EEG power in both bands was not changed by diazepam. Corticomuscular coherence
at ca 20 Hz was reduced following diazepam injection, but the magnitude of this effect was small (mean coherence during steady
holding in the auxotonic task was 0.062 in control recordings, 0.051 after 2.5 mg and 5 mg doses of diazepam). These results
imply that 20 Hz oscillations in the sensorimotor cortex are at least partially produced by local cortical circuits reliant
on GABA A -mediated intracortical inhibition, whereas 10 Hz rhythms arise by a different mechanism. Rhythms generated during different
tasks, or following nerve stimulation, are likely to arise from similar mechanisms. By examining the formulae used to calculate
coherence, we show that if cortical oscillations are simply transmitted to the periphery, corticomuscular coherence should
increase in parallel with the ratio of EEG to EMG power. The relative constancy of coherence even when the amplitude of cortical
oscillations is perturbed suggests that corticomuscular coherence itself may have a functional role in motor control.