Inter- and intralimb oscillator coupling in parkinsonian tremor

This study reports the findings of an analysis of temporal correlation betw een tremor of different muscles of the same and different limbs in four pat ients with Parkinson's disease. Spectral coherence methods were used for de termining whether simultaneously occurring oscillations in the electromyogr ams of different muscles are statistically coupled. The incidence of signif icant coherence was considerably higher for muscle pairs in the same limb t han for pairs in different limbs; Parkinson's disease tremor is coupled wit hin but not between limbs. Because the characteristics of tremor are known to vary under different behavioral situations, the intralimb coupling was e xamined for different tasks. A mental arithmetic task resulted in an increa se in the coherence between muscles of the same limb, whereas the finger-to -nose task decreased the coherence. No significant change in coherence was found for a postural task. The amplitude and regularity of tremor electromy ography showed changes analogous to those in coherence. These results suppo rt the hypothesis that tremor in different limbs results from the activity of several neural circuits oscillating independently. The results also emph asize the value of these methods for rigorously characterizing tremor, in r elation to disease state, behavioral conditions, and the selection of treat ment strategies.