CENTRAL MECHANISMS IN HUMAN ENHANCED PHYSIOLOGICAL TREMOR

The sites of the central nervous structures involved in enhanced physi ological tremor (EPT) are still unclear. The syndrome of persistent mi rror movements (PMM) is characterized by abnormal bilateral corticospi nal projections. If a supraspinal mechanism is involved in EPT, the ac tivity of EPT should be coherent between both sides in subjects with t his abnormality. We investigated three PMM subjects and three normal c ontrols. Focal transcranial magnetic stimulation (TMS) resulted in con tralateral hand muscle responses in the controls. The PMM subjects, in contrast, had bilateral responses. Similarly, long-latency reflexes ( LLR) in PMM could be recorded bilaterally, while the control subjects showed responses only on the stimulated side. EPT was evoked by intrav enous salbutamol. EMG time series were recorded bilaterally from the w rist extensor muscles and cross spectra were calculated. If there was a significant right-left-coherence phase analysis was performed. No co ntrol subject showed a significant right-left-coherence of tremor acti vity. In contrast, a significant coherence was found in PMM between 8 and 12 Hz. When the mechanical tremor frequency of one hand was reduce d by loading, coherences and phase spectra of the EMGs remained unchan ged. By comparing the results from TMS, LLR and cross spectral analysi s we come to the conclusion, that the 8 to 12 Hz component of EPT is t ransmitted transcortically, most likely originating from two separate generators for both sides. (C) 1998 Elsevier Science Ireland Ltd.