Tremor-correlated cortical activity in essential tremor

Background In patients with parkinsonian resting tremor, tremor-correlated activity in the contralateral sensorimotor cortex has been studied by both magnetoencephalography (MEG) and electroencephalography (EEG). In essential tremor, MEG failed to detect cortical involvement. The objective of this s tudy was to investigate whether EEG recording can reveal tremor-correlated cortical activity in patients with essential tremor or enhanced physiologic al tremor. (MEG) tremor. Methods Seven patients with essential tremor and three patients with enhanc ed physiological tremor participated in the study. Unilateral postural trem or was activated by wrist extension on the right or on the left side. Elect romyography (EMG) signals arising from the wrist extensor and flexor muscle s, and a high-resolution EEG were recorded simultaneously. Coherences betwe en the time series of the rectified tremor EMG and the EEG were estimated. Findings In five of nine arms with essential tremor, we found highly signif icant coherences at the tremor frequency between the tremor EMG and the EEG . Isocoherence maps illustrating the topography of significant coherences o ver the scalp showed that the maximum coherences were located over the cont ralateral sensorimotor cortex. In the patients with enhanced physiological tremor, we were unable to detect consistent significant corticomuscular coh erences at the tremor frequency. Interpretation Using simultaneous EEG-EMG recordings, we showed that signif icant corticomuscular coherences at the tremor frequency can be found in es sential tremor. This finding contrasts with a recent study based on MEG rec ordings. The results suggest that the sensorimotor cortex is involved in th e generation of essential tremor. in a similar way to that previously shown in parkinsonian resting tremor.