Effect of low and high frequency thalamic stimulation on sleep in patientswith Parkinson's disease and essential tremor

Continuous high frequency stimulation of the ventral intermediate nucleus o f the thalamus (Vim), delivered through surgically implanted quadripolar el ectrodes, alleviates tremor in Parkinson's disease (PD) and essential tremo r (ET). The Vim is adjacent to the thalamic reticular nuclei, where sleep s pindles originate according to animal models. In order to determine whether Vim stimulation affects sleep spindles, six patients (4 PD, 2 ET), aged 60 -69 years, were recorded on a control night and a stimulation night (130 Hz , 2-3 V; right stimulation in five patients and bilateral stimulation in on e patient). Stimulation did not modify sleep quality or architecture. Sleep spindles were present and symmetrical in five out of six patients under st imulation. However, in one patient with a sustained 'thalamotomy-like effec t' that abolished tremor, spindles were asymmetrical even without stimulati on. In each patient, spindle density was similar on both nights (mean +/- S EM: 2.25 +/- 0.61 spindles per min of stage 2 sleep vs. 1.84 +/- 0.31). In an attempt to promote sleep two different patterns of stimulation were appl ied in the region of ventrooralis posterior and reticularis nuclei in five patients in the awake state. Continuous low frequency stimulation (5 Hz, 0. 1 V), and repeated trains of 15 Hz for 1 s every 15 s mimicking the pattern of physiological spindles, each failed to induce sleep or cortical synchro nization. We conclude that Vim stimulation, unlike thalamotomy, selectively reduces tremor without altering sleep or sleep spindles. Our results also suggest that low frequency stimulation applied in the region of the reticul ar nuclei does not induce sleep.