This difference was significant between intention ET and postural ET groups (Kruskall–Wallis test H=2.84, P<0.05) but not between cerebellar

tremor and either essential tremor group (P>0.05). In combination with the analysis of coherence, these results demonstrate that postural ET is Inhibitor Library cost different from intention ET at the level of spike×EMG interaction. The results show that the physiology of postural ET is different from that of cerebellar tremor, as demonstrated in 7/9 physiological variables which were significantly different from cerebellar tremor. These 7 variables included: peak frequency in the tremor frequency range, firing rates (in Vim and Vop separately), incidence of sensory cells, firing rates of sensory cells, SNR, and SP600125 order coherence (in Vim only). Vop coherence, and phase lead were not different. Intention ET was not different from cerebellar tremor in any of these variables. Based on these results postural ET had more physiological differences from cerebellar tremor than intention ET had from cerebellar tremor (7/9 vs. 0/9, P<0.05, Fisher). These results suggest that postural ET is different from cerebellar tremor while intention ET is not. Postural ET had similar numbers of physiological differences from cerebellar

tremor and from intention ET (7/9 vs. 5/9, P=1, Fisher), which demonstrates again that intention ET is not apparently different from cerebellar tremor. We next examined the result of a cerebellar lesion in a patient with intention ET since the lesion should increase tremor due to a cerebellar disruption but decrease tremor due to a pacemaker in the cerebellum and related structures. Patient 4 (Table 1) with intention ET began to have tremor in the right upper extremity which then spread to the left. The patient had no family history of tremor and did not know the effect of alcohol upon the tremor. Propranolol and primidone have been tried without benefit. Tremor was demonstrated with posture and intention, both graded at 4/4 bilaterally on the Fahn clinical rating scale (Fahn et al., 1988). There

was no head tremor and the remainder of the neurological examination was within normal limits. The preoperative Tolmetin MRI scan was within normal limits. Fifteen years after the onset of tremor, the patient underwent an uncomplicated left thalamotomy which resulted in a small lesion, as shown in Fig. 1A (Lenz et al., 1994b). At follow-up 2 months later, the patient had a substantial improvement in activities of daily living, with a tremor rating of 1/4 in the right upper extremity with posture only. Twenty years after the onset of tremor, the patient had a total knee replacement and one week thereafter developed an acute onset of true vertigo and imbalance leading to falls, but no other symptoms or signs. These symptoms resolved and physical therapy was completed as planned.