OBJECTIVES: We investigated the effects of deep brain stimulation (DBS) or 
lesions of the ventral intermediate nucleus (Vim) of the thalamus for 
spinocerebellar ataxia (SCA) and examined the pathophysiological role of 
neuronal activity of the Vim underlying ataxia.
METHODS: Five patients with SCA with cortical atrophy (ages 60-69 years; 2 
sporadic and three familial SCA) and five patients with essential tremor (ET) 
(ages 57-71 years) were treated with Vim surgery. Intraoperatively, we recorded 
neuronal activity from single neurons in the Vim thalamus while patients were at 
rest and compared the physiological properties of those neurons between patients 
with SCA and those with ET.
RESULTS: Postsurgery mean scores for the Fahn-Tolosa-Marin Tremor Scale were 
improved from 78 to 44 in SCA patients and from 54 to 21 in ET patients. 
Stronger stimulation was necessary to optimize outcomes in SCA as compared to ET 
patients. We analyzed 68 Vim neurons in SCA and 60 Vim neurons in ET. Mean 
discharge rates, burst characteristics, and oscillatory activity were similar 
for both patient groups, however, we observed that the ratio of cells responding 
to passive manipulation was significantly smaller (P = 0.0001) in SCA (22%) than 
in ET (71%).
INTERPRETATION: Thalamic surgery led to a significant improvement in tremor in 
SCA patients. One potential mechanism underlying ataxia in SCA may be disruption 
of cerebellar sensory feedback, which modulates motor commands in the 
cerebello-thalamo-cortical network.