Chen H, Hua SE, Smith MA, Lenz FA, and
Shadmehr R (2006) Effects of cerebellar thalamus disruption on adaptive control
of reaching. Cerebral Cortex, 16:1462-1473.
Abstract: Lesion or degeneration of the
cerebellum can profoundly impair adaptive control of reaching in humans.
Computational models have proposed that internal models that help control
movements form in the cerebellum and influence planned motor output through the
cerebello-thalamo-cortical pathway. However, lesion
studies of the cerebellar thalamus have not consistently found impairment in
reaching or adaptation of reaching. To elucidate the role of the cerebellar
thalamus in humans, we studied a group of essential tremor (ET) patients with
deep brain stimulation (DBS) electrodes placed in the cerebellar thalamus. The
stimulation can be turned on or off remotely, and is thought to reduce tremor
by blocking the spread of the pathological output from the cerebellum. We
studied the effect of thalamic DBS on the ability to adapt arm movements to
novel force fields. While thalamic DBS resulted in a dramatic and significant
reduction of tremor in ET, it also impaired motor adaptation: the larger the
stimulation voltage, the greater the reduction in rates of adaptation. We next
examined ET patients that had undergone unilateral thalamotomy
in the cerebellar thalamus and found that adaptation with the contralateral arm
was impaired compared to the ipsilateral arm. Therefore, while both lesion and
electrical stimulation of the cerebellar thalamus are highly effective in
reducing tremor, they significantly impair the ability of the brain to form
internal models of action. Adaptive control of reaching appears to depend on
the integrity of the cerebello-thalamo-cortical
pathway
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