Neuronal mechanisms of motor signal transmission in the thalamic ventrooral nucleus in spasmodic torticollis patients

A microelectrode technique was used to study the neuronal mechanisms of motor signal transmission in the ventrooral internus nucleus (Voi) of the motor thalamus during voluntary and involuntary pathological (dystonic) movements in patients with spasmodic torticollis. Voi cell elements proved highly reactive to various functional (mostly motor) tests. An activity analysis of 55 Voi neurons detected during nine stereotactic operations revealed, first, a difference in neuronal mechanisms of motor signal transmission for voluntary movements that do or do not involve the affected axial muscles of the neck and for passive and abnormal involuntary dystonic movements. Second, a sensory component was found to play a key role in the mechanisms of sensorimotor interactions during voluntary and involuntary dystonic head and neck movements activating the axial muscles of the neck. Third, rhythmic and synchronized activity of Voi neurons was shown to play an important role in motor signal transmission during voluntary and passive movements. The Voi nucleus was directly implicated in the mechanisms of involuntary head movements and tension of the neck muscles in spasmodic torticollis. The results can be used to identify the Voi nucleus of the thalamus during stereotactic neurosurgery in order to select the optimal destruction or stimulation target and to reduce the postoperative effects in spasmodic torticollis patients.