Importance of microstereoencephalotomy for tremor alleviation

Application of the microelectrode technique in human stereotactic surgery, which is especially important for tremor control, is now routine for the procedure in our surgical theater. Neurons responsible for tremor generation can very delicately and exactly be identified within the ventralis intermedius nucleus (Vim) of the thalamus, which automatically determines the location of the minimum required thermocoagulation lesion to abolish tremor. Neurons with rhythmic burst discharges, which are synchronus in phase to the peripheral tremor, are organized in delicate somatotopic fashion within the Vim. Electrical stimulation of the neuron area through this microelectrode usually inhibits tremor of the corresponding area and a small thermocoagulation lesion, usually 3 mm in diameter, permanently abolishes tremor. These three findings, i.e., existence of rhythmic bursts, effect of the stimulation and surgical lesion, are the same in parkinsonian tremor, postural tremor and intention tremor. Physiological interpretation of different types of tremor will be proposed. In the cases of idiopathic neck tremor, a single Vim neuron corresponded to four neck muscles, i.e., bilateral sternocleidomastoid muscle (SCM) and bilateral posterior neck muscles, and most markedly to the controlateral posterior neck muscle and the ipsilateral SCM. Instrumentation of microstereoencephalotomy is also explained.