Yasuhiro Kawashima

Microrecording for the Study of Thalamic Organization, for Tumor Biopsy and Removal

Use of microrecording technique in stereotactic selective thalamotomy, and in stereotactic biopsy for deep-seated lesions and in tumor removal was briefly described. For selective thalamotomy, the microrecording gives ample information to delineate thalamic subnuclei. Thus, the ventrointermedius (Vim) nucleus is identified by high-amplitude background activity and large-spike discharge, some of which responds solely to contralateral natural stimuli of kinesthetic modality. A small coagulation including this thalamic Vim point resulted in permanent arrest of the various kinds of tremor. As the normal brain tissue, whether the gray or white matter, is electrically active, the microrecording is useful to delineate the brain tumor from its surroundings. Stereotactic diagnostic biopsy and removal of the brain tumor were facilitated by this adjuvant method.

A special role of the parvocellular red nucleus in lesion-induced spontaneous tremor in monkeys.

The neural mechanisms underlying spontaneous tremor were investigated in monkeys. Tremor-producing ventromedial tegmental (VMT) lesions involve at least three major neural elements. (1) Parvocellular division of the red nucleus (RNpc); (2) cerebellothalamic fibers passing through the red nucleus, and, (3) nigrostriatal fibers. These three elements were destroyed stereotaxically in areas remote from the VMT area separately and/or in various combinations, and correlation between the site of lesions and tremor was made. Lesion-induced tremor appeared only when the three elements were destroyed. A possible, particular role of the RNpc in the production of the spontaneous tremor is discussed.

Tremor-Mediating Thalamic Zone Studied in Humans and in Monkeys

The thalamic zone mediating the rhythmic burst activity related to the contralateral tremor was studied by microelectrodes in clinical cases with tremor and in monkeys with experimental tremor. The rhythmic burst time-locked with the tremor was found in a restricted area of the ventrointermedius nucleus (Vim) in humans and also in VPLo nucleus in monkeys. In both cases, only the lateral and ventrocaudal part of each nucleus, which was defined as the kinesthetic zone, was involved. A possible tremor-mediating neural circuit is postulated.

The Possible Role of the Cerebral Cortex Adjacent to the Central Sulcus for the Genesis of Central (Thalamic) Pain—a Metabolic Study

In nine patients with central (thalamic) pain after stroke, X-CT, MRI, PET scan and intraoperative thalamic microrecordings were performed. The PET studies made use of Sokoloffs method with 18FDG and a steady-state method with C15O2-15O2. CT scan and MRI revealed definite thalamic damage (Th) in 3 cases, putaminal damage (Put) in 3 cases, combined damage (Th + Put) in one case, and cortical (parietal) damage in 2 cases. In patients with a subcortical lesion, the greater the severity of superficial pain, the higher was the relative value of regional cerebral glucose metabolism (rCMRGlu) as compared to oxygen metabolism (rCMRO2) in the cerebral cortex around the central sulcus on the damaged side. Also, in a case with combined (Th + Put) lesion, regional oxygen extraction ratio (rOEF) was increased in this area. Moreover, in another case, central pain disappeared after a small subcortical haemorrhage in the same structure. In all patients including those with a cortical lesion, rCMRGlu was decreased in the postero-lateral (sensory) thalamus on the invalued side. The possible role of the cerebral cortex around the central sulcus for the genesis of central pain is discussed.

Application of magnetic resonance imaging in functional stereotactic thalamotomy for the evaluation of individual variations of the thalamus.

An application of MRI in functional stereotactic thalamotomy is presented. To estimate the individual anatomic variations of the thalamus prior to stereotactic thalamotomy, a special study using a proton density image that shows myeloarchitectonic features of the thalamus was performed. The proton density MRI was demonstrated to be very useful to determine the safest trajectory and tentative target point. However, as a detailed functional localization of the thalamic subnuclei cannot be yet obtained by MRI, the final target should be decided on the basis of electrophysiological findings.

Strategy of Selective VIM Thalamotomy Guided by Microrecording

Our routine procedure for stereotactic selective Vim thalamotomy is described briefly. Preoperative steps identify the tremor qualitatively and quantitatively. The highlight of the procedure is the use of intraoperative microrecording to determine tremor time-locked rhythmic discharge in the presumed Vim nucleus. Results of the operation are also estimated quantitatively.

Stereotactic Vim-Vo-Thalamotomy for Choreatic Movement Disorder

Two cases with hemichorea and dopa induced dyskinesia (DID) were successfully treated with Vim-Vo thalamotomy. The findings of MRI and PET of these cases were variable because of the difference of their underlying disease processes. In the patients with hemichorea, high electrical activities with irregular bursts of discharge were recorded in Vo and Vim. These may be related to dysfunction of Vo underlying choreatic movement. Regardless of the causes, their choreatic movement was abolished by Vim-Vo thalamotomy affecting mainly Vo after physiological identification of Vim.

Pathophysiology of Central (Thalamic) Pain: A Possible Role of the Intralaminar Nuclei in Superficial Pain

In 15 patients with central pain (thalamic pain) after stroke, CT, PET scan and intraoperative thalamic microrecordings were performed. The results are considered together to evaluate a possible role of thalamic intralaminar nuclei in the genesis of central pain, especially of superficial pain. In the non-thalamic lesion group (deep pain dominant), thalamic background neural activity (BNA) was relatively high in Vim but low in CL. Conversely, in the thalamic lesion group (superficial pain dominant), thalamic BNA was higher in CL than in Vim, and markedly decreased in VC. In this group, regional cerebral oxygen consumption (rCMRO2) was relatively maintained, and regional oxygen extraction ratio (raOEF) and the relative value of regional cerebral glucose utilization (CMRGL), compared to rCMRO2, was increased in the cerebral cortex around the central sulcus. The genesis of superficial pain is discussed.

Plastic Change of Thalamic Organization in Patients with Tremor after Stroke

Thirteen patients with tremor after stroke were treated by stereotactic thalamotomy. Prior to making therapeutic lesions, microrecordings were tried and the findings were compared with our own results obtained in Parkinsons disease. Several characteristic features were revealed in terms of changes in electrical activity in and around the thalamic Vim nucleus. These findings support the idea that reorganization of the thalamic sensory nuclei might take place.

Stereotactic CT scan applied to stereotactic thalamotomy and biopsy

SummaryA Stereotactic method to visualize deep subcortical structures through which the electrode would pass intraoperatively is described in detail. The procedures are:1)Approximation of the tentative target point in the lateral craniogram according to some craniometric data.2)Determination of the invading route and its transfer to the patients scalp.3)CT scanning by a new generation scanner to distinguish between gray and white matter along the predetermined plane.4)Intraoperative adjustment of the electrode to the predetermined CT image and error correction.5)Verification by recording electrical activities in subcortical tissue. This simple method would be of great benefit for the accurate and safe performance of Stereotactic thalamotomy and biopsy.