Thalamic Ventralis Intermedius Research Articles

Response to Thalamic Ventralis Intermedius Nucleus Deep Brain Stimulation in Essential Tremor vs. Essential Tremor-Plus.

Introduction: Essential tremor (ET) is a tremor syndrome characterized by bilateral, upper limb action tremor. Essential tremor-plus (ET-plus) describes ET patients with additional neurologic signs. It is unknown whether there is a difference in response to treatment with ventralis intermedius nucleus deep brain stimulation (VIM DBS) in patients with ET and ET-plus. Due to potential variability in underlying etiology in ET-plus, there is a concern that ET-plus patients may have worse outcomes. The aim of this study was to identify whether patients with ET-plus have worse tremor outcomes after VIM DBS than patients with ET.Methods: This is a retrospective chart and video review evaluating VIM DBS outcomes by comparing changes from baseline in the Fahn-Tolosa-Marin Tremor Rating Scale Part B (FTM-B) for the treated limb between patients with ET and ET-plus at follow-up examinations. Patients were re-classified as having ET or ET-plus using pre-operative examination videos by two independent movement disorders neurologists blinded to patient characteristics. As a secondary outcome, we evaluated for correlations and potential predictors of treatment response.Results: Twenty-six patients were included: 13 with ET, 13 with ET-plus. There were no significant differences in the change in FTM-B scores between the ET and ET-plus patients at each follow-up examination. None of the included patients developed new symptoms compatible with dystonia, parkinsonism or gait disturbances.Conclusions: Patients with ET-plus had tremor improvement from VIM DBS, with no differences when compared to those with ET, without emergence of postoperative neurological issues. Patients with ET-plus should still be considered good candidates for VIM DBS for treatment of tremor.

Cognitive safety after unilateral magnetic resonance-guided focused ultrasound thalamotomy for essential tremor

Essential tremor (ET) is the most common movement disorder, affecting 1% of the population worldwide. There is sound evidence that medically refractory tremor improves with thalamotomy and deep brain stimulation...

Management of Elevated Therapeutic Impedances on Deep Brain Stimulation Leads.

Clinical VignetteA 64-year-old male with a history of essential tremor with bilateral thalamic ventralis intermedius deep brain stimulation implants had elevated therapeutic impedance values despite normal lead integrity impedances and good response to stimulation.Clinical DilemmaDo elevated therapeutic impedance values indicate a sign of hardware malfunction? What are the guidelines to approach deep brain stimulation hardware malfunction?Clinical SolutionLead integrity impedance values are a better evaluation of hardware integrity. The discrepancy between therapeutic and lead-integrity impedance values can arise when using low voltage settings.Gaps in KnowledgeThere are no established guidelines for the management of possible hardware malfunction in deep brain stimulation. The recommended approach is to distinguish between open and short circuit problems followed by an “inching” evaluation, assessing the structures from the implantable and programmable generator to the intracranial leads. Constant-current devices will deliver a more stable stimulation but the effect of their adoption is still not clear.Expert CommentaryThis case emphasizes the need for clinicians to understand fundamental differences in lead integrity and therapeutic impedance while utilizing a methodical approach in treating hardware malfunction. It highlights future avenues of investigation regarding the utility of constant current DBS technology.

Management of Elevated Therapeutic Impedances on Deep Brain Stimulation Leads

<strong>Clinical Vignette:</strong> A 64-year-old male with a history of essential tremor with bilateral thalamic ventralis intermedius deep brain stimulation implants had elevated therapeutic impedance values despite normal lead integrity impedances and good response to stimulation. <strong>Clinical Dilemma:</strong> Do elevated therapeutic impedance values indicate a sign of hardware malfunction? What are the guidelines to approach deep brain stimulation hardware malfunction? <strong>Clinical Solution:</strong> Lead integrity impedance values are a better evaluation of hardware integrity. The discrepancy between therapeutic and lead-integrity impedance values can arise when using low voltage settings. <strong>Gaps in Knowledge:</strong> There are no established guidelines for the management of possible hardware malfunction in deep brain stimulation. The recommended approach is to distinguish between open and short circuit problems followed by an ‘‘inching’’ evaluation, assessing the structures from the implantable and programmable generator to the intracranial leads. Constant-current devices will deliver a more stable stimulation but the effect of their adoption is still not clear. <strong>Expert Commentary:</strong> This case emphasizes the need for clinicians to understand fundamental differences in lead integrity and therapeutic impedance while utilizing a methodical approach in treating hardware malfunction. It highlights future avenues of investigation regarding the utility of constant current DBS technology.

The variability of atlas-based targets in relation to surrounding major fibre tracts in thalamic deep brain stimulation.

In essential tremor (ET), the main target for deep brain stimulation (DBS) is the thalamic ventralis intermedius nucleus (Vim). This target cannot be identified on conventional magnetic resonance imaging (MRI). Therefore, targeting depends on probabilistic coordinates derived from stereotactic atlases. The goal of our study was to investigate the variability of atlas-based Vim targets in relation to surrounding major fibre tracts. With the MRI and computed tomography (CT) scan data of ten patients who underwent DBS, we planned atlas based Vim targets in both hemispheres. We also performed deterministic fibre-tracking with diffusion tensor imaging (DTI) of the dentato-rubro-thalamic tract (DRTT), pyramidal tract (PT) and lemniscus medialis (LM) in all 20 hemispheres. Subsequently, we measured the distance from the atlas-based Vim target to each tract along the medial/lateral (x-coordinate), anterior/posterior (y-coordinate) and superior/inferior axis (z-coordinate). Seventeen out of 20 DRTTs could be depicted with our standardised DTI/fibre-tracking parameters. The PT and the LM could be displayed in all 20 hemispheres. The atlas-based Vim target was found inside the DRTT in 11 (concerning the x-coordinate) and 10 hemispheres (concerning the z-coordinate). Regarding the anterior/posterior direction, the target was posterior to the DRTT in 11 cases. In 19 hemispheres the Vim target was located medial and superior to the PT and in 17 hemispheres posterior to it. Concerning the LM, the Vim target was found inside the LM in 16 (regarding the x-coordinate) and in 14 cases (regarding the z-coordinate). In eight cases it was located inside and in 12 cases anterior to the LM concerning the y-coordinate. We found a considerable variability of the location of atlas-based target points of the ventralis intermedius nucleus in relation to neighbouring major fibre tracts in individual patients. These results suggest that individualised targeting to structures not directly visible on conventional MRI is necessary.

Parkinsonian thalamic electrical activities reveal voluntary versus involuntary movements in conflict

Objective: The aim of this study was to analyze the correlation between neuronal responses in the thalamic ventralis intermedius (Vim) nucleus to peripheral, natural stimulation and the modulation of tremor by electrical stimulation during stereotactic thalamotomy.Design and methods: The authors studied 36 patients with hand tremor using a microelectrode. The responses of tremor to electrical stimulation were analysed electromyographically. Sixty stimulation sites were divided into three groups.Results: Group A (20 sites) where responses to stretching of the contralateral forearm muscles were recorded. Group B (26 sites) where responses to stretching of the other muscles of the upper extremity were recorded. Electrical stimulation at sites in groups A and B temporarily suppressed the contralateral tremor, but the minimum current intensity to suppress tremor at sites in group A was less than that in group B. Electrical stimulation in group C (14 sites), where kinesthetic responses of contralateral lower extremity were recorded, resulted in increased amplitude of hand tremor. Selective coagulation including the area of tremor suppression resulted in abolition of the tremor in all patients.Conclusions: These results suggest that the most effective site for thalamotomy may also be suitable for chronic stimulation in the Vim nucleus.

Deep brain stimulation for treatment of hemichorea-hemiballism after craniopharyngioma resection: long-term follow-up

Hemichorea-hemiballism is a rare movement disorder that has various causes. In treatment-resistant cases, both thalamic and pallidal functional procedures have been shown to yield beneficial results. Until now it has not been clarified whether the thalamus or the pallidum would yield a superior outcome. After resection of a craniopharyngioma in this patient at the age of 49 years, hemichorea-hemiballism developed, with a latency of several weeks. Because the patient was greatly impaired by the movement disorder, she underwent implantation of deep brain stimulation (DBS) electrodes in the thalamic ventralis intermedius nucleus and the posteroventral lateral globus pallidus internus. Although both pallidal and thalamic stimulation could suppress the movement disorder, the voltage needed was clearly less with thalamic than with pallidal stimulation. At the last available follow-up 25 months postoperatively, complete subsidence of hemichorea-hemiballism was achieved with long-term thalamic stimulation. Long-term DBS therapy is an efficient treatment modality for refractory hemichorea-hemiballism in the long run (> 2 years). A bifocal (thalamic and pallidal) target paradigm allowed selection of the optimal stimulation site. Thalamic DBS was more favorable with regard to energy consumption.

Body weight gain and deep brain stimulation

Deep brain stimulation (DBS) is a neurosurgical technique that has now been available for some 25years. It is used in the treatment of various motor disorders, e.g. Parkinson's disease (PD), essential tremor and dystonia, and neuropsychiatric illnesses, e.g. obsessive–compulsive disorder and Tourette syndrome. The surgical targets of DBS include the thalamic ventralis intermedius nucleus (Vim), the globus pallidus internus (GPi) and more recently the subthalamic nucleus (STN), currently considered as the reference target in the treatment of PD. In the last ten years, most studies in PD patients have described a rapid and marked weight gain in the months following DBS of the STN. This weight gain sometimes induces obesity and can have metabolic repercussions. The physiopathological mechanisms responsible for the weight gain are multifactorial (changes in energy metabolism and eating behaviour, reduction of motor complications, etc.).This review reports current knowledge concerning weight changes in patients treated by DBS with different surgical targets. It also describes the mechanisms responsible for weight gain and the health outcome for the patients.

Ten Hertz thalamus stimulation increases tremor activity in the subthalamic nucleus in a patient with Parkinson’s disease

Objective In patients with Parkinson’s disease (PD) the effect of thalamic stimulation on tremor pathophysiology remains largely unclear. By recording local field potentials (LFPs) in the subthalamic nucleus (STN) while stimulating the nucleus ventralis intermedius thalami (VIM), information of the stimulation effects should be gained. Methods We had the unique opportunity to intraoperatively record LFPs of the STN in a patient with PD while stimulating the VIM. VIM electrodes had been implanted 9 years previously because of tremor. Due to worsening of clinical symptoms an implantation of STN electrodes had become necessary. Results High frequency stimulation in the VIM lowered the power of the tremor frequency band (4–7 Hz) in the STN. In contrast, 10 Hz VIM stimulation elevated the power of the tremor frequency band as well as STN–EMG coupling. Conclusions The effect of high frequency stimulation may explain the improvement of tremor in patients who are treated with VIM deep brain stimulation. The power elevation during 10 Hz stimulation suggests that the pathological cerebral and cerebral–muscular communication in PD is mainly driven at 10 Hz. Significance The direct cerebral recordings support the view that a 10 Hz network is a pathophysiological key mechanism in the generation of motor deficits in PD.

Quantification of Temporal and Spatial Accuracy of Alternating Arm Movements in Multiple Sclerosis Patients Treated with Deep Brain Stimulation of the Thalamic Ventralis Intermedius Nucleus (VIM)

In patients with multiple sclerosis (MS) ataxia is a common symptom, which is barely influenced by pharmacological treatment. We studied whether stimulation of the thalamic ventralis intermedius nucleus (VIM) improves the performance of alternating forearm movements in MS patients. We investigated 6 patients with primary (n=1) or secondary (n=5) chronic progressive MS (age 36-66 years, median 41.5 years, median EDSS [expanded disability status scale] 6.5). Patients were seated in a chair with one arm abduced at right angles to the body. This arm was strapped into a splint with one fixed section for the upper arm and one movable section for the forearm. The latter allowed horizontal movements in the elbow joint. The patients had to perform rhythmic alternating flexion and extension movements in the elbow joint. The rhythm and spatial extent of movements were indicated acoustically by a click tone stimulator and by marks respectively. Six manoeuvres (spatial extents of 48 degrees , 83 degrees at frequencies of 0.9 Hz, 1.5 Hz, and 2.5 Hz each) had to be performed. A potentiometer converted the horizontal movements of the forearm into a variable voltage. Forearm movements were measured with and without contralateral VIM stimulation. In all patients, spatial accuracy of the alternating forearm movements improved significantly after the stimulation had been switched on. Temporal accuracy increased during VIM stimulation in 5 of 6 patients. In 1 of 6 patients the spatial but not the temporal movement accuracy improved during stimulation. During VIM stimulation, performance of alternating forearm movements improved significantly. This might indicate that VIM stimulation could be a therapeutic alternative in the treatment of upper limb ataxia in MS.

Long-term deep brain stimulation in elderly patients with cardiac pacemakers

Deep brain stimulation (DBS) has become an accepted therapy for movement disorders such as Parkinson disease (PD) and essential tremor (ET), when these conditions are refractory to medical treatment. The presence of a cardiac pacemaker is still considered a contraindication for DBS in functional neurosurgery. The goal of this study was to evaluate the technical and clinical management of DBS for the treatment of movement disorders in elderly patients with cardiac pacemakers. Six patients with cardiac pacemakers underwent clinical and cardiac examinations to analyze the safety of DBS in the treatment of movement disorders. Four patients suffered from advanced PD and two patients had ET. The mean age of these patients at surgery was 69.5 years (range 63-79 years). The settings of the pacemakers were programmed in a manner considered to minimize the chance of interference between the two systems. There were no adverse events during surgery. Four patients underwent stimulation of the thalamic ventralis intermedius nucleus (VIM), and two patients stimulation of the subthalamic nucleus. In general, bipolar sensing was chosen for the cardiac pacemakers. In all but one patient the quadripolar DBS electrodes were programmed for bipolar stimulation. Several control electrocardiography studies, including 24-hour monitoring, did not show any interference between the two systems. At the time this paper was written the patients had been followed up for a mean of 25.3 months (range 4-48 months). In certain conditions it is safe for patients with cardiac pacemakers to receive DBS for treatment of concomitant movement disorders. Cardiac pacemakers should not be viewed as a general contraindication for DBS in patients with movement disorders.

Gamma knife thalamotomy for movement disorders: evaluation of the thalamic lesion and clinical results

The authors studied the effects of gamma knife thalamotomy (GKT) on Parkinson disease-related tremor and essential tremor before and after reloading of radioactive cobalt. Based on experience in stereotactic thalamotomy aided by depth microrecording, the target was located at the lateral border of the thalamic ventralis intermedius nucleus (VIM). For more precise targeting, the percentage representation of the thalamic VIM in relation to the entire thalamic length is useful. The location of the target was determined on magnetic resonance (MR) imaging and computerized tomography scanning. A maximum dose of 130 Gy was delivered to the target by using a single isocenter with the 4-mm collimator. In more recent cases, a systematic follow-up examination was performed at 3, 6, 12, 18, and 24 months after GKT. Since 1993, the authors have treated 70 patients with PD. Throughout the series the same dosimetric technique has been used. The course after GKT was compared between the 25 cases with PD treated before reloading and the 35 cases treated after reloading. In the majority (80-85%) treated after reloading, tremor and rigidity were reduced around 6 months after GKT. In the cases treated before reloading this effect took approximately 1 year. The thalamic reaction on MR imaging showed the same two lesion types in both series: a restricted and a diffuse. After reloading the restricted lesion was more frequent and the lesion volume was smaller. The shorter delay in clinical improvement and smaller lesion size may be related to an increased radiation dose.

Gamma knife thalamotomy for movement disorders: evaluation of the thalamic lesion and clinical results

Object. The authors studied the effects of gamma knife thalamotomy (GKT) on Parkinson disease-related tremor and essential tremor before and after reloading of radioactive cobalt. Methods. Based on experience in stereotactic thalamotomy aided by depth microrecording, the target was located at the lateral border of the thalamic ventralis intermedius nucleus (VIM). For more precise targeting, the percentage representation of the thalamic VIM in relation to the entire thalamic length is useful. The location of the target was determined on magnetic resonance (MR) imaging and computerized tomography scanning. A maximum dose of 130 Gy was delivered to the target by using a single isocenter with the 4-mm collimator. In more recent cases, a systematic follow-up examination was performed at 3, 6, 12, 18, and 24 months after GKT. Since 1993, the authors have treated 70 patients with PD. Throughout the series the same dosimetric technique has been used. The course after GKT was compared between the 25 cases with PD treated before reloading and the 35 cases treated after reloading. In the majority (80–85%) treated after reloading, tremor and rigidity were reduced around 6 months after GKT. In the cases treated before reloading this effect took approximately 1 year. The thalamic reaction on MR imaging showed the same two lesion types in both series: a restricted and a diffuse. After reloading the restricted lesion was more frequent and the lesion volume was smaller. Conclusions. The shorter delay in clinical improvement and smaller lesion size may be related to an increased radiation dose.

Model Based Development of Novel Deep Brain Stimulation Techniques

Pathological synchronization is a hallmark of several neurological diseases like Parkinson's disease (PD) or essential tremor [Alberts et al., Nature 1969; 221: 670; Nini et al., J Neurophys 1995; 74: 1800]. For example, a pacemaker-like population of neurons, which fires in a synchronized and periodical manner, provokes the Parkinsonian resting tremor [Alberts et al., Nature 1969; 221: 670]. In contrast, an uncorrelated, i.e., desynchronized firing pattern of these neuronal populations is characteristic in healthy subjects [Nini et al., J Neurophys 1995; 74: 1800]. In medically intractable patients, electrical deep brain stimulation (DBS) is administered via depth electrodes chronically implanted in the subthalamic nucleus of the thalamic ventralis intermedius nucleus [Benabid et al., Lancet 1991; 337: 403]. For that purpose, a permanent high-frequency (>100Hz) periodic pulse train stimulation is used. Up to now the mechanism of high-frequency DBS is not yet sufficiently understood [Benabid et al., Lancet 1991; 337: 403]. We initiated a model-based development of novel stimulation protocols to find milder and more effective DBS techniques [Tass, Phase Resetting in Medicine and Biology, Springer, 1999; Tass, Biol Cyb 2003; 89: 81]. In a first clinical study performed during electrode implantation, we have shown that the coordinated reset via multiple/several sites can suppress the peripheral tremor, even if the standard high-frequency DBS has no tremor suppressive effect at all [Tass et al., submitted (2004)]. Here we present a technique for the desynchronization of a strongly synchronized target population which we expect to be even more effective and milder. For this, delayed mean field potentials are administered at different sites within a neuronal population to establish a desynchronized state. According to detailed theoretical investigations and simulations, we expect the novel desynchronization technique to be considerably milder, to act in a demand-controlled way and to be simple in realization. We use a microscopic model of a neuronal population in a relevant target area to show that the method is robust and does not require time consuming calibration. It is suggested that the novel technique is used for deep brain stimulation in patients suffering from Parkinson's disease, essential tremor or epilepsy.

Dynamic studies on the thalamocortical relation involved in tremor and voluntary movement in Parkinson's disease using PET and depth microrecording

Resting regional cerebral glucose metabolism (rCMRGlu) and cerebral blood flow (rCBF) were measured using positron emission tomography (PET) scan in seven cases with hemitremor type Parkinson's disease (PD). Regional CBF studies were also performed during unilateral sequential opposite finger movement (SOFM) on the side ipsilateral or contralateral to the tremor in each of the two cases. It was carried out on both sides in three cases. During the course of stereotactic thalamotomy with the aid of depth microrecording, rhythmic burst discharges synchronous with peripheral tremors were recorded in thalamic nucleus ventralis intermedius (VIM) in all the cases except one. In six out of the seven cases, the spot-shaped increased zone of rCMRGlu and/or rCBF was found in the precentral area on the side contralateral to the tremor. In all the five cases, SOFM contralateral to the tremor caused the increase of rCBF in the contralateral precentral area. While in two out of the five cases, SOFM ipsilateral to the tremor evoked an increase of rCBF in the bilateral precentral areas. It was postulated that both thalamic VIM and the frontal precentral area might play important roles in mediating and maintaining tremor in cases with PD. Voluntary hand movement on the side ipsilateral to the tremor often caused precentral cortical activation on both sides.

Evaluation of gamma thalamotomy for parkinsonian and other tremors: survival of neurons adjacent to the thalamic lesion after gamma thalamotomy

Object. The effects of gamma thalamotomy for parkinsonian and other kinds of tremor were evaluated. Methods. Thirty-six thalamotomies were performed in 31 patients by using a 4-mm collimator. The maximum dose was 150 Gy in the initial six cases, which was reduced to 130 Gy thereafter. The longest follow-up period was 6 years. The target was determined on T2-weighted and proton magnetic resonance (MR) images. The point chosen was in the lateral-most part of the thalamic ventralis intermedius nucleus. This is in keeping with open thalamotomy as practiced at the authors' institution. In 15 cases, gamma thalamotomy was the first surgical procedure. In other cases, previous therapeutic or vascular lesions were visible to facilitate targeting. Two types of tissue reaction were onserved on MR imaging: a simple oval shape and a complex irregular shape. Neither of these changes affected the clinical course. In the majority of cases, the tremor subsided after a latent interval of approximately 1 year after irradiation. The earliest response was demonstrated at 3 months. In five cases the tremor remained. In four of these cases, a second radiation session was administered. One of these four patients as well as another patient with an unsatisfactory result underwent open thalamotomy with microrecording. In both cases, depth recording adjacent to the necrotic area revealed normal neuronal activity, including the rhythmic discharge of tremor. Minor coagulation was performed and resulted in immediate and complete arrest of the remaining tremor. Conclusions. Gamma thalamotomy for Parkinson's disease seems to be an alternative useful method in selected cases.

Chronic Electrical Stimulation of the Ventralis Intermedius Nucleus of the Thalamus and of Other Nuclei as a Treatment for Parkinsonʼs Disease

Abstract:During stereotaxy in nonanesthetized patients with Parkinson's disease or essential tremor, tremor was suppressed by test stimulation of the thalamic ventralis intermedius nucleus (Vim) at high frequency (130 Hz). Based on this finding, the authors have used chronic stimulation of the Vim a

Effect of electrical stimulation of the thalamic Vim nucleus on hand tremor during stereotactic thalamotomy

Objective: The aim of this study was to analyze the correlation between neuronal responses in the thalamic ventralis intermedius (Vim) nucleus to peripheral, natural stimulation and the modulation of tremor by electrical stimulation during stereotactic thalamotomy. Design and methods: The authors studied 36 patients with hand tremor using a microelectrode. The responses of tremor to electrical stimulation were analysed electromyographically. Sixty stimulation sites were divided into three groups. Results: Group A (20 sites) where responses to stretching of the contralateral forearm muscles were recorded. Group B (26 sites) where responses to stretching of the other muscles of the upper extremity were recorded. Electrical stimulation at sites in groups A and B temporarily suppressed the contralateral tremor, but the minimum current intensity to suppress tremor at sites in group A was less than that in group B. Electrical stimulation in group C (14 sites), where kinesthetic responses of contralateral lower extremity were recorded, resulted in increased amplitude of hand tremor. Selective coagulation including the area of tremor suppression resulted in abolition of the tremor in all patients. Conclusions: These results suggest that the most effective site for thalamotomy may also be suitable for chronic stimulation in the Vim nucleus.

Chronic electrical stimulation of the ventralis intermedius nucleus of the thalamus as a treatment of movement disorders

Tremor was suppressed by test stimulation of the thalamic ventralis intermedius (VIM) nucleus at high frequency (130 Hz) during stereotaxy in nonanesthetized patients suffering from Parkinson's disease or essential tremor. Ventralis intermedius stimulation has since been used by the authors over the last 8 years as a treatment in 117 patients with movement disorders (80 cases of Parkinson's disease, 20 cases of essential tremor, and 17 cases of various dyskinesias and dystonias including four multiple sclerosis). Chronic electrodes were stereotactically implanted in the VIM and connected to a programmable stimulator. Results depend on the indication. In Parkinson's disease patients, tremor, but not bradykinesia and rigidity, was selectively suppressed for as long as 8 years. Administration of L-Dopa was decreased by more than 30% in 40 Parkinson's disease patients. In essential tremor patients, results were satisfactory but deteriorated with time in 18.5% of cases, mainly for patients who presented an action component of their but deteriorated with time in 18.5% of cases, mainly for patients who presented an action component of their tremor. In other types of dyskinesias (except multiple sclerosis), results were much less favorable. Fifty-nine patients underwent bilateral implantation and 14 other patients received implantation contralateral to a previous thalamotomy. Thirty-seven patients (31.6%) experienced minor side effects, which were always well tolerated and immediately reversible. Three secondary scalp infections led to temporary removal of the implanted material. There was no permanent morbidity. This tremor suppression effect could be due to the inhibition or jamming of a retroactive loop. Chronic VIM stimulation, which is reversible, adaptable, and well tolerated even by patients undergoing bilateral surgery (74 of 117 patients) and by elderly patients, should replace thalamotomy in the regular surgical treatment of parkinsonian and essential tremors.

Further physiological observations on the ventralis intermedius neurons in the human thalamus.

1. During the course of stereotaxic thalamotomy for 56 cases with tremor mainly due to Parkinson's disease and essential tremor, extracellular recordings were made from the thalamic ventralis intermedius (Vim) nucleus under local anesthesia. These procedures have been justified as an essential technique to achieve the best therapeutic results by a selective coagulation. These physiological observations provide important information about the functional organization of the ventrolateral thalamic mass in humans. 2. Using Leksell's stereotaxic apparatus, a pair of semimicroelectrodes was introduced simultaneously to the thalamic ventral lateral region from the prefrontal area. The Vim nucleus was identified tentatively by characteristic high background activity which contrasted to that found in its rostral part and by superimposed large amplitude spontaneously active units. 3. In this high activity zone, 135 units (approximately 1/5 of the recorded units) responded to natural stimulation applied to contralateral body parts. Among them, approximately 90% responded to a passive or active movement of a joint. Several lines of evidence suggested that probably muscle receptors were responsible. 4. The rest of units (approximately 10%) responded to light touch applied to contralateral skin surface. Convergent responses between kinesthetic and tactile units were never encountered. Also, kinesthetic and tactile neurons were geographically separated. The latter were found always at the end of our oblique trajectory, following the kinesthetic neurons. 5. Neurons with sensory responses were clustered mostly within the confines of the Vim nucleus, probably extending caudally to the ventrocaudalis externus anterior of Hassler. Evidence for a somatotopic representation in the Vim nucleus was obtained. 6. Electrical stimulation of the appropriate peripheral nerve produced responses of the same thalamic unit(s) that responded to natural stimulation. The latency to upper limb nerve stimulation was between approximately 10 and 20 ms. It was almost fixed in a given case. 7. It is concluded that the Vim nucleus receives kinesthetic afferent input from the contralateral body parts (mainly from the muscle receptor) and may be concerned with muscle sense. This may explain why a small, selective coagulation of the physiologically identified Vim has such a constant effect on several different kinds of tremor.