Neuroanatomical considerations for optimizing thalamic deep brain stimulation in Tourette syndrome.

OBJECTIVE: Deep brain stimulation (DBS) of the centromedian thalamic nucleus has been reportedly used to treat severe Tourette syndrome, yielding promising outcomes. However, it remains unclear how DBS electrode position and stimulation parameters modulate the specific area and related networks. The authors aimed to evaluate the relationships between the anatomical location of stimulation fields and clinical responses, including therapeutic and side effects. METHODS: The authors collected data from 8 patients with Tourette syndrome who were treated with DBS. The authors selected the active contact following threshold tests of acute side effects and gradually increased the stimulation intensity within the therapeutic window such that acute and chronic side effects could be avoided at each programming session. The patients were carefully interviewed, and stimulation-induced side effects were recorded. Clinical outcomes were evaluated using the Yale Global Tic Severity Scale, the Yale-Brown Obsessive-Compulsive Scale, and the Hamilton Depression Rating Scale. The DBS lead location was evaluated in the normalized brain space by using a 3D atlas. The volume of tissue activated was determined, and the associated normative connective analyses were performed to link the stimulation field with the therapeutic and side effects. RESULTS: The mean follow-up period was 10.9 ± 3.9 months. All clinical scales showed significant improvement. Whereas the volume of tissue activated associated with therapeutic effects covers the centromedian and ventrolateral nuclei and showed an association with motor networks, those associated with paresthesia and dizziness were associated with stimulation of the ventralis caudalis and red nucleus, respectively. Depressed mood was associated with the spread of stimulation current to the mediodorsal nucleus and showed an association with limbic networks. CONCLUSIONS: This study addresses the importance of accurate implantation of DBS electrodes for obtaining standardized clinical outcomes and suggests that meticulous programming with careful monitoring of clinical symptoms may improve outcomes.

Ventralis intermedius nucleus anatomical variability assessment by MRI structural connectivity.

The ventralis intermedius nucleus (Vim) is centrally placed in the dentato-thalamo-cortical pathway (DTCp) and is a key surgical target in the treatment of severe medically refractory tremor. It is not visible on conventional MRI sequences; consequently, stereotactic targeting currently relies on atlas-based coordinates. This fails to capture individual anatomical variability, which may lead to poor long-term clinical efficacy. Probabilistic tractography, combined with known anatomical connectivity, enables localisation of thalamic nuclei at an individual subject level. There are, however, a number of confounds associated with this technique that may influence results. Here we focused on an established method, using probabilistic tractography to reconstruct the DTCp, to identify the connectivity-defined Vim (cd-Vim) in vivo. Using 100 healthy individuals from the Human Connectome Project, our aim was to quantify cd-Vim variability across this population, measure the discrepancy with atlas-defined Vim (ad-Vim), and assess the influence of potential methodological confounds. We found no significant effect of any of the confounds. The mean cd-Vim coordinate was located within 1.88 mm (left) and 2.12 mm (right) of the average midpoint and 3.98 mm (left) and 5.41 mm (right) from the ad-Vim coordinates. cd-Vim location was more variable on the right, which reflects hemispheric asymmetries in the probabilistic DTC reconstructed. The method was reproducible, with no significant cd-Vim location differences in a separate test-retest cohort. The superior cerebellar peduncle was identified as a potential source of artificial variance. This work demonstrates significant individual anatomical variability of the cd-Vim that atlas-based coordinate targeting fails to capture. This variability was not related to any methodological confound tested. Lateralisation of cerebellar functions, such as speech, may contribute to the observed asymmetry. Tractography-based methods seem sensitive to individual anatomical variability that is missed by conventional neurosurgical targeting; these findings may form the basis for translational tools to improve efficacy and reduce side-effects of thalamic surgery for tremor.

The synaptic inputs and thalamic projections of two classes of layer 6 corticothalamic neurons in primary somatosensory cortex of the mouse.

Although corticothalamic neurons (CThNs) represent the largest source of synaptic input to thalamic neurons, their role in regulating thalamocortical interactions remains incompletely understood. CThNs in sensory cortex have historically been divided into two types, those with cell bodies in Layer 6 (L6) that project back to primary sensory thalamic nuclei and those with cell bodies in Layer 5 (L5) that project to higher-order thalamic nuclei and subcortical structures. Recently, diversity among L6 CThNs has increasingly been appreciated. In the rodent somatosensory cortex, two major classes of L6 CThNs have been identified: one projecting to the ventral posterior medial nucleus (VPM-only L6 CThNs) and one projecting to both VPM and the posterior medial nucleus (VPM/POm L6 CThNs). Using rabies-based tracing methods in mice, we asked whether these L6 CThN populations integrate similar synaptic inputs. We found that both types of L6 CThNs received local input from somatosensory cortex and thalamic input from VPM and POm. However, VPM/POm L6 CThNs received significantly more input from a number of additional cortical areas, higher order thalamic nuclei, and subcortical structures. We also found that the two types of L6 CThNs target different functional regions within the thalamic reticular nucleus (TRN). Together, our results indicate that these two types of L6 CThNs represent distinct information streams in the somatosensory cortex and suggest that VPM-only L6 CThNs regulate, via their more restricted circuits, sensory responses related to a cortical column while VPM/POm L6 CThNs, which are integrated into more widespread POm-related circuits, relay contextual information.

Probabilistic tractography in the ventrolateral thalamic nucleus: cerebellar and pallidal connections.

The ventrolateral thalamic nucleus (VL), as part of the 'motor thalamus', is main relay station of cerebellar and pallidal projections. It comprises anterior (VLa) and posterior (VLpd and VLpv) subnuclei. Though the fibre architecture of cerebellar and pallidal projections to of the VL nucleus has already been focus in a numerous amount of in vitro studies mainly in animals, probabilistic tractography now offers the possibility of an in vivo comparison in healthy humans. In this study we performed a (a) qualitative and (b) quantitative examination of VL-cerebellar and VL-pallidal pathways and compared the probability distributions between both projection fields in the VL after an (I) atlas-based and (II) manual-based segmentation procedure. Both procedures led to high congruent results of cerebellar and pallidal connectivity distributions: the maximum of pallidal projections was located in anterior and medial parts of the VL nucleus, whereas cerebellar connectivity was more located in lateral and posterior parts. The median connectivity for cerebellar connections in both approaches (manual and atlas-based segmentation) was VLa > VLpv > VLpd, whereas the pallidal median connectivity was VLa ~ VLpv > VLpd in the atlas-based approach and VLpv > VLa > VLpd in the manual approach.

Thalamic Deep Brain Stimulation for tremor: The critical role of intraoperative testing.

INTRODUCTION: Optimal placement of Deep Brain Stimulation (DBS) lead is critical to ensure an adequate therapeutic benefit and minimize stimulation-induced side effects. METHODS: We reviewed data from 2004 to 2018 of all cases of essential tremor treated with thalamic DBS at the University of Cincinnati. All procedures were performed with the patient awake. Change in parallel trajectory was classified as major repositioning, whereas a change in depth of electrode classified as minor repositioning. The following data were compared between groups (no vs. minor vs. major repositioning): age at surgery, sex, AC-PC length, third ventricle width, cerebral atrophy, small vessel disease burden, and intraoperative tremor control. Univariate and multivariate analyses were conducted to identify factors associated with intraoperative repositioning. RESULTS: Of the 127 encounters with essential tremor, 71 required repositioning (33 major and 38 minor). Comparing procedures with major, minor, and no repositioning, mean number of changes per procedure (4 vs. 1.2 vs 0; p < 0.001) and AC-PC length (26 vs. 27 vs. 27.2 mm; p = 0.021) differed between the three groups. Older age at surgery (OR 1.04, p = 0.042), left side (OR 2.56, p = 0.04) and decrease in AC-PC length (OR 1.33, p = 0.026) were associated with greater odds of any (minor or major) repositioning. A decrease in AC-PC length was associated with greater odds of major repositioning (OR 1.37, p = 0.009). CONCLUSION: Intraoperative functional testing may be critical to ensure the accuracy of thalamic DBS targeting based on neuroimaging data, particularly in patients with reduced AC-PC length.

Arterial Supply of the Thalamus: A Comprehensive Review.

The thalamus is a deep cerebral structure that is crucial for proper neurological functioning as it transmits signals from nearly all pathways in the body. Insult to the thalamus can, therefore, result in complex syndromes involving sensation, cognition, executive function, fine motor control, emotion, and arousal, to name a few. Specific territories in the thalamus that are supplied by deep cerebral arteries have been shown to correlate with clinical symptoms. The aim of this review is to enhance our understanding of the arterial anatomy of the thalamus and the complications that can arise from lesions to it by considering the functions of known thalamic nuclei supplied by each vascular territory.

Spatial scale of receptive fields in the visual sector of the cat thalamic reticular nucleus.

Inhibitory projections from the visual sector of the thalamic reticular nucleus to the lateral geniculate nucleus complete the earliest feedback loop in the mammalian visual pathway and regulate the flow of information from retina to cortex. There are two competing hypotheses about the function of the thalamic reticular nucleus. One regards the structure as a thermostat that uniformly regulates thalamic activity through negative feedback. Alternatively, the searchlight hypothesis argues for a role in focal attentional modulation through positive feedback, consistent with observations that behavioral state influences reticular activity. Here, we address the question of whether cells in the reticular nucleus have receptive fields small enough to provide localized feedback by devising methods to quantify the size of these fields across visual space. Our results show that reticular neurons in the cat operate over discrete spatial scales, at once supporting the searchlight hypothesis and a role in feature selective sensory processing.The searchlight hypothesis proposes that the thalamic reticular nucleus regulates thalamic relay activity through focal attentional modulation. Here the authors show that the receptive field sizes of reticular neurons are small enough to provide localized feedback onto thalamic neurons in the visual pathway.

Anatomic Targeting of the Optimal Location for Thalamic Deep Brain Stimulation in Patients with Essential Tremor.

BACKGROUND: Thalamic deep brain stimulation (DBS) is an effective strategy for treatment of essential tremor (ET). With limitations of imaging modalities, targeting largely relies on indirect methods. This study was designed to determine the optimal target for DBS in ET and construct a targeting method based on probabilistic maps. METHODS: Patients with ET who had sustained tremor reduction at 1 year and optimal microelectrode recordings were selected. Stimulation volume was individually modeled in standard space, and a final optimal region was derived for the whole population. A fornix (FX) targeting method was developed to determine the location of the optimal stimulation site relative to the FX and posterior commissure (PC) in the anteroposterior plane, the border between the thalamus and internal capsule in the mediolateral plane, and the anterior commissure (AC)-PC (AC-PC) plane in the dorsoventral axis. Following comparative analyses with other standard indirect methods (25% of AC-PC and PC + 6 mm), the FX method was studied in relation to diffusion tensor imaging. RESULTS: Using the FX method, the optimal stimulation site was at the intersection of two thirds and one third of the PC-FX distance (mean of 28% ± 1.5 AC-PC length) and 4 mm medial to the lateral border of the thalamus. Compared with previously used methods, there was a significant reduction in variability of the optimal stimulation site with the FX method. The target defined using this strategy was found to be within the boundaries of the dentatorubrothalamic tract. CONCLUSIONS: The FX method may be an additional targeting strategy in patients undergoing thalamic DBS surgery.

Prenatal thalamic waves regulate cortical area size prior to sensory processing.

The cerebral cortex is organized into specialized sensory areas, whose initial territory is determined by intracortical molecular determinants. Yet, sensory cortical area size appears to be fine tuned during development to respond to functional adaptations. Here we demonstrate the existence of a prenatal sub-cortical mechanism that regulates the cortical areas size in mice. This mechanism is mediated by spontaneous thalamic calcium waves that propagate among sensory-modality thalamic nuclei up to the cortex and that provide a means of communication among sensory systems. Wave pattern alterations in one nucleus lead to changes in the pattern of the remaining ones, triggering changes in thalamic gene expression and cortical area size. Thus, silencing calcium waves in the auditory thalamus induces Rorß upregulation in a neighbouring somatosensory nucleus preluding the enlargement of the barrel-field. These findings reveal that embryonic thalamic calcium waves coordinate cortical sensory area patterning and plasticity prior to sensory information processing.

Importance of the ventral midline thalamus in driving hippocampal functions.

The ventral midline of the thalamus encompasses the reuniens and rhomboid (ReRh) nuclei. These nuclei are bidirectionally connected with the hippocampus and the medial prefrontal cortex (mPFC). About 8% of the neurons of the Re have collaterals in both structures. The ReRh nuclei provide the major thalamic input to the hippocampus. Their stimulation induces long-term potentiation in region CA1, suggesting a role in hippocampal plasticity. Experimental manipulations of the ReRh nuclei such as lesions, reversible inactivations, or optogenetic stimulations produce alterations of cognitive functions, especially in tasks known for their sensitivity to lesions of the hippocampus, but also of the mPFC. Behavioral approaches suggest that the ReRh nuclei might relay incoming signals from the mPFC both to the hippocampus and back to the mPFC. Thus, the Re and Rh nuclei have a role in orchestrating the information flow between the hippocampus and the mPFC, and this orchestration has both "online" and "off-line" implications in cognitive functions.

Contralateral cerebello-thalamo-cortical pathways with prominent involvement of associative areas in humans in vivo.

In addition to motor functions, it has become clear that in humans the cerebellum plays a significant role in cognition too, through connections with associative areas in the cerebral cortex. Classical anatomy indicates that neo-cerebellar regions are connected with the contralateral cerebral cortex through the dentate nucleus, superior cerebellar peduncle, red nucleus and ventrolateral anterior nucleus of the thalamus. The anatomical existence of these connections has been demonstrated using virus retrograde transport techniques in monkeys and rats ex vivo. In this study, using advanced diffusion MRI tractography we show that it is possible to calculate streamlines to reconstruct the pathway connecting the cerebellar cortex with contralateral cerebral cortex in humans in vivo. Corresponding areas of the cerebellar and cerebral cortex encompassed similar proportion (about 80%) of the tract, suggesting that the majority of streamlines passing through the superior cerebellar peduncle connect the cerebellar hemispheres through the ventrolateral thalamus with contralateral associative areas. This result demonstrates that this kind of tractography is a useful tool to map connections between the cerebellum and the cerebral cortex and moreover could be used to support specific theories about the abnormal communication along these pathways in cognitive dysfunctions in pathologies ranging from dyslexia to autism.

Topographically organized projection to posterior insular cortex from the posterior portion of the ventral medial nucleus in the long-tailed macaque monkey.

Prior anterograde tracing work identified somatotopically organized lamina I trigemino- and spinothalamic terminations in a cytoarchitectonically distinct portion of posterolateral thalamus of the macaque monkey, named the posterior part of the ventral medial nucleus (VMpo; Craig [2004] J. Comp. Neurol. 477:119-148). Microelectrode recordings from clusters of selectively thermoreceptive or nociceptive neurons were used to guide precise microinjections of various tracers in VMpo. A prior report (Craig and Zhang [2006] J. Comp. Neurol. 499:953-964) described retrograde tracing results, which confirmed the selective lamina I input to VMpo and the anteroposterior (head to foot) topography. The present report describes the results of microinjections of anterograde tracers placed at different levels in VMpo, based on the anteroposterior topographic organization of selectively nociceptive units and clusters over nearly the entire extent of VMpo. Each injection produced dense, patchy terminal labeling in a single coherent field within a distinct granular cortical area centered in the fundus of the superior limiting sulcus. The terminations were distributed with a consistent anteroposterior topography over the posterior half of the superior limiting sulcus. These observations demonstrate a specific VMpo projection area in dorsal posterior insular cortex that provides the basis for a somatotopic representation of selectively nociceptive lamina I spinothalamic activity. These results also identify the VMpo terminal area as the posterior half of interoceptive cortex; the anterior half receives input from the vagal-responsive and gustatory neurons in the basal part of the ventral medial nucleus.

Validation of connectivity-based thalamic segmentation with direct electrophysiologic recordings from human sensory thalamus.

Connectivity-based segmentation has been used to identify functional gray matter subregions that are not discernable on conventional magnetic resonance imaging. However, the accuracy and reliability of this technique has only been validated using indirect means. In order to provide direct electrophysiologic validation of connectivity-based thalamic segmentations within human subjects, we assess the correlation of atlas-based thalamic anatomy, connectivity-based thalamic maps, and somatosensory evoked thalamic potentials in two adults with medication-refractory epilepsy who were undergoing intracranial EEG monitoring with intrathalamic depth and subdural cortical strip electrodes. MRI with atlas-derived localization was used to delineate the anatomic boundaries of the ventral posterolateral (VPL) nucleus of the thalamus. Somatosensory evoked potentials with intrathalamic electrodes physiologically identified a discrete region of phase reversal in the ventrolateral thalamus. Finally, DTI was obtained so that probabilistic tractography and connectivity-based segmentation could be performed to correlate the region of thalamus linked to sensory areas of the cortex, namely the postcentral gyrus. We independently utilized these three different methods in a blinded fashion to localize the "sensory" thalamus, demonstrating a high-degree of reproducible correlation between electrophysiologic and connectivity-based maps of the thalamus. This study provides direct electrophysiologic validation of probabilistic tractography-based thalamic segmentation. Importantly, this study provides an electrophysiological basis for using connectivity-based segmentation to further study subcortical anatomy and physiology while also providing the clinical basis for targeting deep brain nuclei with therapeutic stimulation. Finally, these direct recordings from human thalamus confirm early inferences of a sensory thalamic component of the N18 waveform in somatosensory evoked potentials.

Contrasting connectivity of the ventralis intermedius and ventralis oralis posterior nuclei of the motor thalamus demonstrated by probabilistic tractography.

BACKGROUND: Targeting of the motor thalamus for the treatment of tremor has traditionally been achieved by a combination of anatomical atlases and neuroimaging, intraoperative clinical assessment, and physiological recordings. OBJECTIVE: To evaluate whether thalamic nuclei targeted in tremor surgery could be identified by virtue of their differing connections with noninvasive neuroimaging, thereby providing an extra factor to aid successful targeting. METHODS: Diffusion tensor tractography was performed in 17 healthy control subjects using diffusion data acquired at 1.5-T magnetic resonance imaging (60 directions, b value = 1000 s/mm, 2 × 2 × 2-mm³ voxels). The ventralis intermedius (Vim) and ventralis oralis posterior (Vop) nuclei were identified by a stereotactic neurosurgeon, and these sites were used as seeds for probabilistic tractography. The expected cortical connections of these nuclei, namely the primary motor cortex (M1) and contralateral cerebellum for the Vim and M1, the supplementary motor area, and dorsolateral prefrontal cortex for the Vop, were determined a priori from the literature. RESULTS: Tractogram signal intensity was highest in the dorsolateral prefrontal cortex and supplementary motor area after Vop seeding (P < .001, Wilcoxon signed-rank tests). High intensity was seen in M1 after seeding of both nuclei but was greater with Vim seeding (P < .001). Contralateral cerebellar signal was highest with Vim seeding (P < .001). CONCLUSION: Probabilistic tractography can depict differences in connectivity between intimate nuclei within the motor thalamus. These connections are consistent with published anatomical studies; therefore, tractography may provide an important adjunct in future targeting in tremor surgery.

A case of tremor reduction and almost complete ageusia under bilateral thalamic (VIM) deep brain stimulation in essential tremor--a therapeutic dilemma.

Essential tremor (ET) is a neurological disorder that can be treated effectively by means of bilateral thalamic ventral intermediate nucleus (VIM) deep brain stimulation (DBS). We present a rare case of stimulation-dependent reversible ageusia that poses a therapeutic dilemma on the one hand and serves as an instructive example to elucidate the as yet incompletely defined gustatory pathways on the other. A 69-year-old patient with successful reduction of his disabling upper extremity ET experienced an almost complete but during stimulation cessation reversible ageusia under bilateral VIM DBS. An evaluation of diffusion tensor (DTI) neuroimaging studies was performed in order to detect effective electrode positions and volumes of activated tissue (VTA) in relation to the medial lemniscus (ML) and dentato-rubro-thalamic tract (DRT). Repeated subjective gustometry was conducted with differential manipulation of stimulation settings. This case report stresses the importance of fiber tracts for DBS surgery. Reconciled with previous findings in lesion cases, we assume the coexistence of decussating and non-decussating fibers in the gustatory tract combined with hemispheric dominance in the processing of gustatory information. A therapeutic option for this dilemma may be a patient-selectable stimulation program or bipolar stimulation establishing a smaller ovoid VTA.

Medioventral part of the posterior thalamus in the mouse.

The posterior thalamus (Po) consists of heterogeneous groups of cells, which have not been clearly defined. In the present study, we focused on a part of the Po in the mouse brain, which is located caudally to the ventral posterior nucleus and rostromedially to the medial geniculate nucleus and shows distinct calretinin immunoreactivity. While we found the region had a considerable unity on the cytoarchitectural and histochemical grounds, it did not correspond to any particular nucleus but partially involved three structures in a widely used brain atlas (Franklin and Paxinos, 2008). Therefore, we tentatively designated the region as the medioventral part of the posterior thalamus (PoMV) and examined its anatomical features with immunohistochemistry and retrograde tract-tracing. The PoMV was appreciated as a reticular structure with prominent calretinin immunoreactivity, especially in horizontal sections, and displayed apparent differences in the cytoarchitecture from its surrounding regions. The PoMV had two divisions: the dorsal division (PoMVd), which contained parvalbuminimmunoreactive fibers, and the ventral division (PoMVv), which lacked these fibers. The tract-tracing studies showed that the somata retrogradely labeled from the injections in the insular cortex and some of the extended amygdalar regions were fairly concentrated within the PoMV, especially in the PoMVd. On the other hand, the labeling from the medial hypothalamus injections was found predominantly within the PoMVv. These findings indicate that the PoMV can be regarded as a distinct structure within the Po, and it may play a role in the emotional aspect of somatosensory processing.

Deep brain stimulation in benign tremulous parkinsonism.

BACKGROUND: Benign tremulous parkinsonism (BTP) is characterized by prominent resting plus action tremor, mild parkinsonism with limited disability or progression apart from tremor, and a less-robust response to levodopa therapy. This disorder has an uncertain pathophysiologic relationship to idiopathic Parkinson disease. Deep brain stimulation (DBS) should be efficacious for this condition, but there is no previously published experience. OBJECTIVES: To assess the clinical outcomes and surgical complications of patients with BTP who underwent DBS. DESIGN: Retrospective case series. SETTING: Tertiary care medical center. PATIENTS: Twelve men and 3 women with BTP who underwent DBS for levodopa-refractory tremor. MAIN OUTCOME MEASURES: Tremor status after DBS, preoperative vs postoperative scores on the Fahn-Tolosa-Marin tremor scale, and the presence of adverse events. RESULTS: Of the 15 patients, 8 underwent unilateral thalamic nucleus ventralis intermedius (VIM), 4 bilateral VIM, and 3 bilateral subthalamic nucleus DBS. At last follow-up at a median of 4 years post-DBS, 7 patients were tremor free, 6 had only trace tremor, and 2 were definitely improved but with residual tremor. The median preoperative Fahn-Tolosa-Marin tremor scale score was 17 (range, 11-21); the tremor scale score at the last videotaped follow-up was 1 (range, 0-6). Median time between the 2 videotapes was 11.5 months (range, 3-14 months). No patients experienced adverse events after the surgical procedure. CONCLUSIONS: These findings support the efficacy of DBS, with VIM and STN targets, in medically refractory BTP-related tremor. Further studies are needed to explore the long-term durability of response and to better compare the surgical targets.

Diffusion tensor imaging and colored fractional anisotropy mapping of the ventralis intermedius nucleus of the thalamus.

BACKGROUND: The ventralis intermedius (VIM) nucleus of the thalamus is the primary surgical target for treatment of tremor. Most centers rely on indirect targeting based on atlas-defined coordinates rather than patient-specific anatomy, making intraoperative physiological mapping critical. Detailed identification of this target based on patient-specific anatomic features can help optimize the surgical treatment of tremor. OBJECTIVE: To study colored fractional anisotropic images and diffusion tensor imaging (DTI) tractography to identify characteristic magnetic resonance appearances of the VIM nucleus. METHODS: Four patients undergoing stereotactic surgery for essential tremor (ET) were retrospectively studied with analysis of magnetic resonance imaging-based colored fractional anisotropy (FA) images and fiber tractography. All were scanned with a 1.5-T magnetic resonance imaging unit, and all sequences were obtained before frame placement. Because the goal of this study was to identify the DTI characteristics of physiologically defined VIM nucleus, we selected and studied patients who had undergone DTI and had efficacious tremor control with intraoperative microlesioning effect and tremor reduction with less than 2.0-V stimulation. RESULTS: Analysis of color FA maps, which graphically illustrate fiber directionality, revealed consistent anatomic patterns. The region of the VIM nucleus can be seen as an intermediate region where there is a characteristic transition of color. Presumptive VIM nucleus interconnectivity with sensorimotor cortex and cerebellum was identified via the internal capsule and the superior cerebellar peduncle, respectively. FA maps could also be used to distinguish segments of gray matter, white matter, and gray-white matter boundaries. CONCLUSION: Analysis of DTI and FA maps on widely available 1.5-T magnetic resonance imaging yields clear identification of various structures key to neurosurgical targeting. Prospective evaluation of integrating DTI into neurosurgical planning may be warranted.

Probabilistic somatotopy of the spinothalamic pathway at the ventroposterolateral nucleus of the thalamus in the human brain.

BACKGROUND AND PURPOSE: The STP has been regarded as the most plausible neural tract responsible for pathogenesis of central poststroke pain. The VPL nucleus has been a target for neurosurgical procedures for control of central poststroke pain. However, to our knowledge, no DTI studies have been conducted to investigate the somatotopic location of the STP at the VPL nucleus of the thalamus. In the current study, we attempted to investigate this location in the human brain by using a probabilistic tractography technique of DTI. MATERIALS AND METHODS: DTI was performed at 1.5T by using a Synergy-L SENSE head coil. STPs for both the hand and leg were obtained by selection of fibers passing through 2 regions of interest (the area of the spinothalamic tract in the posterolateral medulla and the postcentral gyrus) for 41 healthy volunteers. Somatotopic mapping was obtained from the highest probabilistic location at the ACPC level. RESULTS: The highest probabilistic locations for the hand and leg were an average of 16.86 and 16.37 mm lateral to the ACPC line and 7.53 and 8.71 mm posterior to the midpoint of the ACPC line, respectively. Somatotopic locations for the hand and leg were different in the anteroposterior direction (P < .05); however, no difference was observed in the mediolateral direction (P > .05). CONCLUSIONS: We found the somatotopic locations for hand and leg of the STP at the VPL nucleus; these somatotopies were arranged in the anteroposterior direction.

Deep brain stimulation of the ventral intermediate nucleus in patients with essential tremor: stimulation below intercommissural line is more efficient but equally effective as stimulation above.

BACKGROUND: The posterior subthalamic area (PSA), ventral to the intercommissural line (ICL) and the ventral intermediate nucleus (VIM), has been suggested as a promising target for deep brain stimulation (DBS) in patients suffering from essential tremor (ET). In this study the clinical benefit of VIM and PSA DBS on postural tremor suppression was systematically evaluated in a two step approach with a 3D ultrasound kinematic analysis tool. METHODS: We defined the exact position of 40 VIM-DBS-electrodes from 21 ET patients. In a first experiment with a subgroup of electrodes we subsequently activated a thalamic and a contact below ICL (sub-ICL) with equal parameter settings for within subject comparison. In a second step, we divided all electrodes into two groups, i.e. one group with activated thalamic and the other group with activated contacts below ICL and performed a group comparison under patients' individual stimulation parameters. Here, the corrected amplitude required for tremor suppression was analyzed separately for both groups. RESULTS: Within subject comparison with equal parameter settings revealed a significant improvement of sub-ICL compared to thalamic stimulation. In contrast, group comparison under patients' individual stimulation did not show any significant difference in tremor suppression between VIM and PSA DBS. Although higher corrected stimulation amplitude was needed in the thalamic group this difference was not significant. CONCLUSION: The data suggest that sub-ICL stimulation may be more efficient compared to thalamic stimulation but equally effective when patients' individual stimulation parameters are used.