Statistical determination of the optimal subthalamic nucleus stimulation site in patients with Parkinson disease

OBJECT: The subthalamic nucleus (STN) is currently recognized as the preferred target for deep brain stimulation (DBS) in patients with Parkinson disease (PD). If there is agreement in the literature that DBS improves motor symptoms significantly, the situation is less clear with respect to the side effects of this procedure. The goal of this study was to correlate the coordinate values of active electrode contacts with the amplitude of residual clinical symptoms and side effects using a mathematical approach. METHODS: In this study the investigators examined a cohort of 41 patients with PD who received clinical benefits from DBS after stimulating electrodes had been implanted bilaterally into the STN. The combined scores of residual clinical symptoms plus side effects, including speech disturbance, postural instability, and weight gain, were fitted by using either inverted ellipsoidal exponefitials or smooth splines. These analyses showed evidence of lower combined scores for stimulating contacts at an x coordinate approximately 12.0 to 12.3 mm lateral to the anterior commissure-posterior commissure (AC-PC) line and at a z coordinate approximately 3.1 to 3.3 mm under the AC-PC line. There was insufficient evidence for a preferred y coordinate location. CONCLUSIONS: The authors propose a "best" therapeutic ellipse area that is centered at an x, z location of 12.5 mm, -3.3 mm and characterized by an extension of 1.85 mm in the x direction and 2.22 mm in the z direction. Therapeutic electrode contacts located within this area are well correlated with the lowest occurrence of residual symptoms and the lowest occurrence of side effects independent of STN anatomical considerations. The lack of a significant result in the y direction remains to be explored further.     

Subthalamic deep brain stimulation for severe idiopathic Parkinson's disease. Location study of the effective contacts

The subthalamic nucleus (STN) is the main target of deep brain stimulation (DBS) treatment for severe idiopathic Parkinson's disease. But there is still no clear information on the location of the effective contacts (used during the chronic phase of stimulation). Our aim was to assess the anatomical structures of the subthalamic area (STA) involved during chronic DBS. Ten patients successfully treated were included. The surgical procedure was based on direct STN targeting (stereotactic MRI based) pondered by the acute effects of intraoperative stimulation. We used a formaldehyde-fixed human specimen to compare by matching MRI images obtained at 1.5 Tesla (performed in clinical stereotactic conditions) and at very high field at 4.7 Tesla. This allowed accurate analysis of the anatomy of the STA and retrospective precision of the location of the center of effective contacts which were located within the STN in 4 patients, at the interface between the STN and the ZI and/or FF in 13, at the interface between ZI and FF in 2 and between the STN and the substantia nigra in one. These results were consistent with the literature, revealing the implication of neighboring structures, especially the zona incerta and Forel's Field, in the clinical benefit.     

Localization of stimulating electrodes in patients with Parkinson disease by using a three-dimensional atlas-magnetic resonance imaging coregistration method

OBJECT: The aim of this study was to correlate the clinical improvement in patients with Parkinson disease (PD) treated using deep brain stimulation (DBS) of the subthalamic nucleus (STN) with the precise anatomical localization of stimulating electrodes. METHODS: Localization was determined by superimposing figures from an anatomical atlas with postoperative magnetic resonance (MR) images obtained in each patient. This approach was validated by an analysis of experimental and clinical MR images of the electrode, and the development of a three-dimensional (3D) atlas-MR imaging coregistration method. The PD motor score was assessed through two contacts for each of two electrodes implanted in 10 patients: the "therapeutic contact" and the "distant contact" (that is, the next but one to the therapeutic contact). Seventeen therapeutic contacts were located within or on the border of the STN, most of which were associated with significant improvement of the four PD symptoms tested. Therapeutic contacts located in other structures (zona incerta, lenticular fasciculus, or midbrain reticular formation) were also linked to a significant positive effect. Stimulation applied through distant contacts located in the STN improved symptoms of PD, whereas that delivered through distant contacts in the remaining structures had variable effects ranging from worsening of symptoms to their improvement. CONCLUSIONS: The authors have demonstrated that 3D atlas-MR imaging coregistration is a reliable method for the precise localization of DBS electrodes on postoperative MR images. In addition, they have confirmed that although the STN is the main target during DBS treatment for PD, stimulation of surrounding regions, particularly the zona incerta or the lenticular fasciculus, can also improve symptoms of PD.     

Localization of electrodes in the subthalamic nucleus on magnetic resonance imaging

OBJECT: The authors describe a new method of localizing electrodes on magnetic resonance (MR) images and focus on the positions of both the most efficient contact and the electrode related to the MR imaging target. METHODS: Thirty-one patients who had undergone bilateral subthalamic nucleus (STN) deep brain stimulation (DBS) were included in this study. Target coordinates were calculated in the anterior commissure-posterior commissure referential. A study of the correlation between the artifact and the related contact allowed one to deduce the contact position from the identification of the distal artifact on MR imaging. The best stimulation point corresponded with the contact resulting in the best Unified Parkinson's Disease Rating Scale (UPDRS) motor score improvement. It was compared (Student t-test) with the dorsal margin of the STN (DM STN), which was determined electrophysiologically. The distance between the target and the electrode was calculated individually in each axis. The best stimulation point was located at anteroposterior -2.34 +/- 1.63 mm, lateral 12.04 +/- 1.62 mm, and vertical -2.57 +/- 1.68 mm. This point was not significantly different from the DM STN (p < 0.05). The postoperative UPDRS motor score was 28.07 +/- 12.16, as opposed to the preoperative score of 46.27 +/- 13.89. The distance between the expected and actual target in the x- and y-axes was 1.34 +/- 1.02 and 1.03 +/- 0.76 mm, respectively. In the z-axis, 39.7% of the distal contacts were located proximal to the target. CONCLUSIONS: This approach proposed for the localization of the electrodes on MR imaging shows that DBS is most effective in the dorsal and lateral part of the STN and indicates that the DBS electrode can be located more proximally than originally expected because of the caudal brain shift that may occur during the implantation procedure.     

Anatomical identification of active contacts in subthalamic deep brain stimulation

BACKGROUND: Subthalamic Deep Brain Stimulation is a valid surgical procedure for the treatment of idiopathic PD, although its precise mechanism of action is still unclear; moreover, there are no conclusive data about the functional anatomy of the human subthalamic region. Identifying the location of active contacts for StnDBS can yield interesting insights on the mechanisms of action of DBS and the different role played by the anatomical structures of the subthalamic region. METHODS: Twenty-five patients operated on for bilateral StnDBS were considered. During the surgical procedure, a complete intraoperative neurophysiological study was obtained by means of semimicrorecordings and stimulations. After surgery, an MRI study confirmed the position of the electrodes; MR images were subsequently superimposed onto a stereotactic atlas by using a dedicated workstation. The coordinates relative to the tip of the electrodes and active contacts were then calculated. RESULTS: Most of the electrode tips are located inside the subthalamus or immediately ventrally to it. Of the active contacts used for chronic stimulation, 96.5% are located in a well-defined anatomical region, which includes subthalamus, zona incerta, and FF. CONCLUSIONS: Our findings seem to suggest that other structures beyond the subthalamus itself play a clinical role in symptoms control after DBS for PD.     

Characteristics and distribution of somatosensory evoked potentials in the subthalamic region

OBJECT: The aim of the present study is to evaluate the topographical distribution of somatosensory evoked potentials (SSEPs) in the subthalamic area, including the zona incerta (ZI). Determination of this distribution may help in the correct placement of deep brain stimulation (DBS) leads. METHODS: Intraoperative SSEPs were recorded from contacts of DBS electrodes at 221 sites in 41 patients: three patients with essential tremor and 38 with Parkinson disease who underwent implantation of DBS electrodes for the relief of severe tremor or parkinsonism. RESULTS: Two distinct SSEPs were recorded in the subthalamic area. One was a monophasic positive wave with a mean latency of 15.8 +/- 0.9 msec, which the authors designated subthalamic P16. Using both cephalic and noncephalic references, subthalamic P16 was only recorded in the ventral part of the ZI (mean 6.6 +/- 1.3 mm posterior to the midcommissure point, 4.8 +/- 1.2 mm inferior to the anterior commissure-posterior commissure line, and 9.7 +/- 0.6 mm lateral to the midline). When bipolar recordings were made, the traces showed a phase reversal at the caudal part of the ZI. The second potential is a positive-negative SSEP recorded throughout the entire subthalamic area. The mean latencies of the initial positive peak and the major negative peak were 13.6 +/- 1.1 msec and 16.4 +/- 1.1 msec, respectively. Several small notches were superimposed on the peaks, and their amplitudes were largest at the contact close to the medial lemniscus. CONCLUSIONS: The results indicate that intraoperative SSEPs from DBS electrodes are helpful in refining stereotactic targets in the thalamus and subthalamic areas.     

Correlation between MRI-based stereotactic thalamic deep brain stimulation electrode placement, macroelectrode stimulation and clinical response to tremor control

In this study we compared the position of the electronically active contact of the thalamic (Vim) deep brain stimulation (DBS) electrode to the stereotactic location of its tip. Fifteen patients with either Parkinson's disease (PD) or essential tremor (ET) underwent stereotactic, MRI-based placement of the Medtronic quadripolar DBS electrode. An overall improvement of 69% was achieved in the tremor scores during a period of 1-13 months after implantation of the DBS electrode. Eleven patients with ET showed 70% clinical improvement of tremor, compared to a 58% response observed in the 4 patients with PD. The electrode tip center was 11.2 +/- 1.54 mm lateral to the third ventricular wall, 5.38 +/- 1.02 mm anterior to the posterior commissure and 2.9 +/- 3.57 mm inferior to the level of AC-PC line. The most significant deviation from the planned stereotactic target was observed in the Z-coordinate. In our group of patients, stimulation settings favored the contacts closer to the AC-PC line, correcting the electrode tip position to 0.80 +/- 2.84 mm (p < 0.001) inferior to the level of the AC-PC line. In our experience, thalamic DBS offers a reversible and adjustable 'lesion' to compensate for the anatomic variabilities encountered in the positioning of the DBS electrode tip.     

Brain shift: an error factor during implantation of deep brain stimulation electrodes

OBJECT: The goal of this study was to focus on the tendency of brain shift during stereotactic neurosurgery and the shift's impact on the unilateral and bilateral implantation of electrodes for deep brain stimulation (DBS). METHODS: Eight unilateral and 10 bilateral DBS electrodes at 10 nuclei ventrales intermedii and 18 subthalamic nuclei were implanted in patients at Kaizuka Hospital with the aid of magnetic resonance (MR) imaging-guided and microelectrode-guided methods. Brain shift was assessed as changes in the 3D coordinates of the anterior and posterior commissures (AC and PC) with MR images before and immediately after the implantation surgery. The positions of the implanted electrodes, based on the midcommissural point and AC-PC line, were measured both on x-ray films (virtual position) during surgery and the postoperative MR images (actual position) obtained on the 7th day postoperatively. RESULTS: Contralateral and posterior shift of the AC and PC were the characteristics of unilateral and bilateral procedures, respectively. The authors suggest the following. 1) The first unilateral procedure elicits a unilateral air invasion, resulting in a contralateral brain shift. 2) During the second procedure in the bilateral surgery, the contralateral shift is reset to the midline and, at the same time, the anteroposterior support by the contralateral hemisphere against gravity is lost due to a bilateral air invasion, resulting in a significant posterior (caudal) shift. CONCLUSIONS: To note the tendency of the brain to shift is very important for accurate implantation of a DBS electrode or high frequency thermocoagulation, as well as for the prediction of therapeutic and adverse effects of stereotactic surgery.     

Stimulation of the subthalamic nucleus compared with the globus pallidus internus in patients with Parkinson disease

OBJECT: The authors compared the effects of deep brain stimulation (DBS) in the globus pallidus internus (GPi) with those in the subthalamic nucleus (STN) in patients with Parkinson disease (PD) in whom electrodes had been bilaterally implanted in both targets. METHODS: Eight of 14 patients with advanced PD in whom electrodes had been implanted bilaterally in both the GPi and STN for DBS were selected on the basis of optimal DBS effects and were studied 2 months postsurgery in off- and on-stimulus conditions and after at least 1 month of pharmacological withdrawal. Subcutaneous administration of an apomorphine test dose (0.04 mg/kg) was also performed in both conditions. Compared with the off status, the results showed less reduction in the Unified PD Rating Scale Section III scores during DBS in the GPi (43.1%) than during DBS of the STN (54.5%) or DBS of both the STN and GPi (57.1%). The difference between the effects of DBS in the GPi compared with that in the STN or simultaneous DBS was statistically significant (p < 0.01). In contrast, no statistical difference was found between DBS in the STN and simultaneous DBS in the STN and GPi (p < 0.9). The improvement induced by adding apomorphine administration to DBS was similar in all three stimulus modalities. The abnormal involuntary movements (AIMs) induced by apomorphine were almost abolished by DBS of the GPi, but were not affected by stimulation of the STN. The simultaneous stimulation of STN and GPi produced both antiparkinsonian and anti-AIM effects. CONCLUSIONS: The improvement of parkinsonian symptoms during stimulation of the GPi, STN, and both nuclei simultaneously may indicate a similar DBS mechanism for both nuclei in inducing antiparkinsonian effects, although STN is more effective. The antidyskinetic effects produced only by DBS of the GPi, with or without STN, may indicate different mechanisms for the antidyskinetic and antiparkinsonian activity related to DBS of the GPi or an additional mechanism in the GPi. These findings indicate that implantation of double electrodes for DBS should not be proposed as a routine procedure, but could be considered as a possible subsequent choice if electrode implantation for DBS of the STN does not control AIMs.     

Location of the active contact within the subthalamic nucleus (STN) in the treatment of idiopathic Parkinson's disease

BACKGROUND: Chronic electrical stimulation of the subthalamic nucleus (STN) has been shown to be safe and effective in the treatment of medically refractory idiopathic Parkinson's disease. The clinically most relevant location of stimulation within the physiologically defined STN has not been confirmed. We reviewed the locations of active electrical contacts in 33 patients who underwent simultaneous bilateral STN deep brain stimulator (DBS) implantation. METHODS: The location of the microelectrode-defined dorsal STN border was compared to the location of the center of the active contact(s) employed in achieving optimal clinical results 6 to 18 months postoperatively. Furthermore, the location of this optimal contact was determined with respect to each individual patient's midcommissural point. Bilateral monopolar stimulation was employed in 30 patients using quadripolar DBS electrodes. RESULTS: After a minimum follow-up period of 6 months, the motor subscores (UPDRS Part III) in the postoperative on-stimulation/off-medication state were 64 +/- 18% (mean +/- SD) improved as compared to the preoperative off-medication state (p < 0.01). Additionally, an improvement of 53 +/- 38% was noted when comparing the postoperative on-stimulation/on-medication state to the preoperative on-medication state (p < 0.01). On average, the center of the optimal contact was 13.3 mm lateral, 0.5 mm posterior, 0.1 mm inferior to the mid-commissural point and was 0.1 +/- 2.1 mm dorsal to the physiologically defined dorsal STN border. CONCLUSIONS: While the achieved clinical results are comparable to those published in the literature, it appears that monopolar electrical stimulation at the anterior dorsolateral border of the STN yields optimal clinical results. Further studies are crucial in determining the precise mechanism of various modes of DBS in an effort to maximize clinical outcome.     

Direct effect of subthalamic nucleus stimulation on levodopa-induced peak-dose dyskinesia in patients with Parkinson's disease

We examined the direct effect of deep brain stimulation of the subthalamic nucleus (STN-DBS) on levodopa-induced peak-dose dyskinesia in 45 patients with Parkinson's disease (PD) without reducing the levodopa dosage during the early period after surgery. In 8 patients (18%), the dyskinesia was quickly attenuated by bipolar stimulation in an experimental trial (5 min) with the contacts placed within the area above the STN. In contrast, bipolar stimulation using contacts placed within the STN itself tended to provoke or exacerbate the dyskinesia, indicating that dyskinesia could be inhibited by stimulation of the areas above the STN rather than the STN itself. In an attempt to control the cardinal symptoms of PD and dyskinesia at the same time, we employed bipolar stimulation with a longer interpolar distance as a therapeutic procedure (2 weeks), using contacts within the STN as a cathode and contacts within the area above the STN as an anode. Bilateral STN-DBS significantly attenuated the dyskinesia as evaluated by the dyskinesia severity rating scale (p < 0.05). In 24 patients (53%), almost complete control of the dyskinesia was observed. The contacts used as an anode in these patients were located more dorsally compared to those of the remaining patients, suggesting again that the dyskinesia was inhibited by stimulation of the areas above the STN rather than the STN itself. In the area above the STN, pallidothalamic, pallidosubthalamic and subthalamopallidal fibers are densely distributed. It appears that stimulation of these fibers may cause effects similar to thalamic or pallidal DBS and therefore inhibit peak-dose dyskinesia. Bipolar STN-DBS with contacts placed within the area above the STN as an anode appears to represent a useful option for controlling both the cardinal symptoms of PD and peak-dose dyskinesia at the same time.     

Postmortem analysis following 71 months of deep brain stimulation of the subthalamic nucleus for Parkinson disease

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) is a clinically effective neurosurgical treatment for Parkinson disease. Tissue reaction to chronic DBS therapy and the definitive location of active stimulation contacts are best studied on a postmortem basis in patients who have undergone DBS. The authors report the postmortem analysis of STN DBS following 5 years and 11 months of effective chronic stimulation including the histologically verified location of the active contacts associated with bilateral implants. They also describe tissue response to intraoperative test passes with recording microelectrodes and stimulating semimacroelectrodes. The results indicated that 1) the neural tissue surrounding active and nonactive contacts responds similarly, with a thin glial capsule and foreign-body giant cell reaction surrounding the leads as well as piloid gliosis, hemosiderin-laden macrophages, scattered lymphocytes, and Rosenthal fibers; 2) there was evidence of separate tracts in the adjacent tissue for intraoperative microelectrode and semimacroelectrode passes together with reactive gliosis, microcystic degeneration, and scattered hemosiderin deposition; and 3) the active contacts used for approximately 6 years of effective bilateral DBS therapy lie in the zona incerta, just dorsal to the rostral STN. To the authors' knowledge, the period of STN DBS therapy herein described for Parkinson disease and subjected to postmortem analysis is the longest to date.     

Neural Activity of the Subthalamic Nucleus in Parkinson's Disease Patients

Summary  The neural activity pattern of the subthalmic nucleus (STN) was investigated in five patients with Parkinson's disease who were scheduled for electrode implantation for chronic stimulation of the STN.  The initial target was placed 8 mm or 10 mm lateral to the midline, 3 mm to 4 mm posterior to the midcommissural point, and 5 mm to 6 mm below the intercommissural (AC-PC) line. The STN was identified by semi-microelectrode recordings with a trajectory moving laterally in 2-mm steps. The amplitudes of multi-unit activities were relatively low at depths from 8 mm to 5 mm above and from 1 mm to 4 mm below the target, while those 4 mm to 0 mm above the target were significantly higher than at the other sites (ANOVA, Fisher's test, p<0.05), with the highest amplitude at 2 mm above the target (91.0±23.3μv, n=15). In the mediolateral direction, amplitudes were relatively higher in the lateral portion, and amplitudes at 14 mm lateral to the midline were significantly higher than at the other sites (ANOVA, Fisher's test, p<0.05). The target for chronic electrical stimulation was determined to be at the midpoint of the hyperactive STN, i.e., 12 mm lateral to the midline in three patients and 13 mm lateral in two patients. Movement-related neural activity was observed at 5 sites, i.e., 3 sites responded to passive movement of the contralateral wrist and 2 sites to passive knee and/or ankle movement.  In conclusion, our data show that the lateral part of the STN is hyperactive in PD, and recordings of neural activities contributed greatly to identifying the STN and determining the target for chronic stimulation within it.     

Multiple sequential image-fusion and direct MRI localisation of the subthalamic nucleus for deep brain stimulation

AIM: Deep brain stimulation (DBS) is the treatment of choice for advanced Parkinson's disease. The target co-ordinates are traditionally calculated in relation to the intercommissural distance. Anterior (AC) and posterior commissures (PC) may be visualised by the means of ventriculography, CT or MRI. METHODS: We have studied the efficacy of direct visualisation of the subthalamic-red nucleus complex on MRI, the advantage of fusion of stereotactic CT and MR images (Multiple Sequences Image Fusion - MuSIF). These methods are combined with double check of indirect calculation of the target co-ordinates based on AC-PC line, as well as the corrispondence to the stereotactic electronic atlas. RESULTS: Subthalamic nucleus (STN) was well recognisable in fused images in all 22 sides. At 3 months from surgery it was possible to reduce 76% of L-dopa equivalent daily dose. Dyskine-sias reduced to 50% and motor fluctuation up to 45%. CONCLUSION: In our experience MuSIF offers very high rate of accuracy in calculation of target co-ordinates. Direct visualisation of STN in MR and MuSIF are reliable and facilitate the accuracy of identification of target co-ordinates. Intraoperative neurophysiological recording increases the accuracy of microelectrode position.     

Modeling parkinsonian circuitry and the DBS electrode. II. Evaluation of a computer simulation model of the basal ganglia with and without subthalamic nucleus stimulation

Treatment with deep brain stimulation (DBS) for Parkinson's disease (PD) has become routine over the past decade, particularly using the subthalamic nucleus (STN) as a target and utilizing microelectrode recordings to ensure accurate placement of the stimulating electrodes. The clinical changes seen with DBS in the STN for PD are consistently beneficial, but there continues to be only marginal understanding of the mechanisms by which DBS achieves these results. Using an analytical model of the typical DBS 4-contact electrode and software developed to simulate individual neurons and neural circuitry of the basal ganglia we compare the results of the model to those of data obtained during DBS surgery of the STN. Firing rate, interspike intervals and regularity analyses were performed on the simulated data and compared to results in the literature.     

Bilateral stimulation of the subthalamic nucleus in patients with Parkinson disease: a study of efficacy and safety

OBJECT: Palliative neurosurgery has reemerged as a valid therapy for patients with advanced Parkinson disease (PD) that is complicated by severe motor fluctuations. Despite great enthusiasm for long-term deep brain stimulation (DBS) of the subthalamic nucleus (STN), existing reports on this treatment are limited. The present study was designed to investigate the safety and efficacy of bilateral stimulation of the STN for the treatment of PD. METHODS: In 12 patients with severe PD, electrodes were stereotactically implanted into the STN with the assistance of electrophysiological conformation of the target location. All patients were evaluated preoperatively during both medication-off and -on conditions, as well as postoperatively at 3, 6, and 12 months during medication-on and -off states and stimulation-on and -off conditions. Tests included assessments based on the Unified Parkinson's Disease Rating Scale (UPDRS) and timed motor tests. The stimulation effect was significant in patients who were in the medication-off state, resulting in a 47% improvement in the UPDRS Part III (Motor Examination) score at 12 months, compared with preoperative status. The benefit was stable for the duration of the follow-up period. Stimulation produced no additional benefit during the medication-on state, however, when compared with patient preoperative status. Significant improvements were made in reducing dyskinesias, fluctuations, and duration of off periods. CONCLUSIONS: This study demonstrates that DBS of the STN is an effective treatment for patients with advanced, medication-refractory PD. Deep brain stimulation of the STN produced robust improvements in motor performance in these severely disabled patients while they were in the medication-off state. Serious adverse events were common in this cohort; however, only two patients suffered permanent sequelae.     

Combined pallidal and subthalamic nucleus stimulation in sporadic dystonia-parkinsonism

Multifocal deep brain stimulation (DBS) is a new technique that has been introduced recently. A 39-year-old man with dystonia-parkinsonism underwent the simultaneous implantation of subthalamic nucleus (STN) and globus pallidus internus (GPi) DBS electrodes. While bilateral STN DBS controlled the parkinsonian symptoms well and allowed for a reduction in levodopa, the improvement of dystonia was only temporary. Additional GPi DBS also alleviated dystonic symptoms. Formal assessment at the 1-year follow-up showed that both the parkinsonian symptoms and the dystonia were markedly improved via continuous bilateral combined STN and GPi stimulation. Sustained benefit was achieved at 3 years postoperatively.     

Microelectrode recording revealing a somatotopic body map in the subthalamic nucleus in humans with Parkinson disease

OBJECT: The subthalamic nucleus (STN) is a key structure for motor control through the basal ganglia. The aim of this study was to show that the STN in patients with Parkinson disease (PD) has a somatotopic organization similar to that in nonhuman primates. METHODS: A functional map of the STN was obtained using electrophysiological microrecording during placement of deep brain stimulation (DBS) electrodes in patients with PD. Magnetic resonance imaging was combined with ventriculography and intraoperative x-ray film to assess the position of the electrodes and the STN units, which were activated by limb movements to map the sensorimotor region of the STN. Each activated cell was located relative to the anterior commissure-posterior commissure line. Three-dimensional coordinates of the cells were analyzed statistically to determine whether those cells activated by movements of the arm and leg were segregated spatially. Three hundred seventy-nine microelectrode tracks were created during placement of 71 DBS electrodes in 44 consecutive patients. Somatosensory driving was found in 288 tracks. The authors identified and localized 1213 movement-related cells and recorded responses from 29 orofacial cells, 480 arm-related cells, 558 leg-related cells, and 146 cells responsive to both arm and leg movements. Leg-related cells were localized in medial (p < 0.0001) and ventral (p < 0.0004) positions and tended to be situated anteriorly (p = 0.063) relative to arm-related cells. CONCLUSIONS: Evidence of somatotopic organization in the STN in patients with PD supports the current theory of highly segregated loops integrating cortex-basal ganglia connections. These loops are preserved in chronic degenerative diseases such as PD, but may subserve a distorted body map. This finding also supports the relevance of microelectrode mapping in the optimal placement of DBS electrodes along the subthalamic homunculus.     

Subthalamic nucleus deep brain stimulation for Parkinson's disease: magnetic resonance imaging targeting using visible anatomical landmarks

BACKGROUND: The aim of the present study was to validate a magnetic resonance imaging (MRI) visual procedure to target the subthalamic nucleus (STN) based on surrounding anatomical landmarks. METHODS: 31 consecutive bilaterally implanted parkinsonian patients were included in this study. After identification of the anterior commissure (AC), posterior commissure (PC) and midcommissural point on a three-dimensional T1-weighted sequence, inversion recovery (IR) T2-weighted coronal slices were performed orthogonal to the AC-PC line. On the slice showing the anterior pole of the red nucleus (RN), the target was placed in the inferolateral portion of the subthalamic zone, limited superiorly by the thalamus, laterally by the internal capsule, inferiorly by the substantia nigra and medially by the midline. The distribution of the targets was analyzed in the AC-PC referential. RESULTS: The mean target coordinates were as follows: anteroposterior (AP) = -2.54 mm (+/-1.37 mm), lateral (LAT) = 12.03 mm (+/-0.91 mm) and vertical (VERT) = -6.10 mm (+/-1.52 mm) for the right side, and AP = -2.65 mm (+/-1.36 mm), LAT = -11.97 mm (+/-1.30 mm) and VERT = -5.89 mm (+/-1.52 mm) for the left side. They projected in the inferior portion of the STN on the Schaltenbrand and Wahren atlas [Stuttgart, Thieme, 1977]. CONCLUSION: Identification of the anterior pole of the RN and the subthalamic zone on coronal IR T2-weighted MRI performed orthogonal to the AC-PC line provides a precise visual procedure to target the STN.