Effective Electrode Contact Research Articles

Brain connectivity markers for the identification of effective contacts in subthalamic nucleus deep brain stimulation.

The clinical benefit of deep brain stimulation (DBS) for Parkinson's disease (PD) is relevant to the tracts adjacent to the stimulation site, but it remains unclear what connectivity pattern is associated with effective DBS. The aim of this study was to identify clinically effective electrode contacts on the basis of brain connectivity markers derived from diffusion tensor tractography. We reviewed 77 PD patients who underwent bilateral subthalamic nucleus DBS surgery. The patients were assigned into the training (n = 58) and validation (n = 19) groups. According to the therapeutic window size, all contacts were classified into effective and ineffective groups. The whole‐brain connectivity of each contact's volume of tissue activated was estimated using tractography with preoperative diffusion tensor data. Extracted connectivity features were put into an all‐relevant feature selection procedure within cross‐validation loops, to identify features with significant discriminative power for contact classification. A total of 616 contacts on 154 DBS leads were discriminated, with 388 and 228 contacts being classified as effective and ineffective ones, respectively. After the feature selection, the connectivity of contacts with the thalamus, pallidum, hippocampus, primary motor area, supplementary motor area and superior frontal gyrus was identified to significantly contribute to contact classification. Based on these relevant features, the random forest model constructed from the training group achieved an accuracy of 84.9% in the validation group, to discriminate effective contacts from the ineffective. Our findings advanced the understanding of the specific brain connectivity patterns associated with clinical effective electrode contacts, which potentially guided postoperative DBS programming.

White matter tracts involved by deep brain stimulation of the subthalamic nucleus in Parkinson’s disease: a connectivity study based on preoperative diffusion tensor imaging tractography

Purpose: To depict the specific brain networks that are modulated by deep brain stimulation (DBS) of the subthalamic nucleus (STN) in Parkinson’s disease (PD), using diffusion tensor imaging-based fibre tractography (DTI-FT).Materials and methods: Nine patients who received bilateral STN-DBS for PD were included. Electrodes were localized by co-registering preoperative magnetic resonance imaging and postoperative computed tomography. The volume of tissue activated (VTA) was estimated as an isotropic, spherical electric field distribution centred at each effective electrode contact’s centroid coordinates, taking into account individual stimulation parameters (i.e. voltage, impedance). Brain connectivity analysis was undertaken using a deterministic DTI-FT method, seeded from a single region of interest corresponding to the VTA. The labelling of the reconstructed white matter fibre tracts relied on their path and (sub)cortical termination territories.Results: Six months after surgery, we observed a statistically significant reduction in both the Unified Parkinson Disease Rating Scale part III and L-dopa equivalent daily dose. Areas consistently connected to the VTA included the brainstem (100%), cerebellum (94%), dorsal (i.e. supplementary motor area) and lateral premotor cortex (94%), and primary motor cortex (72%). An involvement of the hyperdirect pathway (HDP) connecting the STN and the (pre)motor cortex was demonstrated.Conclusions: The connectivity patterns observed in this study suggest that the therapeutic effects of STN-DBS are mediated through the modulation of distributed, large-scale motor networks. Specifically, the depiction of projection neurons connecting the stimulated area/STN to the (pre)motor cortex, reinforce the growing evidence that the HDP might be a potential therapeutic target in PD. If further replicated, these findings could raise the possibility that DTI-FT reconstruction of the HDP may critically improve DBS targeting and stimulation parameters selection, through the development of programming tools that incorporate VTA modelling and patient-specific DTI-FT data.

Effect of Pressure on Skin-Electrode Impedance in Wearable Biomedical Measurement Devices

Objective: This paper investigates the effect of applied pressure on the skin-electrode impedance. Applied pressure, which affects the skin-electrode impedance, can fluctuate in many acquisition setups, particularly in wearable devices. The skin-electrode impedance, in turn, impacts the quality of the recorded signal in biomedical monitoring devices. Methods: Three types of electrodes were examined: Ag/AgCl electrodes, conductive textile electrodes, and dry electrodes with surface microfeatures (Orbital Research Inc.). Impedance measurements were conducted as pressure was repeatedly applied ( $P = 4$ kPa) and removed ( $P = 0$ kPa) over several trials. A Cole–Cole impedance model was utilized to model the skin-electrode interface. Significance and Results: Results demonstrated large decreases in the skin-electrode impedance of dry electrodes (conductive textile and orbital electrodes), especially with the initial application of the pressure. Model parameters also proved to be highly dependent on the level of pressure in dry electrodes but less dependent and more stable in wet electrodes. Decreases in skin-electrode impedance associated with applied pressure were thought to be caused by an increased effective electrode contact area. Changes in skin-electrode impedance were irreversible, lasting even after the applied pressure was released. Differences skin-electrode impedance associated with changes in applied pressure, decreased as the number of trials increased. Conclusion: Applied pressure has larger effect on dry electrodes than wet electrodes. Wearable devices that employ dry electrodes may have poorer biomedical signal quality when initially donned; however, the advantage of wet electrodes with their lower sensitivity to applied pressure is diminished in long-term monitoring applications.

Assessment of a method to determine deep brain stimulation targets using deterministic tractography in a navigation system.

Recent advances in imaging permit radiologic identification of target structures for deep brain stimulation (DBS) for movement disorders. However, these methods cannot detect the internal subdivision and thus cannot determine the appropriate DBS target located within those subdivisions. The aim of this study is to provide a straightforward method to obtain an optimized target (OT) within DBS target nuclei using a widely available navigation system. We used T1- and T2-weighted images, fluid-attenuated inversion recovery (FLAIR) sequence, and diffusion tensor imaging (DTI) of nine patients operated for DBS in our center. Using the StealthViz® software, we segmented the targeted deep structures (subcortical targets) and the anatomically identifiable areas to which these target nuclei were connected (projection areas). We generated fiber tracts from the projection areas. By identifying their intersections with the subcortical targets, we obtained an OT within the DBS target nuclei. We computed the distances from the clinically effective electrode contacts (CEEC) to the OT obtained by our method and the targets provided by the atlas. These distances were compared using a Wilcoxon signed-rank test, with p < 0.05 considered statistically significant. We were able to identify OT coincident with the motor part of the subthalamic nucleus and the ventral intermediate nucleus. We clinically tested the results and found that the CEEC were significantly more closely related to the OT than with the targets obtained by the atlas. Our present results show that this novel method permits optimization of the stimulation site within the internal subdivisions of target nuclei for DBS.

Characterizing effects of subthalamic nucleus deep brain stimulation on methamphetamine-induced circling behavior in hemi-Parkinsonian rats.

The unilateral 6-hydroxydopamine (6-OHDA) lesioned rat model is frequently used to study the effects of subthalamic nucleus (STN) deep brain stimulation (DBS) for the treatment of Parkinson's disease. However, systematic knowledge of the effects of DBS parameters on behavior in this animal model is lacking. The goal of this study was to characterize the effects of DBS on methamphetamine-induced circling in the unilateral 6-OHDA lesioned rat. DBS parameters tested include stimulation amplitude, stimulation frequency, methamphetamine dose, stimulation polarity, and anatomical location of the electrode. When an appropriate stimulation amplitude and dose of methamphetamine were applied, high-frequency stimulation (> 130 Hz), but not low frequency stimulation (< 10 Hz), reversed the bias in ipsilateral circling without inhibiting movement. This characteristic frequency tuning profile was only generated when at least one electrode used during bipolar stimulation was located within the STN. No difference was found between bipolar stimulation and monopolar stimulation when the most effective electrode contact was selected, indicating that monopolar stimulation could be used in future experiments. Methamphetamine-induced circling is a simple, reliable, and sensitive behavioral test and holds potential for high-throughput study of the effects of STN DBS in unilaterally lesioned rats.

Relationship of Stimulation Site Location within the Subthalamic Nucleus Region to Clinical Effects on Parkinsonian Symptoms

Objective: To determine the relationship of the stimulation site in the subthalamic region to the clinical effects on parkinsonian symptoms, the monopolar stimulation of 4 electrode contacts and the resulting effects on parkinsonian symptoms were evaluated. Methods: Seventeen consecutive patients (3 males and 14 females) were enrolled in the study. The patients were evaluated while in a nonmedicated state, and 10–20 min after switching on the pulse generator the effects of stimulation were assessed using separate-subset Unified Parkinson’s Disease Rating Scale scores. Results: The relationship between the site stimulated and the percent improvement was analyzed using polynomial regression. Rigidity (p = 0.0004, R² = 0.15), akinesia (p = 0.02, R² = 0.07) and total score (p = 0.009, R² = 0.089) well fit to second-order polynomial regression and showed the greatest improvement after stimulation at 0–1 mm below the horizontal anterior-posterior commissure (AC-PC) plane. Tremor (p = 0.24, R² = 0.18) and gait (p = 0.36, R² = 0.001) had a weak relation to the site stimulated, but stimulation at the sites 0–1 mm below the AC-PC plane also produced greater improvement than stimulation at more ventral or dorsal sites. The percent improvement of the posture (p = 0.92, R² = 0.002) had no relation to the site stimulated. The dorsal border of the subthalamic nucleus was located 0.6 ± 1.2 mm (n = 27) below the AC-PC plane and the most effective electrode contact 1.2 ± 1.3 mm (n = 27) below it. Conclusions: Stimulation around the dorsal border of the subthalamic nucleus, close to the AC-PC plane, produces greater improvement of parkinsonian symptoms than stimulation at more ventral or dorsal sites.

Deep brain stimulation of the subthalamic nucleus in Parkinson’s disease: evaluation of active electrode contacts

Background: The subthalamic nucleus is the preferred target for deep brain stimulation in patients with advanced Parkinson’s disease. The site of permanent stimulation is the subject of ongoing debate, as...