Electrode Placement Research Articles

Deep Brain Stimulation (DBS) in Treatment-Resistant Depression (TRD): Hope and Concern.

In this chapter, we explore the historical evolution, current applications, and future directions of Deep Brain Stimulation (DBS) for Treatment-Resistant Depression (TRD). We begin by highlighting the early efforts of neurologists and neurosurgeons who laid the foundations for today's DBS techniques, moving from controversial lobotomies to the precision of stereotactic surgery. We focus on the advent of DBS, emphasizing its emergence as a significant breakthrough for movement disorders and its extension to psychiatric conditions, including TRD. We provide an overview of the neural networks implicated in depression, detailing the rationale for the choice of common DBS targets. We also cover the technical aspects of DBS, from electrode placement to programming and parameter selection. We then critically review the evidence from clinical trials and open-label studies, acknowledging the mixed outcomes and the challenges posed by placebo effects and trial design. Safety and ethical considerations are also discussed. Finally, we explore innovative directions for DBS research, including the potential of closed-loop systems, dual stimulation strategies, and noninvasive alternatives like ultrasound neuromodulation. In the last section, we outline recommendations for future DBS studies, including the use of alternative designs for placebo control, the collection of neural and behavioral recordings, and the application of machine-learning approaches.

Incidence of complications associated with deep brain stimulation surgery in patients with Parkinson's disease: An 8-year retrospective study.

Various complications occur in patients undergoing deep brain stimulation (DBS) surgery. The objective of this study was to determine the incidence of complications in patients with Parkinson's disease who underwent DBS surgery and identify the risk factors, especially anesthetic factors. A retrospective cohort study was performed between May 2015 and December 2022. Based on a review of medical charts, patients aged 18 years or older who underwent DBS surgery at a tertiary neurological center in Thailand were recruited. Univariate analysis using the Chi-square test or Fisher's exact test was performed to compare patients with and without complications. Multivariate logistic regression analysis was performed to identify the predictive factors for complications. The study included 46 patients. The most common complication during DBS electrode placement was hypertension (30/46, 65.2%), and 19 patients (41.3%) who developed hypertension did not receive antihypertensive treatment. The most common complication during battery placement was clinical hypotension (14/46, 30.4%). The most common postoperative complication was delirium (6/46, 13.0%). In the multivariate analysis, no significant independent risk factors for overall complications after DBS surgery were identified. Hypertension during DBS electrode insertion was the most common perioperative complication. Hemodynamic instability is preventable and manageable, and vigilant and prompt treatment should be provided during DBS surgery.

Facial nerve electrical motor evoked potential in cerebellopontine angle tumors for its anatomical and functional preservation.

Among the technical measures to preserve facial nerve (FN) function, intraoperative neuromonitoring has become mandatory and is constantly being scrutinized. Hence, to determine the efficacy of FN motor evoked potentials (FNMEPs) in predicting long-term motor FN function following cerebellopontine angle (CPA) tumor surgery, an analysis of cases was done. In 37 patients who underwent CPA surgery, FNMEPs through corkscrew electrodes positioned at C5-C6 and C6-C5 (C is the central line of the brain as per 10-20 EEG electrode placement) were used to deliver short train stimuli and recorded from the orbicularis oculi, oris, and mentalis muscles. In 58 patients, triggered electromyography (EMG) was able to identify the FN during resection of tumor, but 8 out of these (4.64%) patients developed new facial weakness, whereas 3 out of 38 (1.11%) patients who had intact FN function MEP (decrement of FN target muscles - CMAPs amplitude peak to peak >50-60%), developed new facial weakness (House and Brackmann grade II to III). The FNMEP has significant superiority over triggered EMG when tumor is giant and envelops the FN.

Effective connectivity relates seizure outcome to electrode placement in responsive neurostimulation.

Responsive neurostimulation is a closed-loop neuromodulation therapy for drug resistant focal epilepsy. Responsive neurostimulation electrodes are placed near ictal onset zones so as to enable detection of epileptiform activity and deliver electrical stimulation. There is no standard approach for determining the optimal placement of responsive neurostimulation electrodes. Clinicians make this determination based on presurgical tests, such as MRI, EEG, magnetoencephalography, ictal single-photon emission computed tomography and intracranial EEG. Currently functional connectivity measures are not being used in determining the placement of responsive neurostimulation electrodes. Cortico-cortical evoked potentials are a measure of effective functional connectivity. Cortico-cortical evoked potentials are generated by direct single-pulse electrical stimulation and can be used to investigate cortico-cortical connections in vivo. We hypothesized that the presence of high amplitude cortico-cortical evoked potentials, recorded during intracranial EEG monitoring, near the eventual responsive neurostimulation contact sites is predictive of better outcomes from its therapy. We retrospectively reviewed 12 patients in whom cortico-cortical evoked potentials were obtained during stereoelectroencephalography evaluation and subsequently underwent responsive neurostimulation therapy. We studied the relationship between cortico-cortical evoked potentials, the eventual responsive neurostimulation electrode locations and seizure reduction. Directional connectivity indicated by cortico-cortical evoked potentials can categorize stereoelectroencephalography electrodes as either receiver nodes/in-degree (an area of greater inward connectivity) or projection nodes/out-degree (greater outward connectivity). The follow-up period for seizure reduction ranged from 1.3-4.8 years (median 2.7) after responsive neurostimulation therapy started. Stereoelectroencephalography electrodes closest to the eventual responsive neurostimulation contact site tended to show larger in-degree cortico-cortical evoked potentials, especially for the early latency cortico-cortical evoked potentials period (10-60 ms period) in six out of 12 patients. Stereoelectroencephalography electrodes closest to the responsive neurostimulation contacts (≤5 mm) also had greater significant out-degree in the early cortico-cortical evoked potentials latency period than those further away (≥10 mm) (P < 0.05). Additionally, significant correlation was noted between in-degree cortico-cortical evoked potentials and greater seizure reduction with responsive neurostimulation therapy at its most effective period (P < 0.05). These findings suggest that functional connectivity determined by cortico-cortical evoked potentials may provide additional information that could help guide the optimal placement of responsive neurostimulation electrodes.

Efficacy of Transcranial Direct Current Stimulation on Pain Level and Disability of Patients with Fibromyalgia: A Systematic Review of Randomized Controlled Trials with Parallel-Group Design.

Transcranial direct current stimulation (tDCS) has been increasingly applied in fibromyalgia (FM) to reduce pain and fatigue. While results are promising, observed effects are variable, and there are questions about optimal stimulation parameters such as target region (e.g., motor vs. prefrontal cortices). This systematic review aimed to provide the latest update on published randomized controlled trials with a parallel-group design to examine the specific effects of active tDCS in reducing pain and disability in FM patients. Using the PRISMA approach, a literature search identified 14 randomized controlled trials investigating the effects of tDCS on pain and fatigue in patients with FM. Assessment of biases shows an overall low-to-moderate risk of bias. tDCS was found effective in all included studies conducted in patients with FM, except one study, in which the improving effects of tDCS were due to placebo. We recommended tDCS over the motor and prefrontal cortices as "effective" and "probably effective" respectively, and also safe for reducing pain perception and fatigue in patients with FM, according to evidence-based guidelines. Stimulation polarity was anodal in all studies, and one single-session study also examined cathodal polarity. The stimulation intensity ranged from 1-mA (7.14% of studies) to 1.5-mA (7.14% of studies) and 2-mA (85.7% of studies). In all of the included studies, a significant improvement in at least one outcome variable (pain or fatigue reduction) was observed. Moreover, 92.8% (13 of 14) applied multi-session tDCS protocols in FM treatment and reported significant improvement in their outcome variables. While tDCS is therapeutically effective for FM, titration studies that systematically evaluate different stimulation intensities, durations, and electrode placement are needed.

Electrophysiological recording in deep brain stimulation: Current status

Deep brain stimulation (DBS) is a surgical treatment critical for alleviating symptoms of Parkinson's disease (PD), especially when medication fails to manage motor dysfunctions effectively. The accuracy of electrode placement in the subthalamic nucleus (STN) is critical for the procedure's success. The long-standing debate between electrophysiological recording (MER) and imaging-based targeting remains at the forefront of neurosurgical discussions. MER has traditionally been used to enhance the precision of DBS targeting, indicated by changes in local field potentials (LFPs), which correlate with Parkinsonian motor symptoms such as rigidity, bradykinesia, and tremor. However, the necessity of MER has been questioned due to advances in imaging techniques and the potential risks associated with the practice, including hemorrhage and cognitive decline post-surgery. A critical appraisal of the literature reveals mixed opinions, with recent meta-analyses showing no significant increase in hemorrhage risks with MER but demonstrating a modest increase in adverse cognitive outcomes using multiple electrodes. Despite improved imaging modalities enabling more accurate radiological targeting, MER remains a favored technique among surgeons for its direct feedback on electrode placement. Additionally, the aspect of conducting surgery under awake conditions versus general anesthesia is reviewed, considering the anxiety and discomfort associated with awake surgery against the limitations of performing electrophysiological recordings under general anesthesia. The current consensus underscores the importance of accurate electrode placement, achievable through a combination of MER, test stimulation, and intraoperative imaging, while also acknowledging the growing confidence in image-guided procedures performed under general anesthesia. This review highlights the need for individualized approaches considering patient-specific risks and the evolving landscape of DBS surgery.

Day one postoperative MRI findings following electrode placement for deep brain stimulation: analysis of a large case series.

This study sought to characterize postoperative day one MRI findings in deep brain stimulation (DBS) patients. DBS patients were identified by CPT and had their reviewed by a trained neuroradiologist and neurosurgeon blinded to MR sequence and patient information. The radiographic abnormalities of interest were track microhemorrhage, pneumocephalus, hematomas, and edema, and the occurrence of these findings in compare the detection of these complications between T1/T2 gradient-echo (GRE) and T1/T2 fluid-attenuated inversion recovery (FLAIR) magnetic resonance (MR) sequences was compared. The presence, size, and association of susceptibility artifact with other radiographic abnormalities was also described. Lastly, the association of multiple microelectrode cannula passes with each radiographic finding was evaluated. Ad-hoc investigation evaluated hemisphere-specific associations. Multiple logistic regression with Bonferroni correction (corrected p = 0.006) was used for all analysis. Out of 198 DBS patients reviewed, 115 (58%) patients showed entry microhemorrhage; 77 (39%) track microhemorrhage; 44 (22%) edema; 69 (35%) pneumocephalus; and 12 (6%) intracranial hematoma. T2 GRE was better for detecting microhemorrhage (OR = 14.82, p < 0.0001 for entry site and OR = 4.03, p < 0.0001 for track) and pneumocephalus (OR = 11.86, p < 0.0001), while T2 FLAIR was better at detecting edema (OR = 123.6, p < 0.0001). The relatively common findings of microhemorrhage and edema were best visualized by T2 GRE and T2 FLAIR sequences, respectively. More passes intraoperatively was associated with detection of ipsilateral track microhemorrhage (OR = 7.151, p < 0.0001 left; OR = 8.953, p < 0.0001 right). Susceptibility artifact surrounding electrodes possibly interfered with further detection of ipsilateral edema (OR = 4.323, p = 0.0025 left hemisphere only). Day one postoperative magnetic resonance imaging (MRI) for DBS patients can be used to detect numerous radiographic abnormalities not identifiable on a computed tomographic (CT) scan. For this cohort, multiple stimulating cannula passes intraoperatively was associated with increased microhemorrhage along the electrode track. Further studies should be performed to evaluate the clinical relevance of these observations.

Brain stimulation targets for chronic pain: Insights from meta-analysis, functional connectivity and literature review

Noninvasive brain stimulation (NIBS) techniques have demonstrated their potential for chronic pain management, yet their efficacy exhibits variability across studies. Refining stimulation targets and exploring additional targets offer a possible solution to this challenge. This study aimed to identify potential brain surface targets for NIBS in treating chronic pain disorders by integrating literature review, neuroimaging meta-analysis, and functional connectivity analysis on 90 chronic low back pain patients. Our results showed that the primary motor cortex (M1) (C3/C4, 10–20 EEG system) and prefrontal cortex (F3/F4/Fz) were the most used brain stimulation targets for chronic pain treatment according to the literature review. The bilateral precentral gyrus (M1), supplementary motor area, Rolandic operculum, and temporoparietal junction, were all identified as common potential NIBS targets through both a meta-analysis sourced from Neurosynth and functional connectivity analysis. This study presents a comprehensive summary of the current literature and refines the existing NIBS targets through a combination of imaging meta-analysis and functional connectivity analysis for chronic pain conditions. The derived coordinates (with integration of the international electroencephalography (EEG) 10/20 electrode placement system) within the above brain regions may further facilitate the localization of these targets for NIBS application. Our findings may have the potential to expand NIBS target selection beyond current clinical trials and improve chronic pain treatment.

Subthalamic nucleus neuronal activity entropy in the effective stimulation area in patients with Parkinson’s disease

One of the most successful and promising treatments for Parkinson’s disease today is deep brain stimulation (DBS). Accurate localization of the stimulation area is critical for the outcome of surgical DBS electrode implantation in the subthalamic nucleus (STN). To achieve this, microelectrode recording is used during surgery to precisely locate the STN borders [1], while test stimulations with a macroelectrode are widely employed to enhance DBS electrode placement accuracy. Thus, through testing multiple trajectories, the most clinically effective one can be selected. However, a comprehensive and reliable description of the specific single neuron activity associated with successful DBS electrode implantation is currently lacking. A study was conducted using microelectrode recordings (MER) of single neuron activity in the STN of 21 Parkinson’s disease patients (UPDRS III off/on=46.9/12.8) to identify the neuronal activity features associated with the most favorable clinical outcome of test stimulation. A comparative analysis of 29 activity parameters, such as firing rate, oscillatory activity intensity in different frequency ranges (Oscores), coefficient of variation, burst, pause index, among others [2], was conducted for 618 identified neurons. In addition, the approach of computing the entropy of the change in interspike intervals (ISI) of the pulse sequence [3] and the process of identifying patterns of neural activity using hierarchical clustering [4] were implemented. A comparative analysis of single neuron activity indicated notable (p 0.05) variations between disregarded and selected paths for the ultimate implantation of DBS electrode, solely relying on entropy parameters. Trajectories that delivered optimal test stimulation outcomes demonstrated reduced entropy of interspike intervals. Only the patterns of neuronal activity characterized by extended periods of steady firing and brief pauses, referred to as tonic and pause activity, respectively, were found to contribute to the difference in entropy between trajectories. In contrast, there were no statistically significant differences detected in entropy values associated with neurons demonstrating burst activity. Furthermore, we observed a positive and significant correlation between entropy values and the degree of improvement in disease presentation before and after administration of medication. A comparative analysis was conducted on the activity of single neurons along different trajectories with varied test stimulation responses. The results showed a weak effectiveness of linear parameters in determining the optimal electrode insertion path for improved clinical outcomes. However, the use of non-linear activity parameters, specifically entropy, in single neurons effectively differentiated trajectories with significant versus absent/insignificant test stimulation results. Furthermore, the significance of entropy in establishing the basal ganglia functions and describing information transfer processes in movement control is emphasized by interpreting this parameter as a measure of uncertainty or unpredictability of the information system in relation to the findings of other studies [5].

Effects of electrode placement on symptoms, memory, and sustainment of results after electroconvulsive therapy- A comparative study

ABSTRACT Background: The memory-related side-effects rank among the strongest reasons for hostility against Modified Electroconvulsive Therapy (MECT). Most of the studies comparing the Unilateral v/s Bilateral Electrode placements on memory have been conducted on patients with depression while very few studies have been conducted on patients with psychosis in the Indian population. Aim: To compare the effects of right unilateral (RU/L) and bilateral (B/L) MECT on the severity of symptoms as well as memory in patients with psychosis after the fourth session and two weeks after the final session of the MECT. Materials and Methods: One hundred patients having a psychotic illness were randomized into either RU/L or B/L group. Comprehensive psychopathological rating scale (CPRS), clinical global impressions scale (CGI-S), and PGI-memory scale were applied before starting of MECT, after four sessions of MECT and two weeks after the last session of ECT. Results: The results show similar symptomatic improvement in patients receiving RU/L and B/L MECT and the results persisted beyond the therapy sessions. But, in the case of RU/L-MECT group, the deterioration in memory was less as compared to the B/L-MECT group. Both groups had no significant difference in psychopathology and its severity (CPRS and CGI). Both groups were significantly different in memory side effects after the fourth session and two weeks after the last session. Both groups showed a consistent downward trend in psychopathology and its severity. The consistent fall in the total PGI scores remained even after two weeks of the final session in the B/L group (total of six points as compared to baseline) while it came to baseline levels in the RU/L group. Both groups differed significantly in total PGI scores after the fourth session and two weeks after the final session. Conclusion: This study points toward a favorable outcome in the case of therapeutic response with MECT without any significant difference between both types of electrode placements and even after stopping MECT, the improvement appears to be stable over time. Although, there was a side-effect of memory impairment, it appears to be for a shorter duration and it improves with time. The side-effect profile of RU/L electrode placement is lower as compared to bilateral placement. In the post-MECT period, the patients receiving MECT with RU/L electrode placement showed better improvement in memory functions.

Good moments to stimulate the brain – A randomized controlled double-blinded study on anodal transcranial direct current stimulation of the ventromedial prefrontal cortex on two different time points in a two-day fear conditioning paradigm

It is assumed that extinction learning is a suitable model for understanding the mechanisms underlying exposure therapy. Furthermore, there is evidence that non-invasive brain stimulation (NIBS) can elevate extinction learning by enhancing frontal brain activity and therefore NIBS can augment symptom reduction during exposure therapy in phobias. But, the underlying processes are still not well established. Open questions arise from NIBS time points and electrode placement, among others. Therefore, we investigated in a 2-day fear conditioning experiment, whether anodal transcranial direct current stimulation (tDCS) of the ventromedial prefrontal cortex (vmPFC) modulates either fear memory consolidation or dampened fear reaction during fear extinction. Sixty-six healthy participants were randomly assigned either to a group that received tDCS after fear acquisition (and before fear memory consolidation), to a group that received tDCS directly before fear extinction, or to a control group that never received active stimulation (sham). Differential skin conductance response (SCR) to CS+ vs. CS- was significantly decreased in both tDCS-groups compared to sham group. Our region of interest, the vmPFC, was stimulated best focally with a lateral anode position and a cathode on the contralateral side. But this comes along with a slightly lateral stimulation of vmPFC depending on whether anode is placed left or right. To avoid unintended effects of stimulated sides the two electrode montages (anode left or right) were mirror-inverted which led to differential effects in SCR and electrocortical (mainly late positive potential [LPP]) data in our exploratory analyses. Results indicated that tDCS-timing is relevant for fear reactions via disturbed fear memory consolidation as well as fear expression, and this depends on whether vmPFC is stimulated with either left- or right-sided anode electrode montage. Electrocortical data can shed more light on the underlying neural correlates and exaggerated LPP seems to be associated with disturbed fear memory consolidation and dampened SCR to CS+ vs. CS-, but solely in the right anode electrode montage. Further open questions addressing where and when to stimulate the prefrontal brain in the course of augmenting fear extinction are raised.

The effect of hair type and texture on electroencephalography and event-related potential data quality.

Research utilizing event-related potential (ERP) methods is generally biased with regard to sample representativeness. Among the myriad of factors that contribute to sample bias are researchers' assumptions about the extent to which racial differences in hair texture, volume, and style impact electrode placement, and subsequently, study eligibility. The current study examines these impacts using data collected from n = 213 individuals ages 17-19 years, and offers guidance on collection of ERP data across the full spectrum of hair types. Individual differences were quantified for hair texture using a visual scale, and for hair volume by measuring the amount of gel used in cap preparation. Electroencephalography data quality was assessed with multiple metrics at the preprocessing, post-processing, and variable generation stages. Results indicate that hair volume is associated with small, but systematic differences in signal quality and signal amplitude. Such differences are highly problematic as they could be misattributed to cognitive differences among groups. However, inclusion of gel volume as a covariate to account for individual differences in hair volume significantly reduced, and in most cases eliminated, group differences. We discuss strategies for overcoming real and perceived technical barriers for researchers seeking to achieve greater inclusivity and representativeness in ERP research.

Exploring Electrode Placements to Optimize the Identification and Measurement of Early Auditory Evoked Potentials.

Cochlear synaptic loss (termed cochlear synaptopathy) has been suggested to contribute to suprathreshold hearing difficulties. However, its existence and putative effects in humans remain inconclusive, largely due to the heterogeneous methods used across studies to indirectly evaluate the health of cochlear synapses. There is a need to standardize proxies of cochlear synaptopathy to appropriately compare and interpret findings across studies. Early auditory evoked potentials (AEPs), including the compound action potential (AP)/Wave I of the auditory brainstem response are a popular proxy, yet remain variable based on technical considerations. This study evaluated one such consideration-electrode array (i.e., montage)-to optimize the use of early AEP waveforms. In 35 young adults, electrocochleography (ECochG) responses were collected using vertical and horizontal montages. Standard ECochG measures and AP/Wave I and Wave II peak-to-trough amplitudes and latencies were compared between montages. Vertical montage recordings consistently produced significantly larger AP/Wave I peak-to-trough amplitudes compared to horizontal recordings. These findings support the use of a vertical electrode montage for optimal recordings of peripheral cochlear nerve activity. As cochlear synaptopathy continues to be explored in humans, the methods highlighted here should be considered in the development of a standardized assessment.

Association between pulse width and health-related quality of life after electroconvulsive therapy in patients with unipolar or bipolar depression: an observational register-based study

Aims To examine the association between pulse width and HRQoL measured within one week after electroconvulsive therapy (ECT) and at six-month follow-up in patients with unipolar or bipolar depression. Methods This was an observational register study using data from the Swedish National Quality Registry for ECT (2011–2019). Inclusion criteria were: age ≥18 years; index treatment for unipolar/bipolar depression; unilateral electrode placement; information on pulse width; EQ-5D measurements before and after ECT. Multiple linear regressions were performed to investigate the association between pulse width (<0.5 ms; 0.5 ms; >0.5 ms) and HRQoL (EQ-5D-3L index; EQ VAS) one week after ECT (primary outcome) and six months after ECT (secondary outcome). Results The sample included 5,046 patients with unipolar (82%) or bipolar (18%) depression. At first ECT session, 741 patients (14.7%) had pulse width <0.5 ms, 3,639 (72.1%) had 0.5 ms, and 666 (13.2%) had >0.5 ms. There were no statistically significant associations between pulse width and HRQoL one week after ECT. In the subsample of patients with an EQ-5D index recorded six months after ECT (n = 730), patients receiving 0.5 ms had significantly lower HRQoL (−0.089) compared to <0.5 ms, after adjusting for demographic and clinical characteristics (p = .011). The corresponding analysis for EQ VAS did not show any statistically significant associations. Conclusion No robust associations were observed between pulse width and HRQoL after ECT. On average, significant improvements in HRQoL were observed one week and six months after ECT for patients with unipolar or bipolar disease, independent of the pulse width received.

Electroconvulsive Therapy Across Nations: A 2022 Survey of Practice.

We aimed to characterize worldwide electroconvulsive therapy (ECT) practice and compare practice across nations and global regions. Our anonymous survey was open on SurveyMonkey.com from January to June 2022. We sent invitations to providers identified using a Medicare provider database, an advanced PubMed search function, and professional group listservs. Participants were instructed to submit one survey per ECT site. Response frequencies were pooled by global region and compared using nonparametric methods. Responses came from 126 sites, mostly in the United States (59%, n = 74), Europe (18%, n = 23), Canada (10%, n = 12), and South/East Asia (6%, n = 8). With some exceptions, sites were broadly consistent in practice as indicated by: a likely shift internationally from bitemporal to right unilateral electrode placement; predominant use of pulse widths <1 ms; preference for seizure threshold titration over age-based dosing methods; widespread availability of continuation/maintenance ECT (97%); and frequent use of quantitative outcome measures for depressive symptoms (88%) and cognitive adverse effects (80%). This is the first, published survey that aimed to characterize worldwide ECT practice. With some exceptions, responses suggest a concordance in practice. However, responses were primarily from the Global North. To obtain a truly worldwide characterization of practice, future surveys should include more responses from the Global South.

Robotic-Assisted Navigation for Stereotactic Neurosurgery: A Cadaveric Investigation of Accuracy, Time, and Radiation.

Despite frequent use, stereotactic head frames require manual coordinate calculations and manual frame settings that are associated with human error. This study examines freestanding robot-assisted navigation (RAN) as a means to reduce the drawbacks of traditional cranial stereotaxy and improve targeting accuracy. Seven cadaveric human torsos with heads were tested with 8 anatomic coordinates selected for lead placement mirrored in each hemisphere. Right and left hemispheres of the brain were randomly assigned to either the traditional stereotactic arc-based (ARC) group or the RAN group. Both target accuracy and trajectory accuracy were measured. Procedural time and the radiation required for registration were also measured. The accuracy of the RAN group was significantly greater than that of the ARC group in both target (1.2 ± 0.5 mm vs 1.7 ± 1.2 mm, P = .005) and trajectory (0.9 ± 0.6 mm vs 1.3 ± 0.9 mm, P = .004) measurements. Total procedural time was also significantly faster for the RAN group than for the ARC group (44.6 ± 7.7 minutes vs 86.0 ± 12.5 minutes, P < .001). The RAN group had significantly reduced time per electrode placement (2.9 ± 0.9 minutes vs 5.8 ± 2.0 minutes, P < .001) and significantly reduced radiation during registration (1.9 ± 1.1 mGy vs 76.2 ± 5.0 mGy, P < .001) compared with the ARC group. In this cadaveric study, cranial leads were placed faster and with greater accuracy using RAN than those placed with conventional stereotactic arc-based technique. RAN also required significantly less radiation to register the specimen's coordinate system to the planned trajectories. Clinical testing should be performed to further investigate RAN for stereotactic cranial surgery.

Effect of Return Electrode Placement at Apical Cochleostomy on Current Flow With a Cochlear Implant.

A method for stimulating the cochlear apex using perimodiolar electrode arrays is described. This method involves implanting an electrode (ECE1) into the helioctrema in addition to standard cochlear implant placement. One objective is to verify a suitable approach for implanting ECE1 in the helicotrema. Another is to determine how placement of ECE1 reshapes electric fields. Two cadaveric half-heads were implanted, and electric voltage tomography was measured with ECE1 placed in many positions. An approach for placing ECE1 was identified. Changes in electric fields were only observed when ECE1 was placed into the fluid in the helicotrema. When inside the helicotrema, electric voltage tomography modeling suggests an increased current flow toward the apex. Placement of ECE1 into the cochlear apex is clinically feasible and has the potential to reshape electric fields to stimulate regions of the cochlea more apical than those represented by the electrode array.

Improved Configurations for 3D Acoustoelectric Tomography With a Minimal Number of Electrodes.

Acoustoelectric tomography (AET) is a hybrid imaging technique combining ultrasound and electrical impedance tomography (EIT). It exploits the acoustoelectric effect (AAE): an US wave propagating through the medium induces a local change in conductivity, depending on the acoustoelectric properties of the medium. Typically, AET image reconstruction is limited to 2D and most cases employ a large number of surface electrodes. This article investigates the detectability of contrasts in AET. We characterize the AEE signal as a function of the medium conductivity and electrode placement, using a novel 3D analytical model of the AET forward problem. The proposed model is compared to a finite element method simulation. In a cylindrical geometry with an inclusion contrast of 5 times the background and two pairs of electrodes, the maximum, minimum, and mean suppression of the AEE signal are 68.5%, 3.12%, and 49.0%, respectively, over a random scan of electrode positions. The proposed model is compared to a finite element method simulation and the minimum mesh sizes required successfully model the signal is estimated. We show that the coupling of AAE and EIT leads to a suppressed signal and the magnitude of the reduction is a function of geometry of the medium, contrast and electrode locations. This model can aid in the reconstruction of AET images involving a minimum number of electrodes to determine the optimal electrode placement.

Virtual brain model‐guided optimization of transcranial direct current stimulation in Alzheimer’s disease

AbstractBackgroundNon‐invasive brain stimulation techniques such as transcranial direct current stimulation (tDCS) can potentially counteract disrupted local and distributed brain network activity in Alzheimer’s disease (AD) with a beneficial effect on cognition. However, results of tDCS studies in AD up till now are inconsistent, probably partly due to different methodological choices such as electrode placement. We therefore explored tDCS optimization using a virtual brain network model of AD. Our aim was to compare a large, representative set of virtual tDCS intervention setups, to identify and potentially explain the optimal theoretical tDCS electrode positions for reducing or restoring functional network disruption.MethodWe simulated 20 tDCS setups in a computational macroscopic dynamic network model of 78 neural masses, coupled according to human structural topology. AD network damage was simulated using an activity‐dependent degeneration algorithm, which produces typical gradual oscillatory slowing and loss of connectivity. Current flow modeling was used to estimate tDCS‐targeted cortical regions for different electrode positions, and excitability of the pyramidal neurons of the corresponding neural masses was modulated to simulate tDCS. Outcome measures were relative power spectral density in the lower (8‐10 Hz) and upper (8‐13 Hz) alpha bands, total spectral power, posterior alpha peak frequency, and connectivity measures phase lag index (PLI) and amplitude envelope correlation (AEC).ResultThe performance of different tDCS strategies varied considerably, with best setups temporarily improving all spectral and connectivity outcome measures, while other setups had little to no effect, or even caused network deterioration. The best performing setup involved right parietal anodal stimulation, with a contralateral supraorbital cathode. A clear correlation between the network role of a region (e.g. hub) and its involvement in successful tDCS was not observed.ConclusionModeling tDCS produces specific, falsifiable predictions on how to counter disrupted brain dynamics in AD. In follow‐up studies, our general predictions will be compared to those of personalized virtual models, and then validated with tDCS‐magnetoencephalography (MEG) in a clinical AD patient cohort. This modeling‐informed approach can guide and perhaps accelerate tDCS therapy development, as well as enhance our understanding of tDCS effects.

Distally-referred surface electrical nerve stimulation (DR-SENS) for haptic feedback

Objective. This study’s objective is to understand distally-referred surface electrical nerve stimulation (DR-SENS) and evaluates the effects of electrode placement, polarity, and stimulation intensity on the location of elicited sensations in non-disabled individuals. Approach. A two-phased human experiment was used to characterize DR-SENS. In Experiment One, we explored 182 electrode combinations to identify a subset of electrode position combinations that would be most likely to elicit distally-referred sensations isolated to the index finger without discomfort. In Experiment Two, we further examined this subset of electrode combinations to determine the effect of stimulation intensity and electrode position on perceived sensation location. Stimulation thresholds were evaluated using parameter estimation by sequential testing and sensation locations were characterized using psychometric intensity tests. Main Results. We found that electrode positions distal to the wrist can consistently evoke distally referred sensations with no significant polarity dependency. The finger-palm combination had the most occurrences of distal sensations, and the different variations of this combination did not have a significant effect on sensation location. Increasing stimulation intensity significantly expanded the area of the sensation, moved the most distal sensation distally, and moved the vertical centroid proximally. Also, a large anodic-leading electrode at the elbow mitigated all sensation at the anodic-leading electrode site while using symmetric stimulation waveforms. Furthermore, this study showed that the most intense sensation for a given percept can be distally referred. Lastly, for each participant, at least one of the finger-palm combinations evaluated in this study worked at both perception threshold and maximum comfortable stimulation intensities. Significance. These findings show that a non-invasive surface electrical stimulation charge modulated haptic interface can be used to elicit distally-referred sensations on non-disabled users. Furthermore, these results inform the design of novel haptic interfaces and other applications of surface electrical stimulation based haptic feedback on electrodes positioned distally from the wrist.