Electrode Location Research Articles

Emerging evidence on the effects of electrode arrangements and other parameters on the application of transcutaneous spinal direct current stimulation.

Transcutaneous spinal direct current stimulation (TSDCS) has the potential to modulate spinal circuits and induce functional changes in humans. Nevertheless, differences across studies on basic parameters used and obtained metrics represent a confounding factor. Computer simulations are instrumental in improving the application of the TSDCS technique. Their findings allow a better interpretation of the tissue conductivities heterogeneity. Emerging findings indicate the electric field is maximal in the segments located between the electrodes and that factors such as the depth of the targeted area, and location of the electrodes on low conductive points, such as the spinous processes, may impact the electric field generated in the spinal cord, with consequences for thoracic versus lumbar or cervical applications. Recently, growing attention has been directed toward the importance of the TSDCS reference electrode's position and its influence on the current field properties at the targeted site. This review highlights the influence of dosage, polarity, and electrode position on the variety of TSDCS results in healthy and some clinical populations. Based on the available evidence, we suggest that although the current dosage appears to have a negligible effect, the variety of electrode montages and configurations of TSDCS can significantly impact the electric field distributions and potentially explain the conflicting results of experimental studies. Future human trials should systematically and thoughtfully evaluate the location of TSDCS electrodes based on the targeted neural structures.

Does the audiogram shape influence the intracochlear recording of Electrocochleography during and after cochlear implantation?

During cochlear implant (CI) surgery, it is desirable to perform intraoperative measurements such as Electrocochleography (ECochG) to monitor the inner ear function and thereby to support the preservation of residual hearing. However, a significant challenge arises as the recording location of intracochlear ECochG via the CI electrode changes during electrode insertion. This study aimed to investigate the relationships between intracochlear ECochG recordings, the position of the recording contact within the cochlea relative to its anatomy, and the implications for frequency and residual hearing preservation. Intraoperative ECochG recordings were conducted using the CI electrode (MED-EL) during the insertion of hearing preservation electrodes and after the insertion process. Recordings were continuously conducted using the most apical electrode (contact 1) during insertion. After insertion, the recordings were performed on all different electrode contacts. The electrode location in the cochlea during insertion was estimated using mathematical models and preoperative clinical imaging, while the postoperative electrode position was determined using postoperative clinical imaging. The study involved 10 adult CI recipients. In those with good low-frequency hearing, an increase in signal amplitude was observed, with the highest amplitudes closest to the stimulation frequency generators, and no phase change was observed. Conversely, patients with flat hearing loss exhibited a second peak with an opposite phase in the medial area of the cochlea. This study is the first to suggest that the pattern of the preoperative audiogram may influence the ECochG outcomes measured intraoperatively. Specifically, the ECochG responses during insertion appeared to behave as expected with good low-frequency hearing, while with flat hearing loss there appear to be further effects. These findings indicate that this approach can provide valuable information for the interpretation of intracochlearly recorded ECochG signals.

Semantic Context Effects in Picture and Sound Naming: Evidence from Event-related Potentials and Pupillometric Data.

When a picture is repeatedly named in the context of semantically related pictures, (homogeneous context) responses are slower than when the picture is repeatedly named in the context of unrelated pictures (heterogeneous context). This semantic interference effect in blocked-cyclic naming plays an important role in devising theories of word production. Wöhner, Mädebach, and Jescheniak [2021; Wöhner, S., Mädebach, A., & Jescheniak, J. D. Naming pictures and sounds: Stimulus type affects semantic context effects. Journal of Experimental Psychology: Human Perception and Performance, 47, 716-730, 2021] have shown that the effect is substantially larger when participants name environmental sounds than when they name pictures. We investigated possible reasons for this difference, using EEG and pupillometry. The behavioral data replicated Wöhner and colleagues. ERPs were more positive in the homogeneous compared with the heterogeneous context over central electrode locations between 140-180 msec and 250-350 msec for picture naming and between 250 and 350 msec for sound naming, presumably reflecting semantic interference during semantic and lexical processing. The later component was of similar size for pictures and sounds. ERPs were more negative in the homogeneous compared with the heterogeneous context over frontal electrode locations between 400 and 600 msec only for sounds. The pupillometric data showed a stronger pupil dilation in the homogeneous compared with the heterogeneous context only for sounds. The amplitudes of the late ERP negativity and pupil dilation predicted naming latencies for sounds in the homogeneous context. The latency of the effects indicates that the difference in semantic interference between picture and sound naming arises at later, presumably postlexical processing stages closer to articulation. We suggest that the processing of the auditory stimuli interferes with phonological response preparation and self-monitoring, leading to enhanced semantic interference.

Boundary Complexity of (Sub-) Cortical Areas Predict Deep Brain Stimulation Outcomes in Parkinson's Disease.

While deep brain stimulation (DBS) remains an effective therapy for Parkinson's disease (PD), sources of variance in patient outcomes are still not fully understood, underscoring a need for better prognostic criteria. Here we leveraged routinely collected T1-weighted (T1-w) magnetic resonance imaging (MRI) data to derive patient-specific measures of brain structure and evaluate their usefulness in predicting changes in PD medications in response to DBS. Preoperative T1-w MRI data from 231 patients with PD were used to extract regional measures of fractal dimension (FD), sensitive to the structural complexities of cortical and subcortical areas. FD was validated as a biomarker of Parkinson's disease (PD) progression through comparison of patients with PD and healthy controls (HCs). This analysis revealed significant group differences in FD across nine brain regions which supports its utility as a marker of PD. We evaluated the impact of adding imaging features (FD) to a clinical model that included demographics and clinical parameters-age, sex, total number and location of DBS electrodes, and preoperative motor response to levodopa. This model aimed to explain variance and predict changes in medication following DBS. Regression analysis revealed that inclusion of the FD of distributed brain areas correlated with post-DBS reductions in medication burden, explaining an additional 13.6% of outcome variance (R 2 =0.388) compared to clinical features alone (R 2 =0.252). Hypergraph-based classification learning tasks achieved an area under the receiver operating characteristic curve of 0.64 when predicting with clinical features alone, versus 0.76 when combining clinical and imaging features. These findings demonstrate that PD effects on brain morphology linked to disease progression influence DBS outcomes. The work also highlights FD as a potentially useful imaging biomarker to enhance DBS candidate selection criteria for optimized treatment planning.

Evoking stable and precise tactile sensations via multi-electrode intracortical microstimulation of the somatosensory cortex.

Tactile feedback from brain-controlled bionic hands can be partially restored via intracortical microstimulation (ICMS) of the primary somatosensory cortex. In ICMS, the location of percepts depends on the electrode's location and the percept intensity depends on the stimulation frequency and amplitude. Sensors on a bionic hand can thus be linked to somatotopically appropriate electrodes, and the contact force of each sensor can be used to determine the amplitude of a stimulus. Here we report a systematic investigation of the localization and intensity of ICMS-evoked percepts in three participants with cervical spinal cord injury. A retrospective analysis of projected fields showed that they were typically composed of a focal hotspot with diffuse borders, arrayed somatotopically in keeping with their underlying receptive fields and stable throughout the duration of the study. When testing the participants' ability to rapidly localize a single ICMS presentation, individual electrodes typically evoked only weak sensations, making object localization and discrimination difficult. However, overlapping projected fields from multiple electrodes produced more localizable and intense sensations and allowed for a more precise use of a bionic hand.

Dynamics of magnetic cortico-cortical responses evoked by single-pulse electrical stimulation.

Intracranial single-pulse electrical stimulation (SPES) can elicit cortico-cortical evoked potentials. Their investigation with intracranial EEG is biased by the limited number and selected location of electrodes, which could be circumvented by simultaneous non-invasive whole-scalp recording. This study aimed at investigating the ability of magnetoencephalography (MEG) to characterize cortico-cortical evoked fields (CCEFs) and effective connectivity between the epileptogenic zone (EZ) and non-epileptogenic zone (i.e., non-involved [NIZ]). A total of 301 SPES trains (at 0.9 Hz during 120 s) were performed in 10 patients with refractory focal epilepsy. MEG signals were denoised, epoched, averaged, and decomposed using independent component analysis. Significant response deflections and significant source generators were detected. Peak latency/amplitude were compared between each different cortical/subcortical structure of the NIZ containing more than five SPES, and then between the EZ and corresponding brain structures in the NIZ. MEG detected and localized polymorphic/polyphasic CCEFs, including one to eight significant consecutive deflections. The latency and amplitude of CCEFs within the NIZ differed significantly depending on the stimulated brain structure. Compared with the corresponding NIZ, SPES within the extratemporal EZ demonstrated delayed CCEF latency, whereas SPES within the temporal EZ showed decreased CCEF amplitude. SPES within the EZ elicited a significantly higher rate of CCEFs within the stimulated lobe compared with those within the NIZ. This study reveals polymorphic CCEFs with complex spatiotemporal dynamics both within the NIZ and EZ. It highlights significant differences in effective connectivity of the epileptogenic network. These cortico-cortical evoked responses could thus contribute to increasing the yield of intracranial recordings.

ECG analysis of ventricular fibrillation dynamics reflects ischaemic progression subject to variability in patient anatomy and electrode location.

Ventricular fibrillation (VF) is the deadliest arrhythmia, often caused by myocardial ischaemia. VF patients require urgent intervention planned quickly and non-invasively. However, the accuracy with which electrocardiographic (ECG) markers reflect the underlying arrhythmic substrate is unknown. We analysed how ECG metrics reflect the fibrillatory dynamics of electrical excitation and ischaemic substrate. For this, we developed a human-based computational modelling and simulation framework for the quantification of ECG metrics, namely, frequency, slope, and amplitude spectrum area (AMSA) during VF in acute ischaemia for several electrode configurations. Simulations reproduced experimental and clinical findings in 21 scenarios presenting variability in the location and transmural extent of regional ischaemia, and severity of ischaemia in the remote myocardium secondary to VF. Regional acute myocardial ischaemia facilitated re-entries, potentially breaking up into VF. Ischaemia in the remote myocardium modulated fibrillation dynamics. Cases presenting a mildly ischaemic remote myocardium yielded sustained VF, enabled by the high proliferation of phase singularities (PS, 11-22) causing remarkably disorganised activation patterns. Conversely, global acute ischaemia induced stable rotors (3-12 PS). Changes in frequency and morphology of the ECG during VF reproduced clinical findings but did not show a direct correlation with the underlying wave dynamics. AMSA allowed the precise stratification of VF according to ischaemic severity in the remote myocardium (healthy: 23.62-24.45 mV Hz; mild ischaemia: 10.58-21.47 mV Hz; moderate ischaemia: 4.82-11.12 mV Hz). Within the context of clinical reference values, apex-anterior and apex-posterior electrode configurations were the most discriminatory in stratifying VF based on the underlying ischaemic substrate. This in silico study provides further insights into non-invasive patient-specific strategies for assessing acute ventricular arrhythmias. The use of reliable ECG markers to characterise VF is critical for developing tailored resuscitation strategies.

Individuals with psychosis receive less electric field strength during transcranial direct current stimulation compared to healthy controls

Recent research has examined the effectiveness of transcranial direct current stimulation (tDCS) as an adjunctive treatment for antipsychotics, finding mixed results on cognitive, positive, and negative symptoms. We tested if individuals with psychosis have reduced electric field strength compared to healthy controls and assessed the potential causal factors. We hypothesized that either cortical thinning due to the disorder or increased scalp thickness due to secondary effects of the disorder were causal factors. Using the Psychosis Human Connectome Project dataset, we simulated electric field models for 136 individuals with psychosis, 73 first-degree relatives, and 43 healthy controls. We compared group differences of electric field strength at bilateral dorsolateral prefrontal cortex (dlPFC), targeted with two montages (Fp1-Fp2 & F3-Fp2) commonly used to treat cognitive impairment. We additionally compared groups on scalp, skull, and cerebrospinal fluid thickness at bilateral dlPFC and the three electrode locations. Mediation analyses assessed if tissue thickness and BMI were causal factors for group differences while controlling for age and sex. Individuals with psychosis had lower electric field strength for bilateral dlPFC for both montages. Scalp thickness was also greater for individuals with psychosis, but cerebrospinal fluid thickness was not significantly different. BMI was a significant mediator for the group difference seen in both scalp thickness and electric field strength. Future treatment studies using tDCS in the psychosis population should include electric field modeling to assess its effectiveness given the increased risk of obesity. Individualized montages based on head models may also improve effectiveness.

The relationships between cochlear nerve health and AzBio sentence scores in quiet and noise in postlingually deafened adult cochlear implant users.

This study investigated the relationships between the cochlear nerve (CN) health and sentence-level speech perception outcomes measured in quiet and noise in postlingually deafened adult cochlear implant (CI) users. Study participants included 24 postlingually deafened adult CI users with a Cochlear® Nucleus™ device. For each participant, only one ear was tested. Neural health of the CN was assessed at three or four electrode locations across the electrode array using two parameters derived from results of the electrically evoked compound action potential (eCAP). One parameter was the phase locking value (PLV) which estimated neural synchrony in the CN. The other parameter was the sensitivity of the eCAP amplitude growth function (AGF) slope to changes in the interphase gap (IPG) of biphasic electrical pulses (i.e., the IPGEslope). Speech perception was tested using AzBio sentences in both quiet and a ten-talker babble background noise with +5 dB and +10 dB signal-to-noise ratios (SNR). IPGEslope and PLV values were averaged across electrodes for each subject, both with and without weighting by the frequency importance function (FIF) of the AzBio sentences. Pearson and Spearman correlations were used to assess the pairwise relationships between the IPGEslope, the PLV, and age. Multiple linear regression models with AzBio score as the outcome and the PLV and the IPGEslope as predictors were used to evaluate the associations between the three variables while controlling for age. The correlation between the IPGEslope and the PLV was negligible and not statistically significant. The PLV, but not the IPGEslope, differed significantly across electrodes, where the apical electrodes had larger PLVs (better neural synchrony) than the basal electrodes. The IPGEslope, but not the PLV, was significantly correlated with participant's age, where smaller IPGEslope values (poorer CN health) were associated with more advanced age. The PLV, but not the IPGEslope, was significantly associated with AzBio scores in noise, where larger PLVs predicted better speech perception in noise. Neither the PLV nor the IPGEslope was significantly associated with AzBio score in quiet. The result patterns remained the same regardless of whether the mean values of the IPGEslope and the PLV were weighted by the AzBio FIF. The IPGEslope and the PLV quantify different aspects of CN health. The positive association between the PLV and AzBio scores suggests that neural synchrony is important for speech perception in noise in adult CI users. The lack of association between age and the PLV indicates that reduced neural synchrony in the CN is unlikely the primary factor accounting for the greater deficits in understanding speech in noise observed in elderly, as compared to younger, CI users.

Electrode Location and Domain-Specific Cognitive Change Following Subthalamic Nucleus Deep Brain Stimulation for Parkinson's Disease.

Deep brain stimulation (DBS) is an effective treatment for Parkinson's disease (PD) motor symptoms. DBS is also associated with postoperative cognitive change in some patients. Previous studies found associations between medial active electrode contacts and overall cognitive decline. Our current aim is to determine the relationship between active electrode contact location and domain-specific cognitive changes. A single-institution retrospective cohort study was conducted in patients with PD who underwent subthalamic nucleus (STN) DBS from August 05, 2010, to February 22, 2021, and received preoperative and postoperative neuropsychological testing. Standardized norm-referenced test z-scores were categorized into attention, executive function, language, verbal memory, and visuospatial domains. SD change scores were averaged to create domain-specific change scores. We identified anterior commissure/posterior commissure coordinates of active electrode contacts in atlas space. We evaluated differences in active electrode contact location between patients with a domain score decrease of at least 1 SD and less than 1 SD. We performed multiple variable linear regression controlling for age, sex, education, time from surgery to postoperative neuropsychological testing (follow-up duration), disease duration, preoperative unified Parkinson's disease rating scale off medication scores, and preoperative memory scores to determine the relationship between active electrode contact location and domain change. A total of 83 patients (male: n = 60, 72.3%) were included with a mean age of 63.6 ± 8.3 years, median disease duration of 9.0 [6.0, 11.5] years, and median follow-up duration of 8.0 [7.0, 11.0] months. More superior active electrode contact location in the left STN (P = .002) and higher preoperative memory scores (P < .0001) were associated with worsening memory. Active electrode contact location was not associated with change in other domains. In patients with PD who underwent STN DBS, we found an association between superior active electrode contacts in the left STN and verbal memory decline. Our study increases understanding of factors associated with cognitive change after DBS and may help inform postoperative programming.

Mark3D - A semi-automated open-source toolbox for 3D head- surface reconstruction and electrode position registration using a smartphone camera video.

Source localization in EEG necessitates co-registering the EEG sensor locations with the subject's MRI, where EEG sensor locations are typically captured using electromagnetic tracking or 3D scanning of the subject's head with EEG cap, using commercially available 3D scanners. Both methods have drawbacks, where, electromagnetic tracking is slow and immobile, while 3D scanners are expensive. Photogrammetry offers a cost-effective alternative but requires multiple photos to sample the head, with good spatial sampling to adequately reconstruct the head surface. Post-reconstruction, the existing tools for electrode position labelling on the 3D head-surface have limited visual feedback and do not easily accommodate customized montages, which are typical in multi-modal measurements. We introduce Mark3D, an open-source, integrated tool for 3D head-surface reconstruction from phone camera video. It eliminates the need for keeping track of spatial sampling during image capture for video-based photogrammetry reconstruction. It also includes blur detection algorithms, a user-friendly interface for electrode and tracking, and integrates with popular toolboxes such as FieldTrip and MNE Python. The accuracy of the proposed method was benchmarked with the head-surface derived from a commercially available handheld 3D scanner Einscan-Pro + (Shining 3D Inc.,) which we treat as the "ground truth". We used reconstructed head-surfaces of ground truth (G1) and phone camera video (M1080) to mark the EEG electrode locations in 3D space using a dedicated UI provided in the tool. The electrode locations were then used to form pseudo-specific MRI templates for individual subjects to reconstruct source information. Somatosensory source activations in response to vibrotactile stimuli were estimated and compared between G1 and M1080. The mean positional errors of the EEG electrodes between G1 and M1080 in 3D space were found to be 0.09 ± 0.01mm across different cortical areas, with temporal and occipital areas registering a relatively higher error than other regions such as frontal, central or parietal areas. The error in source reconstruction was found to be 0.033 ± 0.016mm and 0.037 ± 0.017mm in the left and right cortical hemispheres respectively.

Neurophysiological Correlates of Expert Knowledge: An Event-Related Potential (ERP) Study about Law-Relevant Versus Law-Irrelevant Terms.

The evaluation of evidence, which frequently takes the form of scientific evidence, necessitates the input of experts in relevant fields. The results are presented as expert opinions or expert evaluations, which are generally accepted as a reliable representation of the facts. A further issue that remains unresolved though is the process of evaluating the expertise and knowledge of an expert in the first instance. In general, earned certificates, grades and other objective criteria are typically regarded as representative documentation to substantiate an expert status. However, there is a possibility that these may not always be sufficiently representative. The goal of the present study was to provide evidence that the neural processing of law-relevant and law-irrelevant terms varies significantly between participants who have received training in the field of law (experts) and those who have not (novices). To this end, changes in brain activity were recorded via electroencephalography (EEG) during visual presentations of terms belonging to five different categories (fake right, democracy, filler word, basic right and rule of law). Event-related potentials (ERPs) were subsequently averaged for each category and subjected to statistical analysis. The results clearly demonstrate that participants trained in law processed fake rights and filler words in a similar manner. Furthermore, both of these conditions elicited different levels of brain activity compared to all law-relevant terms. This was not the case in participants who had not received legal training. The brains of untrained participants processed all five term categories in a strikingly similar manner. In light of prior knowledge regarding language processing, the primary focus was on two distinct electrode locations: one in the left posterior region, and the other in the left frontal region. In both locations, the most prominent differences in brain activity elicited by the aforementioned term categories in law-trained participants occurred approximately 450 milliseconds after stimulus onset. The results were further corroborated by a repeated-measures ANOVA and subsequent t-tests, which also demonstrated the absence of this effect in law-untrained participants. The findings of this study provide empirical evidence that brain activity measurements, in particular ERPs, can be used to distinguish between experts trained in a specific field of expertise and novices in that field. Such findings have the potential to facilitate objective assessments of expertise, enabling comparisons between experts and novices that extend beyond traditional criteria such as qualifications and experience. Instead, individuals can be evaluated based on their cognitive processes, as observed through brain activity.

Development of three-dimensional forward modeling method for the magnetometric resistivity (MMR) method

We have developed a 3-D forward modeling method for the magnetometric resistivity (MMR) technique, specially focusing on the marine MMR method, which utilizes a vertical bipole source and seafloor receivers to measure magnetic field variations. The bipole source generates an artificial electric current between two electrodes: one on the sea surface and another on the seafloor. When computing the electric potential using the relaxation method, while conserving electric current, singularities arise at the electrode locations. To address this issue, we introduce two electrical resistivity structures to mitigate the effects of these singularities and to obtain magnetic field anomalies caused by arbitrary 3-D electrical resistivity anomalies beneath the seafloor. By determining the sign of the magnetic field anomaly, we can infer whether the electrical resistivity of the anomalous body is more conductive or more resistive compared to the surrounding oceanic crust. Furthermore, we demonstrate that increasing the number of bipole sources is more effective in exploring anomalous bodies than increasing the number of receivers.Graphical abstract

Analysis of projection welding in relation to the non-parallelism of electrodes

The article contains the analysis of projection welding in relation to the non-parallel location (non-parallelism) of electrodes. For a thin-walled flat element, e.g., sheet metal with two embossed projections, calculations were conducted for different angles between the upper electrode and the lower electrode. The calculation involved the use of the SORPAS 3D software. The analysis included the distribution of temperature, power density, electrode displacement, the volume of molten metal in the weld nugget, nugget diameters, and energy supplied to the weld. The article presents the comparison of results obtained for various angles between the electrodes of the welding machine. The results of numerical calculations were verified experimentally through technological welding tests and destructive tests (peeling/metallographic). The convergence of the experimental and numerical results was satisfactory. The tests involved a typical element used in the automotive industry, i.e., a nut with two embossed projections in the flat part. The article represents quite an innovative new approach to multiple-projection welding from a numerical calculation point of view. Such an approach allows the researcher to identify the phenomena taking place in the process. The article also presents a new approach to the analysis of multi-projection welding as regards the non-parallelism of electrodes. The results enabled the determination of phenomena taking place in the multi-projection welding process as well as the boundary conditions in relation to which the process became improper (unstable).

Investigating the Feasibility of Gap Prepulse Inhibition by Auditory Middle Latency Responses in Healthy Subjects

Background and Aim: Gap Prepulse Inhibition (GPI) is a type of Prepulse Inhibition (PPI) in which a gap is used as a prepulse. This study was conducted to investigate the silence gap effect on Auditory Middle Latency Response (AMLR) inhibition in normal subjects. Methods: In this study, 25 participants with normal hearing and no history of tinnitus were included. AMLR was recorded in response to stimuli with gap and without gap in two background noises of 2 and 8 kHz at two electrode locations Fz and Cz and then, gap prepulse inhibition for Na-Pa, Pa-Nb, Nb-Pb and Pb-Nc amplitude with Use of responses to stimuli with and without gap was calculated. Results: The results showed that the mean amplitudes of all four AMLR indices decreased in response to the stimuli with gap and this decrease was more and statistically significant in 8 kHz background noise (p≤0.001). Conclusion: According to the results of this study, it seems that in future studies, PPI of Na-Pa and Pb-Nc amplitudes can be used as main indicators and PPI of Pa-Nb and Nb-Pb amplitudes as alternative indicators in the PPI paradigm in tinnitus diagnosis. Keywords: Prepulse inhibition; tinnitus; auditory middle latency responses

Analysis of electrode locations on limb condition effect for myoelectric pattern recognition

BackgroundGesture recognition using surface electromyography (sEMG) has garnered significant attention due to its potential for intuitive and natural control in wearable human–machine interfaces. However, ensuring robustness remains essential and is currently the primary challenge for practical applications.MethodsThis study investigates the impact of limb conditions and analyzes the influence of electrode placement. Both static and dynamic limb conditions were examined using electrodes positioned on the wrist, elbow, and the midpoint between them. Initially, we compared classification performance across various training conditions at these three electrode locations. Subsequently, a feature space analysis was conducted to quantify the effects of limb conditions. Finally, strategies for group training and feature selection were explored to mitigate these effects.ResultsThe results indicate that with the state-of-the-art method, classification performance at the wrist was comparable to that at the middle position, both of which outperformed the elbow, consistent with the findings from the feature space analysis. In inter-condition classification, training under dynamic limb conditions yielded better results than training under static conditions, especially at the positions covered by dynamic training. Additionally, fast and slow movement speeds produced similar performance outcomes. To mitigate the effects of limb conditions, adding more training conditions reduced classification errors; however, this reduction plateaued after four conditions, resulting in classification errors of 22.72%, 22.65%, and 26.58% for the wrist, middle, and elbow, respectively. Feature selection further improved classification performance, reducing errors to 19.98%, 19.75%, and 27.14% at the respective electrode locations, using three optimal features derived from single-condition training.ConclusionsThe study demonstrated that the impact of limb conditions was mitigated when electrodes were placed near the wrist. Dynamic limb condition training, combined with feature optimization, proved to be an effective strategy for reducing this effect. This work contributes to enhancing the robustness of myoelectric-controlled interfaces, thereby advancing the development of wearable intelligent devices.

Global motor dynamics - Invariant neural representations of motor behavior in distributed brain-wide recordings

Objective.Motor-related neural activity is more widespread than previously thought, as pervasive brain-wide neural correlates of motor behavior have been reported in various animal species. Brain-wide movement-related neural activity have been observed in individual brain areas in humans as well, but it is unknown to what extent global patterns exist.Approach.Here, we use a decoding approach to capture and characterize brain-wide neural correlates of movement. We recorded invasive electrophysiological data from stereotactic electroencephalographic electrodes implanted in eight epilepsy patients who performed both an executed and imagined grasping task. Combined, these electrodes cover the whole brain, including deeper structures such as the hippocampus, insula and basal ganglia. We extract a low-dimensional representation and classify movement from rest trials using a Riemannian decoder.Main results.We reveal global neural dynamics that are predictive across tasks and participants. Using an ablation analysis, we demonstrate that these dynamics remain remarkably stable under loss of information. Similarly, the dynamics remain stable across participants, as we were able to predict movement across participants using transfer learning.Significance.Our results show that decodable global motor-related neural dynamics exist within a low-dimensional space. The dynamics are predictive of movement, nearly brain-wide and present in all our participants. The results broaden the scope to brain-wide investigations, and may allow combining datasets of multiple participants with varying electrode locations or calibrationless neural decoder.

Spatially Selective Retinal Ganglion Cell Activation Using Low Invasive Extraocular Temporal Interference Stimulation.

Conventional retinal implants involve complex surgical procedures and require invasive implantation. Temporal Interference Stimulation (TIS) has achieved noninvasive and focused stimulation of deep brain regions by delivering high-frequency currents with small frequency differences on multiple electrodes. In this study, we conducted in silico investigations to evaluate extraocular TIS's potential as a novel visual restoration approach. Different from the previously published retinal TIS model, the new model of extraocular TIS incorporated a biophysically detailed retinal ganglion cell (RGC) population, enabling a more accurate simulation of retinal outputs under electrical stimulation. Using this improved model, we made the following major discoveries: (1) the maximum value of TIS envelope electric potential ([Formula: see text] showed a strong correlation with TIS-induced RGC activation; (2) the preferred stimulating/return electrode (SE/RE) locations to achieve focalized TIS were predicted; (3) the performance of extraocular TIS was better than same-frequency sinusoidal stimulation (SSS) in terms of lower RGC threshold and more focused RGC activation; (4) the optimal stimulation parameters to achieve lower threshold and focused activation were identified; and (5) spatial selectivity of TIS could be improved by integrating current steering strategy and reducing electrode size. This study provides insights into the feasibility and effectiveness of a low-invasive stimulation approach in enhancing vision restoration.

Predictive Modeling of Sleep Slow Oscillation Emergence on the electrode manifold: Toward Personalized Closed-Loop Brain Stimulation.

Sleep slow oscillations (SOs), characteristic of NREM sleep, are causally tied to cognitive outcomes and the health-promoting homeostatic functions of sleep. Due to these known benefits, brain stimulation techniques aiming to enhance SOs are being developed, with great potential to contribute to clinical interventions, as they hold promise for improving sleep functions in populations with identified SO deficits (e.g., mild cognitive impairment). SO-targeting closed-loop stimulation protocols currently strive to identify SO occurrences in real time, a computationally intensive step that can lead to reduced precision (compared to post-hoc detection). These approaches are also often limited to focusing on only one electrode location, thus inherently precluding targeting of SOs that is informed by the overall organization of SOs in space-time. Prediction of SO emergence across the electrode manifold would establish an alternative to online detection, thus greatly advancing the development of personalized and flexible brain stimulation paradigms. This study presents a computational model that predicts SO occurrences at multiple locations across a night of sleep. In combination with our previous study on optimizing brain stimulation protocols using the spatiotemporal properties of SOs, this model contributes to increasing the accuracy of SO targeting in brain stimulation applications. SOs were detected in a dataset of nighttime sleep of 22 subjects (9 females), acquired with polysomnography including 64 EEG channels. Modeling of SO occurrence was achieved for SOs in stage N3, or in a combination of stages N2 and N3 (N2&N3). We study SO emergence at progressively more refined time scales. First, the cumulative SO occurrences in successive sleep cycles were successfully fit with exponentials. Secondly, the SO timing in each individual was modeled with a renewal point process. Using an inverse Gaussian model, we estimated the probability density function of SO timing and its parameters μ (mean) and λ (shape, representing skewness) in successive cycles. We observed a declining trend in the SO count across sleep cycles, which we modeled using a power law relationship. The decay rate per cycle was 1.473 for N3 and 1.139 for N2&N3, with variances of the decay rates across participants being 1 and 0.53, respectively. This pattern mirrors the declining trend of slow wave activity (SWA) across sleep cycles, likely due to the inherent relationship between SWA and SO. Additionally, the SO timing model for N3 showed an increasing trend in the model parameters (μ, λ) across cycles. The increase rate per cycle followed a power law relationship with a rate of 0.83 and an exponential relationship with a rate of 4.59, respectively. The variances of the increase rates were 0.02 for μ and 0.44 for λ across participants. This study establishes a predictive model for SO occurrence during NREM sleep, providing insights into its organization in successive cycles and at different EEG channels, which is relevant to development of personalized stimulation paradigms. These findings imply that personalized model parameters can be estimated by incorporating SO information in the first sleep cycle, and hence SO timing can be predicted before its occurrence with a probability distribution, enabling more precise targeting of SOs.

Landmark registration in CT for lung model approximation in EIT

Abstract For the visualization of pulmonary ventilation with Electrical Impedance Tomography (EIT), most devices rely on generalized reconstruction models. Yet, fixed thorax dimensions, predetermined electrode locations, and standard lung shapes lead to multiple sources of EIT imaging distortion. The following work compares reconstructions of a library model, a practical model based on landmark fitting, and a detailed model based on manual segmentation. CT images of five pigs were segmented into torso surface, electrode positions, and lung borders. Practical models were created with reduced data, registration, and fitting. Detailed models were created by using the complete segmentation data. After EIT reconstruction and tidal image calculation, the overlap of CT lung segmentation and ventilated voxel was calculated. Compared with the results of a standardized model, the practical model reached an average ventilation/segmentation-overlap difference of an additional 12 %, and the detailed model achieved an average difference of 10 %. In conclusion, the shift of reconstructed impedance towards the segmented lung region is similar in both models when compared to the standard model, while the practical model requires a considerably less amount of information.