EEG/ECoG/EMG publications

The hypothalamus is critical for regulating behaviors essential for survival and locomotion, but how it integrates internal needs and transmits locomotion commands to the spinal cord (SC) remains unclear. We found that glutamatergic neurons in lateral hypothalamic area (LHA) are essential for regulating motivated locomotor activity. Using single-neuron projectome analysis, trans-synaptic tracing, and optogenetic manipulation, we showed that LHA facilitates motivated locomotion during food seeking via pontine reticular nucleus, oral part (PnO) projection neurons, rather than direct SC projections or indirect stress signaling via medial septum and diagonal band. Activating PnO-SC projection neurons also initiated locomotion. Importantly, LHA-PnO projection neurons were crucial for regulating locomotor recovery following mouse spinal cord injury (SCI). Motor cortex signals gated LHA deep brain stimulation treatment markedly promoted long-term restoration of hindlimb motor functions after severe SCI. Thus, we have identified a hypothalamic-pontine-spinal pathway and the stimulation paradigm for potential therapeutic intervention after SCI.

Memory consolidation enables animals to draw on past experiences to guide future behavior. This process involves system- and synaptic-level changes and predominantly occurs during sleep. While hippocampal-cortical circuits are well studied in this context, the contributions of other systems, including dopaminergic circuits—key players in learning-related processes—remain poorly understood. Ventral tegmental area dopaminergic (VTA DA ) neurons are active during sleep and suggested to participate in memory consolidation processes; however, causal evidence for this is lacking. Using calcium-dependent fiber photometry, electrophysiology, and chemogenetic and optogenetic manipulations across learning paradigms, we explore the functions of VTA DA neuronal activity during sleep. We show that VTA DA activity during nonrapid eye movement sleep is experience dependent, is enhanced by motor skill and associative learning, facilitates motor skill memory consolidation, and exhibits a motor learning–dependent increase in temporal coordination with cortical spindle oscillations. Our findings uncover a previously unidentified function for VTA DA neurons in consolidating memories during sleep, advancing understanding of this central neuromodulator’s functions in regulating fundamental biological processes.

Obective. Bipolar re-referencing (BPRR), in which one electrode’s signal is subtracted from a neighboring electrode to produce a differential signal, can improve signal readability and refine localization for intracranial electroencephalography. There is wide variation in manufactured electrode array spacing, yet how BPRR affects specific frequencies at precise inter-electrode distances has not been systematically evaluated. Approach. Intracranial recordings with uniquely large numbers of electrodes were obtained for sixteen patients with drug-resistant epilepsy. We evaluated combinations of high-density subdural grid, depth, and strip electrodes ( n = 3,664, 742, and 336) with manufactured linear inter-electrode distances of 4, 5, and 10 mm, respectively. BPRR was performed using all possible electrode pairs ( n = 445 305 grid, 16 004 depth, 3278 strip) spanning distances from 2–60 mm. Multi-taper power spectra were generated separately for grid, depth, and strip contacts. Distances were consolidated across patients and anatomical areas for generalizability, and distance-related influences on task-related brain activity and quantitative interictal epileptiform discharge localization were evaluated. Main results. We identified 8 mm as a consistent reversal point for BPRR, below which low-frequency signals (<30 Hz) had consistently decreased power, and higher frequencies had increased power. Larger distances increased all broadband (2–200 Hz) signals. Task-related increases in superior temporal gyrus 50–200 Hz activity were consistently enhanced across 4–40 mm bipolar distances. There were non-significant difference trends between 4 and 8 mm re-referencing on epileptiform discharge detection. Significance. BPRR distance imposed specific transition points for distance and frequency (roughly 8 mm and ∼30 Hz, respectively) that produced differential effects on measurements of signal power. The consistency across brain regions and electrode types (depth, subdural) suggests these influences are physical brain bio-signal properties, potentially related to spatial wavelength of periodic oscillations in lower frequencies in contrast to more aperiodic activity in higher frequencies. A distance-frequency relation map is provided to help optimize neural signal biomarker quality for intracranial applications by guiding strategic re-referencing distance selection.

Context‐dependent sensory processing within the predictive coding framework relies on detecting mismatches between incoming stimuli and internal predictive models. Sensory deviants elicit prediction errors, seen as enhanced neural responses, that update these models and influence attention and behaviour. Although prediction errors have been widely observed across brain regions, the downstream processes remain poorly understood. In this study, we recorded electrocorticography in five urethane‐anaesthetised rats and identified cortical slow oscillations, characterised by spontaneous transitions between ‘Up’ and ‘Down’ states. Deviant stimuli in an auditory oddball paradigm evoked an initial positive prediction error, followed by a prolonged, all‐or‐nothing response which spread in a travelling wave across the cortex. Identified as putative evoked cortical Up states, these responses were not evoked by standards, omissions or a many‐standards control. Up states following deviants occurred more recently after a previous Up state when compared to spontaneous Up states. In preliminary data from an awake rat, long‐latency Up states were not present spontaneously or evoked. In a different rat, anaesthetic depth was key to spontaneous and evoked Up states, with more robust Up/Down states and more reliable triggering of Up states under deeper anaesthesia. These results suggest that sensory deviants may cause shifts in cortical state under anaesthesia, explaining the long‐latency mismatch response under anaesthesia and sleep.

Ionogels are promising for soft robotics, energy systems, and bioelectronic interfaces due to their high ionic conductivity and environmental stability. However, combining high strength and fracture resistance remains challenging. Here, we report composite ionogels with outstanding mechanical strength (~65.4 megapascal) and fracture energy (~607 kilojoules per square meter), capable of bearing more than 5000 times their own weight. These ionogels are developed by tailoring solvent-solute interactions to create a dense, hyperconnected nanofibrous polymer network. Solvent engineering regulates hydrogen bonding competition, facilitating the formation of robust interphase hydrogen bonds and a soft-hard biomimetic interface. Moreover, their antidrying, breathable nature enables multifunctional electrophysiological monitoring, making them ideal for wearable bioelectronics. Their ionic conductivity, drug-loading capacity, and antibacterial properties allow their use in advanced e-bandages for chronic wound healing. This generalizable strategy for ionogel design opens pathways toward strong, versatile, and biocompatible materials, particularly valuable for next-generation soft materials, wearable electronics, and tissue engineering.

During wake, sound‐evoked and spontaneous neural activity of the auditory cortex evolves in distinct subspaces, whereas anesthesia disrupts sound responses and merges these spaces. To evaluate if similar modifications of sound representation geometry explain sensory disconnection during sleep, large neural populations of the mouse auditory cortex are followed across slow‐wave sleep and wakefulness. It is observed that sleep dampens sound responses but preserves the geometry of sound representations such that they remain separate from spontaneous activity. Moreover, response dampening is strongly coordinated across neurons and varied throughout sleep, spanning from fully preserved response patterns to population response failures on a fraction of sound presentations. These failures rarely occurred in wakefulness and are more common during high spindle‐band activity. Therefore, in sleep, the auditory system preserves sound feature selectivity up to the cortex for detailed acoustic surveillance but concurrently implements an intermittent gating mechanism leading to local sensory disconnections.

As part of a deep brain stimulation (DBS) procedure, direct electrophysiological recordings from thalamic and basal ganglia circuits were obtained from a pediatric participant with secondary dystonia to examine the neural mechanisms of motor timing. The participant performed a two-phase repetitive timing task that began with synchronization to a series of externally presented auditory cues, followed by a continuation phase in which the participant maintained the movement rhythm without external guidance. Simultaneous recordings from stereoelectroencephalography (sEEG) leads implanted in the globus pallidus internus (GPi), subthalamic nucleus (STN), ventral oralis (Vo), centromedian nucleus (CM), and thalamic nuclei receiving projections from the cerebellum (ventral intermediate nucleus (VIM) and centrolateral nucleus (CL)) revealed behaviorally relevant neural dynamics. Local field potentials (LFPs) from recorded nuclei exhibited strong, time-locked responses during the synchronization phase, with reduced amplitudes during the continuation phase. Time-frequency analysis showed consistent power increases around the corresponding mean of the inter-response intervals (IRIs) in both behavioral output and neural signals, suggesting frequency-specific entrainment across circuits. These findings suggest of cerebellar-thalamic and basal ganglia contributions to temporal coordination.

Background CLN3 disease, also known as juvenile Batten disease, is a recessively inherited neurodevelopmental disorder caused by mutations in the CLN3 gene. It represents the most common form of Neuronal Ceroid Lipofuscinoses (NCLs), a group of lysosomal storage disorders that impair brain function. Clinical features include progressive vision loss, language impairment, and cognitive decline. The early onset of visual deficits complicates the neurological assessment of cognitive dysfunction, while the rarity of CLN3 cases limits the study of sex-specific disease trajectories in humans. Therefore, there is a critical need for objective, translational biomarkers to monitor disease progression and support therapeutic development in preclinical animal models. Methods Building on our recent studies in individuals with CLN3 disease, we developed a parallel experimental paradigm using high-density electroencephalography (EEG) in Cln3 knockout ( Cln3-/-) mice to longitudinally assess auditory neurophysiological changes. We applied a duration-based mismatch negativity (MMN) paradigm, similar to that used in our human studies, to evaluate automatic detection of auditory pattern changes in male and female mice between 3 and 9 months of age. Results Wild-type (WT) mice of both sexes showed robust and stable duration MMN responses across this age range. In contrast, Cln3-/- mice showed marked sex- and age-dependent deficits: female mutants displayed persistent MMN deficits, whereas male mutants exhibited early MMN abnormalities that unexpectedly improved with age. Auditory brainstem responses confirmed intact peripheral hearing in Cln3-/- mice, indicating a central origin for the observed abnormalities. Further analyses revealed that MMN impairments were driven by age- and sex-specific alterations in auditory evoked potentials to both standard and deviant stimuli. Conclusions These findings demonstrate sex- and age-dependent disruptions in central auditory processing in Cln3-/- mice and support auditory duration MMN as a sensitive, translational biomarker of brain dysfunction in CLN3 disease. This approach offers a functional, cross-species measure for tracking disease progression and evaluating therapeutic interventions in Batten disease.

Sensory issues are common in autism spectrum disorders (ASD) and can significantly affect daily living. The phenomena of gating and habituation of event-related potentials (ERPs) to repetitive stimuli have been suggested as potential biomarkers reflecting atypical sensory processing in ASD. Sensory hypersensitivity and anxiety are closely related in ASD, and habituation to emotionally evocative stimuli may serve as a more sensitive biomarker for sensory hypersensitivity symptoms. However, previous studies have primarily used tonal stimuli, and there has been little investigation into whether habituation to emotionally evocative sounds is impaired in ASD patients. In this study, we compared the degree of habituation of the P1-N1 peak-to-peak amplitude in response to repeated tones and fearful vocalizations between control and ASD groups. Contrary to expectations, no significant difference was observed for fearful vocalizations between the groups, while ASD patients showed significantly reduced habituation to tonal sounds in the left parieto-occipital region. Furthermore, we found a significant correlation between the degree of habituation to tonal sounds in the left parieto-occipital region and sensory hypersensitivity symptoms in ASD patients, and similar abnormalities in BTBR mice, an animal model of ASD. These results suggest that habituation to tonal sounds, rather than emotionally evocative stimuli, may serve as a translational biomarker reflecting sensory hypersensitivity symptoms.

Objective Transcranial current stimulation (tCS) is a promising technique to non-invasively modulate human brain activity. However, stimulation artifacts in EEG and MEG recordings severely hinder the study of its online effects. Approach Here, we introduce a new approach to account for these artifacts. The approach rests on two key ideas. First, we focus on interactions of tCS with intrinsic brain activity, which are absent for tCS artifacts. Second, rather than removing artifacts, we compare composite signals that share similar artifacts but potentially differ in the interaction of tCS with intrinsic brain activity. We follow a simple logic: if tCS does not interact with intrinsic brain activity, then neural activity during simultaneous sensory stimulation and tCS should equal the linear superposition of the neural effects of each applied alone. Any deviation from this prediction provides evidence for a neural interaction. Main results We tested this approach in a proof-of-principle MEG study, applying 10 Hz transcranial alternating current stimulation (tACS) during rest and during a 10 Hz visual flicker. We compared neural activity during simultaneous stimulation with that predicted by the linear superposition of flicker and tACS alone and found a phase-dependent interaction between tACS and flicker-evoked brain activity. Significance Our work establishes a novel approach to investigate online effects of tCS and suggests a state-dependent interaction of tACS with human brain activity.

Background: Optimizing deep brain stimulation (DBS) parameter settings requires postoperative adjustments through a time-consuming trial-and-error process. As such, researchers have been developing computational models to guide DBS programming. Despite growing interest in image-guided DBS technology, and recent adoption into clinical practice, the direct validation of the prediction accuracy remains limited. Objective: The objective of this study was to establish a comparative framework for validating the accuracy of various DBS computational modeling methodologies in predicting the activation of clinically relevant pathways using in vivo measurements from PD patients undergoing subthalamic (STN) DBS surgery. Methods: In this study, we compared the accuracy of six computational modeling variations for predicting the activation of the corticospinal/bulbar tract (CSBT) and cortico-subthalamic hyperdirect pathway (HDP) using very short- (<2 ms) and short-latency (2-4 ms) cortical evoked potentials (cEPs). We constructed the variations using three key factors: modeling method (Driving Force [DF] vs. Volume of Tissue Activated [VTA]), imaging space (native vs. normative), and anatomical representation (pathway vs. structure). The model performances were quantified using the coefficient of determination (R2) between the cEP amplitudes and percent pathway or structure activation. Results: We compared model accuracy for 11 PD patients. The DF-Native-Pathway model was the most accurate method for quantitatively predicting experimental subcortical pathway activations. Additionally, our analysis showed that using normative brain space significantly diminished the accuracy of model predictions. Conclusion: The choice of methodology should depend on the specific application and the required level of precision for the intended analysis. However, model parameters should be optimized to accurately predict known experimental activation measures.

Purpose: We aim to develop a robust method to improve the estimation accuracy of motor-evoked potential (MEP) recruitment curves (RCs), including motor threshold, in small-sample settings which typically involve fewer than 40 stimuli. Methods: We present a hierarchical Bayesian (HB) method to model MEP size as a rectified-logistic function of stimulation intensity. This method is designed to account for small samples, handle outliers without discarding data, quantify estimation uncertainty, and simulate synthetic data that closely matches real observations, useful for optimizing experimental design. We validate its performance on transcranial magnetic stimulation (TMS), epidural spinal cord stimulation (SCS), and synthetic TMS datasets, and provide an open-source library for Python, called hbMEP, for diverse applications. Results: The rectified-logistic outperformed sigmoidal functions in predictive accuracy on TMS and SCS datasets, as demonstrated through cross-validation. A mixture extension of the HB model improved robustness to outliers by further increasing its predictive accuracy. The HB model reduced threshold estimation error by up to 70% on sparse synthetic TMS data compared to non-hierarchical models. Bayesian estimation with the HB model reduced the required number of participants by at least 23% to detect a shift in threshold with 80% power, compared to frequentist testing. Empirical results on human SCS data further validated its applicability to real data. Conclusion: By improving accuracy on sparse data, our method minimizes the number of stimuli needed to probe each individual's neuromuscular parameters across multiple muscles simultaneously, thereby reducing session duration and the risk of inadvertent neuromodulation. Our approach provides a more statistically powerful and conclusive framework for inferring changes in threshold, and therefore corticospinal excitability. The hbMEP library streamlines and unifies the analysis of RCs across stimulation modalities and experimental paradigms.

Fragile X Syndrome (FXS) is a leading genetic cause of intellectual disability and autism-like behaviors. Glutamatergic mGluR5 receptors and matrix metalloproteinase-9 (MMP-9) are therapeutic targets to treat FXS, but clinical trials targeting each of these pathways have not been successful. Here, we tested if the electroencephalography (EEG) phenotypes associated with FXS are reversed with a novel combination of treatments affecting the two pathways. Fmr1 knockout (KO) mice were given 10 days of CTEP (mGluR5 antagonist) alone or in combination with minocycline (MMP-9 inhibitor). EEG was recorded during resting (no acoustic stimulation) and during sound presentations (to produce sound-evoked EEG) at 1 day and 10 days after the beginning of treatment administration to test acute effects and potential tachyphylaxis. In pre-treatment WT and KO mice comparisons, we replicated previously published Fmr1 KO mouse EEG phenotypes including elevated power in the resting gamma band, elevated single trial power, and reduced phase-locking to spectrotemporally dynamic auditory stimuli. We found that CTEP treatment alone did not show any benefit compared to vehicle in Fmr1 KO mice after either 1 or 10 days of treatment. CTEP + minocycline reduced resting gamma band power in the Fmr1 KO mice to a greater extent than vehicle at both treatment time points. There were no effects on sound-evoked responses. These data suggest that combined CTEP and minocycline treatment alters resting EEG measures while each treatment administered separately does not yield similar changes. High power in broadband gamma frequency correlates with irritability, stereotyped behaviors, and hyperactivity in FXS patients, suggesting a combination of drugs that reduce mGluR5 and MMP-9 activity may be beneficial in FXS.

The ability to pick out and attend to one sound in a noisy mixture underpins successful communication in many natural scenarios. Selective attention has been shown to drastically alter sound encoding in the cortex and has been hypothesized to modulate subcortical processing via an extensive efferent network. The body of work investigating this possibility in humans has not resulted in a clear consensus, possibly owing to limitations in the available methodologies. Here, we used new experimental tools that allowed distinct neural responses from across the auditory pathway to be simultaneously acquired from human listeners attending to the sound of one person talking while ignoring a second. Our series of experiments provide convergent evidence that selective attention does not influence sound encoding in the auditory periphery or brainstem, with an effect first appearing in the cortex. Humans’ ability to focus their attention on a single sound even in the presence of many others is as remarkable as it is essential. These findings add needed clarity regarding the mechanisms that make this feat possible.

Classical neuromodulators regulate arousal states, spanning deep sleep to vigilant wakefulness, primarily by activating cortical neurons. However, cortical astrocytes also express neuromodulatory G-protein-coupled receptors (GPCRs). While astrocytic noradrenergic receptors have been shown to modulate two critical regulators of arousal—cortical synchrony and extracellular adenosine levels—how other neuromodulatory signaling pathways similarly shape arousal remains unclear. Astrocytes in mammalian cortex express particularly high levels of the wake-promoting, Gq-coupled histamine-1-receptor (H1R), yet little is known about how astrocytic H1R contributes to regulation of arousal. To address this gap, we used pharmacological and genetic approaches in murine cortex to test how astrocyte-H1R signaling affects astrocyte calcium (Ca 2+ ), cortical neural activity across sleep/wake, and extracellular adenosine—an astrocytic output that regulates cortical arousal. Using ex vivo two-photon Ca 2+ imaging in acute cortical slices, we show that H1R mediates cell-autonomous astrocyte Ca 2+ responses to histamine (HA) and attenuates responses to norepinephrine (NE). Next, in vivo fiber photometry and electrophysiology results show that H1R deletion in cortical astrocytes disrupts local astrocyte Ca 2+ during wake and extracellular adenosine dynamics specifically around REM sleep transitions, when HA release is minimal. Further, astrocyte-specific H1R deletion in cortex promotes wakefulness and reduces REM sleep time. Our results indicate that H1R activity modulates astrocyte responses to non-histaminergic inputs by inducing lasting changes in astrocyte physiology that modulate extracellular adenosine and REM sleep. Our findings contribute to an emerging model in which neuromodulator GPCRs synergistically shape astrocyte physiology to regulate arousal behavior and adenosine signaling in the cortex.

Most spinal cord injuries (SCI) spare descending and sublesional circuits that can be targeted through motor cortex and spinal cord stimulation to mitigate locomotor deficits. However, the potential synergy between cortical and spinal stimulation remains unknown. Here, we first investigated the phase-locked electrical stimulation of the motor cortex and lumbar spinal cord at 40 Hz in a rat model of unilateral SCI. Combining cortical and lumbar stimulation around the anticipated lift synergistically enhanced leg movements. When integrated into rehabilitation training, cortical stimulation proved essential for the recovery of skilled locomotion. We next investigated the effects of high-frequency (330 Hz) lumbar and sacral stimulation combined with cortical stimulation. Timely integration during the swing phase showed that cortical and lumbar stimulations enhance the initial and mid-swing phases, while sacral stimulation improves extension velocity in the late swing. These findings indicate that supraspinal and sublesional neuromodulation offer complementary neuroprosthetic effects in targeted SCI gait rehabilitation.

Humans live in an environment that contains rich auditory stimuli, which must be processed efficiently. The entrainment of neural oscillations to acoustic inputs may support the processing of simple and complex sounds. However, the characteristics of this entrainment process have been shown to be inconsistent across species and experimental paradigms. It is imperative to establish whether neural activity in response to speech is a result of combination of simple evoked responses or of entrainment of neural oscillations in human participants. In this study, 12 participants with intracranial electrodes listened to natural speech and neural entrainment as evidenced by oscillatory activity persisting beyond the evoked responses was assessed. Neural activity was recorded from 165 contacts in Heschl's gyrus and superior temporal gyrus. First, acoustic edges in the speech envelope induced coherence between speech and auditory cortex activity. Further, entrainment in the theta-alpha band outlasted the acoustic stimulation. This activity exceeded what could be expected from a simple evoked response. These findings suggest that speech has the potential to entrain neural oscillations in the human auditory cortex.

Deep brain stimulation (DBS) of the globus pallidus internus (GPi) is an established treatment for dystonia, yet the neurophysiological mechanisms underlying frequency-dependent effects remain poorly understood. In this study, we investigate how different GPi-DBS frequencies modulate evoked potential (EP) characteristics within the basal ganglia-thalamo-cortical network in pediatric dystonia patients. We evaluated how increasing stimulation frequency alters EP morphology, focusing on peak-to-peak amplitude (PPa), peak-to-peak duration (PPd), and time to peak (TP). This analysis was motivated by clinical observations that higher DBS frequencies often produce distinct therapeutic effects, suggesting underlying differences in how neural circuits respond to varying stimulation rates. We analyzed intracranial electrophysiological recordings from 13 pediatric and young adult dystonia patients undergoing staged DBS implantation. EPs were recorded from the GPi and subthalamic nucleus (STN) of basal ganglia, and ventral oralis (VO) nucleus of the thalamus during unilateral GPi stimulation at 55, 85, 185, and 250 Hz. EP detection and characterization were performed using an automated algorithm, and group-level analyses were conducted using linear mixed effects models to assess frequency-dependent changes across regions. Increasing stimulation frequency significantly decreased PPa and increased PPd and TP, with a clear threshold effect: 55 Hz and 85 Hz produced similar responses, while 185 Hz and 250 Hz elicited significantly greater changes. These frequency-dependent effects were most pronounced in GPi recordings, followed by STN and VO, suggesting that local circuit dynamics are more sensitive to frequency modulation. Our findings highlight the distinct neurophysiological effects of DBS frequency on EP characteristics, emphasizing the need for personalized DBS programming. The pronounced frequency-dependent modulation observed in GPi suggests that optimal stimulation parameters should be tailored to the target region rather than applying uniform settings across patients. Future studies should investigate the clinical relevance of these EP dynamics and explore their potential as biomarkers for DBS optimization in dystonia.

The locus coeruleus–norepinephrine (LC-NE) system regulates arousal and awakening; however, it remains unclear whether the LC does this in a global or circuit-specific manner. We hypothesized that sensory-evoked awakenings are predominantly regulated by specific LC-NE efferent pathways. Anatomical, physiological, and functional modularities of LC-NE pathways involving the mouse basal forebrain (BF) and pontine reticular nucleus (PRN) were tested. We found partial anatomical segregation between the LC → PRN and LC → BF circuits. Extracellular NE dynamics in BF and PRN exhibited distinct sound-evoked activation during sleep, including a fast sound-evoked NE peak specific to PRN. Causal optogenetic interrogation of LC efferent pathways, by retro-channelrhodopsin (ChR2) activation or Platynereis dumerilii ciliary opsin (PdCO) silencing of synapses in target regions, revealed a role for early LC → PRN activity in driving arousal and sound-evoked awakenings. Together, our results uncover a role for early LC-NE PRN activity in connecting sensory and arousal pathways and establish LC heterogeneity in regulating arousal.

Target engagement determines therapeutic efficacy. In spinal cord stimulation (SCS), efficacy depends on the attributes of the electrodes used to deliver stimulation, particularly their position, interelectrode distance, size, and current orientation. We tested the effects of these electrode parameters using cervical stimulation to elicit forelimb muscle responses in the rat. We implanted devices over the C6 dorsal root entry zone (DREZ) in eight rats and measured responses in six forelimb muscles. We used custom designed electrode arrays to systematically vary position, distance, and size with linear arrays, and current orientation with circular arrays. Stimulation consisted of biphasic and pseudomonophasic pulse shapes with bipolar or distant return, and a high-definition montage with four returns surrounding a central contact to increase local current density. Efficacy was calculated from the motor thresholds of recruitment curves, and parameters were compared using linear mixed models. For position, stimulation over the DREZ was most effective, reducing thresholds by 25.9% ( p = 0.0002) relative to the midline; efficacy decreased as the electrode was positioned medial or lateral to the DREZ. For distance, placing the electrodes farther apart significantly improved efficacy ( p = 0.0022). For size, large electrodes increased SCS efficacy, reducing thresholds by 21.5% ( p = 0.0026) relative to small electrodes. After accounting for position and distance, current orientation did not affect SCS efficacy. Lastly, the high-definition montage decreased efficacy, increasing thresholds by 16.7% ( p = 0.003) relative to monopolar stimulation with a distant return. In conclusion, electrode position, distance, and size had the greatest effect on SCS efficacy, with the optimal parameters combining large electrodes at the DREZ position with a distant return. These results have the potential to lower the current needed to engage cervical spinal circuitry and to inform the design of SCS systems to improve dexterity in people with neurological injury or disease.