Publications by authors named "Charles Y Liu"

134 Publications

Amygdaloid theta-band power increases during conflict processing in humans.

J Clin Neurosci 2021 Sep 14;91:183-192. Epub 2021 Jul 14.

Department of Neurological Surgery, Keck School of Medicine of USC, University of Southern California, Los Angeles, CA, United States; USC Neurorestoration Center, Keck School of Medicine of USC, Los Angeles, CA, United States; University of Southern California, Los Angeles, CA, United States; Department of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, United States.

The amygdala is a medial temporal lobe structure known to be involved in processing emotional conflict. However, its role in processing non-emotional conflict is not well understood. Previous studies have utilized the Stroop Task to examine brain modulation of humans under the color-word conflict scenario, which is non-emotional conflict processing, and found hippocampal theta-band (4-7 Hz) modulation. This study aims to survey amygdaloid theta power changes during non-emotional conflict processing using intracranial depth electrodes in nine epileptic patients (3 female; age 20-62). All patients were asked to perform a modified Stroop task. During task performance, local field potential (LFP) data was recorded from macro contacts sampled at 2 K Hz and used for analysis. Mean theta power change from baseline was compared between the incongruent and congruent task condition groups using a paired sample t-test. Seven patients were available for analysis after artifact exclusion. In five out of seven patients, statistically significant increases in theta-band power from baseline were noted during the incongruent task condition (paired sample t-test p < 0.001), including one patient exhibiting theta power increases in both task conditions. Average response time was 1.07 s (failure trials) and 1.04 s (success trials). No speed-accuracy tradeoff was noted in this analysis. These findings indicate that human amygdaloid theta-band modulation may play a role in processing non-emotional conflict. It builds directly upon work suggesting that the amygdala processes emotional conflict and provides a neurophysiological mechanism for non-emotional conflict processing as well.
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http://dx.doi.org/10.1016/j.jocn.2021.07.001DOI Listing
September 2021

Neuropathological effects of chronically implanted, intracortical microelectrodes in a tetraplegic patient.

J Neural Eng 2021 07 27;18(4). Epub 2021 Jul 27.

Department of Pathology, Keck USC School of Medicine, Los Angeles, CA, United States of America.

Intracortical microelectrode arrays (MEA) can be used as part of a brain-machine interface system to provide sensory feedback control of an artificial limb to assist persons with tetraplegia. Variability in functionality of electrodes has been reported but few studies in humans have examined the impact of chronic brain tissue responses revealed postmortem on electrode performanceIn a tetraplegic man, recording MEAs were implanted into the anterior intraparietal area and Brodmann's area 5 (BA5) of the posterior parietal cortex and a recording and stimulation array was implanted in BA1 of the primary somatosensory cortex (S1). The participant expired from unrelated causes seven months after MEA implantation. The underlying tissue of two of the three devices was processed for histology and electrophysiological recordings were assessed.Recordings of neuronal activity were obtained from all three MEAs despite meningeal encapsulation. However, the S1 array had a greater encapsulation, yielded lower signal quality than the other arrays and failed to elicit somatosensory percepts with electrical stimulation. Histological examination of tissues underlying S1 and BA5 implant sites revealed localized leptomeningeal proliferation and fibrosis, lymphocytic infiltrates, astrogliosis, and foreign body reaction around the electrodes. The BA5 recording site showed focal cerebral microhemorrhages and leptomeningeal vascular ectasia. The S1 site showed focal tissue damage including vascular recanalization, neuronal loss, and extensive subcortical white matter necrosis. The tissue response at the S1 site included hemorrhagic-induced injury suggesting a likely mechanism for reduced function of the S1 implant.Our findings are similar to those from animal studies with chronic intracortical implants and suggest that vascular disruption and microhemorrhage during device implantation are important contributors to overall array and individual electrode performance and should be a topic for future device development to mitigate tissue responses. Neurosurgical considerations are also discussed.
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http://dx.doi.org/10.1088/1741-2552/ac127eDOI Listing
July 2021

Safety of direct injection of oligodendrocyte progenitor cells into the spinal cord of uninjured Göttingen minipigs.

J Neurosurg Spine 2021 Jul 9:1-9. Epub 2021 Jul 9.

4Asterias Biotherapeutics, a wholly owned subsidiary of Lineage Cell Therapeutics, Carlsbad, California.

Objective: This study was conducted as a final proof-of-safety direct injection of oligodendrocyte progenitor cells into the uninjured spinal cord prior to translation to the human clinical trials.

Methods: In this study, 107 oligodendrocyte progenitor cells (LCTOPC1, also known as AST-OPC1 and GRNOPC1) in 50-μL suspension were injected directly into the uninjured spinal cords of 8 immunosuppressed Göttingen minipigs using a specially designed stereotactic delivery device. Four additional Göttingen minipigs were given Hanks' Balanced Salt Solution and acted as the control group.

Results: Cell survival and no evidence of histological damage, abnormal inflammation, microbiological or immunological abnormalities, tumor formation, or unexpected morbidity or mortality were demonstrated.

Conclusions: These data strongly support the safety of intraparenchymal injection of LCTOPC1 into the spinal cord using a model anatomically similar to that of the human spinal cord. Furthermore, this research provides guidance for future clinical interventions, including mechanisms for precise positioning and anticipated volumes of biological payloads that can be safely delivered directly into uninjured portions of the spinal cord.
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http://dx.doi.org/10.3171/2020.12.SPINE201853DOI Listing
July 2021

Neuromodulation in Beta-Band Power Between Movement Execution and Inhibition in the Human Hippocampus.

Neuromodulation 2021 Jul 5. Epub 2021 Jul 5.

Department of Neurological Surgery, Keck School of Medicine of USC, University of Southern California, Los Angeles, CA, USA.

Introduction: The hippocampus is thought to be involved in movement, but its precise role in movement execution and inhibition has not been well studied. Previous work with direct neural recordings has found beta-band (13-30 Hz) modulation in both movement execution and inhibition throughout the motor system, but the role of beta-band modulation in the hippocampus during movement inhibition is not well understood. Here, we perform a Go/No-Go reaching task in ten patients with medically refractory epilepsy to study human hippocampal beta-power changes during movement.

Materials And Methods: Ten epilepsy patients (5 female; ages 21-46) were implanted with intracranial depth electrodes for seizure monitoring and localization. Local field potentials were sampled at 2000 Hz during a Go/No-Go movement task. Comparison of beta-band power between Go and No-Go conditions was conducted using Wilcoxon signed-rank hypothesis testing for each patient. Sub-analyses were conducted to assess differences in the anterior vs. posterior contacts, ipsilateral vs. contralateral contacts, and male vs. female beta power values.

Results: Eight out of ten patients showed significant beta-power decreases during the Go movement response (p < 0.05) compared to baseline. Eight out of ten patients also showed significant beta power increases in the No-Go condition, occurring in the absence of movement. No significant differences were noted between ipsilateral vs. contralateral contacts, nor in anterior vs. posterior hippocampal contacts. Female participants had a higher task success rate than males and had significantly greater beta-power increases in the No-Go condition (p < 0.001).

Conclusion: These findings indicate that increases in hippocampal beta power are associated with movement inhibition. To the best of our knowledge, this study is the first to report this phenomenon in the human hippocampus. The beta band may represent a state-change signal involved in motor processing. Future focus on the beta band in understanding human motor and impulse control will be vital.
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http://dx.doi.org/10.1111/ner.13486DOI Listing
July 2021

Massively parallel functional photoacoustic computed tomography of the human brain.

Nat Biomed Eng 2021 May 31. Epub 2021 May 31.

Caltech Optical Imaging Laboratory, Andrew and Peggy Cherng Department of Medical Engineering, California Institute of Technology, Pasadena, CA, USA.

Blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging of the human brain requires bulky equipment for the generation of magnetic fields. Photoacoustic computed tomography obviates the need for magnetic fields by using light and sound to measure deoxyhaemoglobin and oxyhaemoglobin concentrations to then quantify oxygen saturation and blood volumes. Yet, the available imaging speeds, fields of view (FOV), sensitivities and penetration depths have been insufficient for functional imaging of the human brain. Here, we show that massively parallel ultrasonic transducers arranged hemispherically around the human head can produce tomographic images of the brain with a 10-cm-diameter FOV and spatial and temporal resolutions of 350 µm and 2 s, respectively. In patients who had a hemicraniectomy, a comparison of functional photoacoustic computed tomography and 7 T BOLD functional magnetic resonance imaging showed a strong spatial correspondence in the same FOV and a high temporal correlation between BOLD signals and photoacoustic signals, with the latter enabling faster detection of functional activation. Our findings establish the use of photoacoustic computed tomography for human brain imaging.
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http://dx.doi.org/10.1038/s41551-021-00735-8DOI Listing
May 2021

Vagus nerve stimulation paired with rehabilitation for upper limb motor function after ischaemic stroke (VNS-REHAB): a randomised, blinded, pivotal, device trial.

Lancet 2021 Apr;397(10284):1545-1553

Department of Neurology, Center for Neurotechnology and Neurorecovery, Massachusetts General Hospital, Harvard Medical School, Boston, MA, USA; Department of Physical Therapy, MGH Institute of Health Professions, Boston, MA, USA.

Background: Long-term loss of arm function after ischaemic stroke is common and might be improved by vagus nerve stimulation paired with rehabilitation. We aimed to determine whether this strategy is a safe and effective treatment for improving arm function after stroke.

Methods: In this pivotal, randomised, triple-blind, sham-controlled trial, done in 19 stroke rehabilitation services in the UK and the USA, participants with moderate-to-severe arm weakness, at least 9 months after ischaemic stroke, were randomly assigned (1:1) to either rehabilitation paired with active vagus nerve stimulation (VNS group) or rehabilitation paired with sham stimulation (control group). Randomisation was done by ResearchPoint Global (Austin, TX, USA) using SAS PROC PLAN (SAS Institute Software, Cary, NC, USA), with stratification by region (USA vs UK), age (≤30 years vs >30 years), and baseline Fugl-Meyer Assessment-Upper Extremity (FMA-UE) score (20-35 vs 36-50). Participants, outcomes assessors, and treating therapists were masked to group assignment. All participants were implanted with a vagus nerve stimulation device. The VNS group received 0·8 mA, 100 μs, 30 Hz stimulation pulses, lasting 0·5 s. The control group received 0 mA pulses. Participants received 6 weeks of in-clinic therapy (three times per week; total of 18 sessions) followed by a home exercise programme. The primary outcome was the change in impairment measured by the FMA-UE score on the first day after completion of in-clinic therapy. FMA-UE response rates were also assessed at 90 days after in-clinic therapy (secondary endpoint). All analyses were by intention to treat. This trial is registered at ClinicalTrials.gov, NCT03131960.

Findings: Between Oct 2, 2017, and Sept 12, 2019, 108 participants were randomly assigned to treatment (53 to the VNS group and 55 to the control group). 106 completed the study (one patient for each group did not complete the study). On the first day after completion of in-clinic therapy, the mean FMA-UE score increased by 5·0 points (SD 4·4) in the VNS group and by 2·4 points (3·8) in the control group (between group difference 2·6, 95% CI 1·0-4·2, p=0·0014). 90 days after in-clinic therapy, a clinically meaningful response on the FMA-UE score was achieved in 23 (47%) of 53 patients in the VNS group versus 13 (24%) of 55 patients in the control group (between group difference 24%, 6-41; p=0·0098). There was one serious adverse event related to surgery (vocal cord paresis) in the control group.

Interpretation: Vagus nerve stimulation paired with rehabilitation is a novel potential treatment option for people with long-term moderate-to-severe arm impairment after ischaemic stroke.

Funding: MicroTransponder.
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http://dx.doi.org/10.1016/S0140-6736(21)00475-XDOI Listing
April 2021

Hippocampal and Orbitofrontal Theta Band Coherence Diminishes During Conflict Resolution.

World Neurosurg 2021 Aug 16;152:e32-e44. Epub 2021 Apr 16.

Department of Neurological Surgery, Keck School of Medicine of USC, University of Southern California, Los Angeles, California, USA; USC Neurorestoration Center, Keck School of Medicine of USC, University of Southern California, Los Angeles, California, USA; Department of Biology and Biological Engineering, California Institute of Technology, Pasadena, California, USA.

Objective: Coherence between the hippocampus and other brain structures has been shown with the theta frequency (3-8 Hz). Cortical decreases in theta coherence are believed to reflect response accuracy efficiency. However, the role of theta coherence during conflict resolution is poorly understood in noncortical areas. In this study, coherence between the hippocampus and orbitofrontal cortex (OFC) was measured during a conflict resolution task. Although both brain areas have been previously implicated in the Stroop task, their interactions are not well understood.

Methods: Nine patients were implanted with stereotactic electroencephalography contacts in the hippocampus and OFC. Local field potential data were sampled throughout discrete phases of a Stroop task. Coherence was calculated for hippocampal and OFC contact pairs, and coherence spectrograms were constructed for congruent and incongruent conditions. Coherence changes during cue processing were identified using a nonparametric cluster-permutation t test. Group analysis was conducted to compare overall theta coherence changes among conditions.

Results: In 6 of 9 patients, decreased theta coherence was observed only during the incongruent condition (P < 0.05). Congruent theta coherence did not change from baseline. Group analysis showed lower theta coherence for the incongruent condition compared with the congruent condition (P < 0.05).

Conclusions: Theta coherence between the hippocampus and OFC decreased during conflict. This finding supports existing theories that theta coherence desynchronization contributes to improved response accuracy and processing efficiency during conflict resolution. The underlying theta coherence observed between the hippocampus and OFC during conflict may be distinct from its previously observed role in memory.
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http://dx.doi.org/10.1016/j.wneu.2021.04.023DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8338769PMC
August 2021

Electromyogram (EMG) Removal by Adding Sources of EMG (ERASE)-A Novel ICA-Based Algorithm for Removing Myoelectric Artifacts From EEG.

Front Neurosci 2020 15;14:597941. Epub 2021 Jan 15.

Department of Neurology, University of California, Irvine, Irvine, CA, United States.

Electroencephalographic (EEG) recordings are often contaminated by electromyographic (EMG) artifacts, especially when recording during movement. Existing methods to remove EMG artifacts include independent component analysis (ICA), and other high-order statistical methods. However, these methods can not effectively remove most of EMG artifacts. Here, we proposed a modified ICA model for EMG artifacts removal in the EEG, which is called EMG Removal by Adding Sources of EMG (ERASE). In this new approach, additional channels of real EMG from neck and head muscles (reference artifacts) were added as inputs to ICA in order to "force" the most power from EMG artifacts into a few independent components (ICs). The ICs containing EMG artifacts (the "artifact ICs") were identified and rejected using an automated procedure. ERASE was validated first using both simulated and experimentally-recorded EEG and EMG. Simulation results showed ERASE removed EMG artifacts from EEG significantly more effectively than conventional ICA. Also, it had a low false positive rate and high sensitivity. Subsequently, EEG was collected from 8 healthy participants while they moved their hands to test the realistic efficacy of this approach. Results showed that ERASE successfully removed EMG artifacts (on average, about 75% of EMG artifacts were removed when using real EMGs as reference artifacts) while preserving the expected EEG features related to movement. We also tested the ERASE procedure using simulated EMGs as reference artifacts (about 63% of EMG artifacts removed). Compared to conventional ICA, ERASE removed on average 26% more EMG artifacts from EEG. These findings suggest that ERASE can achieve significant separation of EEG signal and EMG artifacts without a loss of the underlying EEG features. These results indicate that using additional real or simulated EMG sources can increase the effectiveness of ICA in removing EMG artifacts from EEG. Combined with automated artifact IC rejection, ERASE also minimizes potential user bias. Future work will focus on improving ERASE so that it can also be used in real-time applications.
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http://dx.doi.org/10.3389/fnins.2020.597941DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7873899PMC
January 2021

Gray Matter Atrophy: The Impacts of Resective Surgery and Vagus Nerve Stimulation in Drug-Resistant Epilepsy.

World Neurosurg 2021 05 4;149:e535-e545. Epub 2021 Feb 4.

USC Neurorestoration Center, Keck School of Medicine of the University of Southern California, Los Angeles, California, USA. Electronic address:

Background: There is great concern for cognitive function after resective temporal lobe surgery for drug-resistant epilepsy. However, few studies have investigated postoperative anatomical changes, and the downstream effects of surgery are poorly understood. This study investigated volumetric changes after resective surgery and vagus nerve stimulation (VNS) for epilepsy.

Methods: Preoperative and latest postoperative (mean, 28 months) structural T1 magnetic resonance imaging scans were retrospectively obtained for 43 patients: 27 temporal lobe resections (TLRs), 6 extratemporal lobe resections, and 10 VNS, undergoing surgery for drug-resistant epilepsy between 2012 and 2017. Automated volumetric analyses of predefined cortical gray matter and subcortical structures were performed. Preoperative and postoperative volumes were compared, and the effects of age, gender, operation type, resection laterality, selectivity, time since surgery, and seizure outcome on volumetric changes were analyzed.

Results: After TLRs, there were reductions in contralateral hemispheric gray matter, temporal lobe, entorhinal cortex, parahippocampal, superior temporal, middle temporal, inferior temporal (P = 0.02), lingual, fusiform, precentral, paracentral, postcentral, pericalcarine gyri, and ipsilateral superior parietal gyrus. After VNS, there was bilateral atrophy in the thalamus, putamen, cerebellum, rostral anterior cingulate, posterior cingulate, medial orbitofrontal, paracentral, fusiform, and transverse temporal gyri. There was a significant effect of surgery type but no effect of age, gender, operation type, resection laterality, selectivity, time since surgery, and seizure outcome on contralateral hippocampal gray matter change.

Conclusion: This is the first study to demonstrate volumetric decreases in temporal and connected regions after TLRs and VNS. These results provide interesting insight into functional network changes.
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http://dx.doi.org/10.1016/j.wneu.2021.01.141DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8121141PMC
May 2021

A sparse multiscale nonlinear autoregressive model for seizure prediction.

J Neural Eng 2021 02 26;18(2). Epub 2021 Feb 26.

Department of Biomedical Engineering, University of Southern California, Los Angeles, CA 90089, United States of America.

Accurate seizure prediction is highly desirable for medical interventions such as responsive electrical stimulation. We aim to develop a classification model that can predict seizures by identifying preictal states, i.e. the precursor of a seizure, based on multi-channel intracranial electroencephalography (iEEG) signals.A two-level sparse multiscale classification model was developed to classify interictal and preictal states from iEEG data. In the first level, short time-scale linear dynamical features were extracted as autoregressive (AR) model coefficients; arbitrary (usually long) time-scale linear and nonlinear dynamical features were extracted as Laguerre-Volterra AR model coefficients; root-mean-square error of model prediction was used as a feature representing model unpredictability. In the second level, all features were fed into a sparse classifier to discriminate the iEEG data between interictal and preictal states.. The two-level model can accurately classify seizure states using iEEG data recorded from ten canine and human subjects. Adding arbitrary (usually long) time-scale and nonlinear features significantly improves model performance compared with the conventional AR modeling approach. There is a high degree of variability in the types of features contributing to seizure prediction across different subjects.. This study suggests that seizure generation may involve distinct linear/nonlinear dynamical processes caused by different underlying neurobiological mechanisms. It is necessary to build patient-specific classification models with a wide range of dynamical features.
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http://dx.doi.org/10.1088/1741-2552/abdd43DOI Listing
February 2021

Cognitive effects of theta frequency bilateral subthalamic nucleus stimulation in Parkinson's disease: A pilot study.

Brain Stimul 2021 Mar-Apr;14(2):230-240. Epub 2021 Jan 6.

Department of Neurological Surgery, Keck School of Medicine of USC, Los Angeles, United States; USC Neurorestoration Center, Keck School of Medicine of USC, Los Angeles, United States. Electronic address:

Background: There is significant evidence for cognitive decline following deep brain stimulation (DBS). Current stimulation paradigms utilize gamma frequency stimulation for optimal motor benefits; however, little has been done to optimize stimulation parameters for cognition. Recent evidence implicates subthalamic nucleus (STN) theta oscillations in executive function, and theta oscillations are well-known to relate to episodic memory, suggesting that theta frequency stimulation could potentially improve cognition in Parkinson's disease (PD).

Objective: To evaluate the acute effects of theta frequency bilateral STN stimulation on executive function in PD versus gamma frequency and off, as well as investigate the differential effects on episodic versus nonepisodic verbal fluency.

Methods: Twelve patients (all males, mean age 60.8) with bilateral STN DBS for PD underwent a double-blinded, randomized cognitive testing during stimulation at (1) 130-135 Hz (gamma), (2) 10 Hz (theta) and (3) off. Executive functions and processing speed were evaluated using verbal fluency tasks (letter, episodic category, nonepisodic category, and category switching), color-word interference task, and random number generation task. Performance at each stimulation frequency was compared within subjects.

Results: Theta frequency significantly improved episodic category fluency compared to gamma, but not compared to off. There were no significant differences between stimulation frequencies in other tests.

Conclusion: In this pilot trial, our results corroborate the role of theta oscillations in episodic retrieval, although it is unclear whether this reflects direct modulation of the medial temporal lobe and whether similar effects can be found with more canonical memory paradigms. Further work is necessary to corroborate our findings and investigate the possibility of interleaving theta and gamma frequency stimulation for concomitant motor and cognitive effects.
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http://dx.doi.org/10.1016/j.brs.2020.12.014DOI Listing
January 2021

Deep Brain Stimulation for Alzheimer's Disease: Tackling Circuit Dysfunction.

Neuromodulation 2021 Feb 30;24(2):171-186. Epub 2020 Dec 30.

USC Neurorestoration Center, Keck School of Medicine of USC, Los Angeles, CA, 90033, USA.

Objectives: Treatments for Alzheimer's disease are urgently needed given its enormous human and economic costs and disappointing results of clinical trials targeting the primary amyloid and tau pathology. On the other hand, deep brain stimulation (DBS) has demonstrated success in other neurological and psychiatric disorders leading to great interest in DBS as a treatment for Alzheimer's disease.

Materials And Methods: We review the literature on 1) circuit dysfunction in Alzheimer's disease and 2) DBS for Alzheimer's disease. Human and animal studies are reviewed individually.

Results: There is accumulating evidence of neural circuit dysfunction at the structural, functional, electrophysiological, and neurotransmitter level. Recent evidence from humans and animals indicate that DBS has the potential to restore circuit dysfunction in Alzheimer's disease, similarly to other movement and psychiatric disorders, and may even slow or reverse the underlying disease pathophysiology.

Conclusions: DBS is an intriguing potential treatment for Alzheimer's disease, targeting circuit dysfunction as a novel therapeutic target. However, further exploration of the basic disease pathology and underlying mechanisms of DBS is necessary to better understand how circuit dysfunction can be restored. Additionally, robust clinical data in the form of ongoing phase III clinical trials are needed to validate the efficacy of DBS as a viable treatment.
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http://dx.doi.org/10.1111/ner.13305DOI Listing
February 2021

Refinement of High-Gamma EEG Features From TBI Patients With Hemicraniectomy Using an ICA Informed by Simulated Myoelectric Artifacts.

Front Neurosci 2020 24;14:599010. Epub 2020 Nov 24.

Department of Neurology, University of California, Irvine, Irvine, CA, United States.

Recent studies have shown the ability to record high-γ signals (80-160 Hz) in electroencephalogram (EEG) from traumatic brain injury (TBI) patients who have had hemicraniectomies. However, extraction of the movement-related high-γ remains challenging due to a confounding bandwidth overlap with surface electromyogram (EMG) artifacts related to facial and head movements. In our previous work, we described an augmented independent component analysis (ICA) approach for removal of EMG artifacts from EEG, and referred to as . Here, we tested this algorithm on EEG recorded from six TBI patients with hemicraniectomies while they performed a thumb flexion task. ERASE removed a mean of 52 ± 12% (mean ± S.E.M) (maximum 73%) of EMG artifacts. In contrast, conventional ICA removed a mean of 27 ± 19% (mean ± S.E.M) of EMG artifacts from EEG. In particular, high-γ synchronization was significantly improved in the contralateral hand motor cortex area within the hemicraniectomy site after ERASE was applied. A more sophisticated measure of high-γ complexity is the fractal dimension (FD). Here, we computed the FD of EEG high-γ on each channel. Relative FD of high-γ was defined as that the FD in move state was subtracted by FD in idle state. We found relative FD of high-γ over hemicraniectomy after applying ERASE were strongly correlated to the amplitude of finger flexion force. Results showed that significant correlation coefficients across the electrodes related to thumb flexion averaged ~0.76, while the coefficients across the homologous electrodes in non-hemicraniectomy areas were nearly 0. After conventional ICA, a correlation between relative FD of high-γ and force remained high in both hemicraniectomy areas (up to 0.86) and non-hemicraniectomy areas (up to 0.81). Across all subjects, an average of 83% of electrodes significantly correlated with force was located in the hemicraniectomy areas after applying ERASE. After conventional ICA, only 19% of electrodes with significant correlations were located in the hemicraniectomy. These results indicated that the new approach isolated electrophysiological features during finger motor activation while selectively removing confounding EMG artifacts. This approach removed EMG artifacts that can contaminate high-gamma activity recorded over the hemicraniectomy.
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http://dx.doi.org/10.3389/fnins.2020.599010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7732541PMC
November 2020

Pre-whitening and Null Projection as an Artifact Suppression Method for Electrocorticography Stimulation in Bi-Directional Brain Computer Interfaces.

Annu Int Conf IEEE Eng Med Biol Soc 2020 07;2020:3493-3496

Electrocorticography (ECoG)-based bi-directional (BD) brain-computer interfaces (BCIs) are a forthcoming technology promising to help restore function to those with motor and sensory deficits. A major problem with this paradigm is that the cortical stimulation necessary to elicit artificial sensation creates strong electrical artifacts that can disrupt BCI operation by saturating recording amplifiers or obscuring useful neural signal. Even with state-of-the-art hardware artifact suppression methods, robust signal processing techniques are still required to suppress residual artifacts that are present at the digital back-end. Herein we demonstrate the effectiveness of a pre-whitening and null projection artifact suppression method using ECoG data recorded during a clinical neurostimulation procedure. Our method achieved a maximum artifact suppression of 21.49 dB and significantly increased the number of artifact-free frequencies in the frequency domain. This performance surpasses that of a more traditional independent component analysis methodology, while retaining a reduced complexity and increased computational efficiency.
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http://dx.doi.org/10.1109/EMBC44109.2020.9175760DOI Listing
July 2020

A Prototype of a Fully-Implantable Charge-Balanced Artificial Sensory Stimulator for Bi-directional Brain-Computer-Interface (BD-BCI).

Annu Int Conf IEEE Eng Med Biol Soc 2020 07;2020:3083-3085

Bi-directional brain-computer interfaces (BD-BCI) to restore movement and sensation must achieve concurrent operation of recording and decoding of motor commands from the brain and stimulating the brain with somatosensory feedback. Previously we developed and validated a benchtop prototype of a fully implantable BCI system for motor decoding. Here, a prototype artificial sensory stimulator was integrated into the benchtop system to develop a prototype of a fully-implantable BD-BCI. The artificial sensory stimulator incorporates an active charge balancing mechanism based on pulse-width modulation to ensure safe stimulation for chronically interfaced electrodes to prevent damage to brain tissue and electrodes. The feasibility of the BD-BCI system's active charge balancing was tested in phantom brain tissue. With the charge-balancing, the removal of the residual charges on an electrode was evident. This is a critical milestone toward fully-implantable BD-BCI systems.
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http://dx.doi.org/10.1109/EMBC44109.2020.9176718DOI Listing
July 2020

Thermal Analysis of a Skull Implant in Brain-Computer Interfaces.

Annu Int Conf IEEE Eng Med Biol Soc 2020 07;2020:3066-3069

The goal of this study is to estimate the thermal impact of a titanium skull unit (SU) implanted on the exterior aspect of the human skull. We envision this unit to house the front-end of a fully implantable electrocorticogram (ECoG)-based bi-directional (BD) brain-computer interface (BCI). Starting from the bio-heat transfer equation with physiologically and anatomically constrained tissue parameters, we used the finite element method (FEM) implemented in COMSOL to build a computational model of the SU's thermal impact. Based on our simulations, we predicted that the SU could consume up to 75 mW of power without raising the temperature of surrounding tissues above the safe limits (increase in temperature of 1°C). This power budget by far exceeds the power consumption of our front-end prototypes, suggesting that this design can sustain the SU's ability to record ECoG signals and deliver cortical stimulation. These predictions will be used to further refine the existing SU design and inform the design of future SU prototypes.
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http://dx.doi.org/10.1109/EMBC44109.2020.9175483DOI Listing
July 2020

The effect of stroke on micturition associated brain activity: A pilot fMRI study.

Neurourol Urodyn 2020 11 6;39(8):2198-2205. Epub 2020 Aug 6.

Stevens Neuroimaging and Informatics Institute, Keck School of Medicine of University of Southern California, Los Angeles, California.

Objective: Cerebral stroke is a unique model for studying the role of the brain in lower urinary tract (LUT) control. By its nature, stroke must change the activity of the brain to cause LUT dysfunction. The objective of this study was to describe changes in micturition-related brain activity in patients who develop LUT symptoms (LUTS) after a cerebral stroke.

Materials And Methods: Healthy controls (HC, n = 10) and patients who developed storage LUTS after a cerebral stroke (n = 7) were recruited. Functional magnetic resonance imaging was used to assess brain activity in each subject. In the task-based block design, blood-oxygen-level-dependent (BOLD) signal was detected during rest, active bladder filling, and bladder voiding. BOLD signal intensity was compared between HCs and stroke subjects during bladder filling, voiding, and voiding initiation.

Results: Stroke subjects exhibited higher activity in the periaqueductal gray and cerebellum during bladder filling and bladder voiding. HCs exhibited more intense activity in higher centers, such as the cingulate cortex, motor cortex, and the dorsolateral prefrontal cortex in each of the phases examined.

Conclusions: Subjects with stroke-related LUTS exhibit a specific pattern of brain activity during bladder filling and voiding. There appears to be a greater reliance on primitive centers (cerebellum, midbrain) than in healthy controls during both phases of the micturition cycle. We hypothesize that these findings may reflect loss of connectivity with higher brain centers after a stroke.
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http://dx.doi.org/10.1002/nau.24473DOI Listing
November 2020

Nine-year prospective efficacy and safety of brain-responsive neurostimulation for focal epilepsy.

Neurology 2020 09 20;95(9):e1244-e1256. Epub 2020 Jul 20.

From the Cleveland Clinic Foundation (D.R.N., A.V.A.), OH; California Pacific Medical Center (K.D.L., P.B.W.), San Francisco; Augusta University (A.M.M., Y.D.P.), GA; Henry Ford Hospital (G.L.B.), Detroit, MI; Ohio Health Neuroscience (B.J.S.), Columbus; Swedish Neuroscience Institute (R.P.G., M.J.D.), Seattle, WA; Mayo Clinic Arizona (K.H.N., R.S.Z.), Scottsdale; Johns Hopkins Medicine (G.K.B., W.S.A.), Baltimore, MD; Keck School of Medicine of USC (C.H., C.Y.L.), Los Angeles, CA; Via Christi Epilepsy Center (R.W.L., T.S.), Wichita, KS; Yale University School of Medicine (R.B.D., L.J.H.), New Haven, CT; Mayo Clinic Florida (R.E.W., W.T.), Jacksonville; Columbia University Medical Center (S.S., G.M.M.), New York, NY; University of Texas Southwestern Medical Center (M.A.A.), Dallas; Geisel School of Medicine at Dartmouth (B.C.J., D.W.R.), Hanover, NH; Indiana University School of Medicine (V.S., T.C.W.), Indianapolis; Massachusetts General Hospital (S.S.C., A.J.C.), Boston; Mayo Clinic Minnesota (G.A.W., B.N.L.), Rochester; Medical University of South Carolina (J.C.E., J.J.H.), Charleston; Oregon Health & Science University (D.C. Spencer, L.E.), Portland; Thomas Jefferson University (C.T.S., M.R.S.), Philadelphia, PA; Nicklaus Children's Hospital (I.M.), Miami, FL; Saint Barnabas Medical Center (E.B.G.), Livingston, NJ; University of Rochester Medical Center (M.J.B., A.J.F.), NY; University of Wisconsin Hospital and Clinics (P.R.), Madison; Baylor College of Medicine (A.M.G., E.M.M.), Houston, TX; Emory University School of Medicine (R.E.G.), Atlanta, GA; George Washington University School of Medicine and Health Sciences (D.C. Shields), Washington, DC; Weill Cornell Medical College (T.H.S., D.R.L.), New York, NY; University of Virginia School of Medicine (N.B.F., W.J.E.), Charlottesville; Louisiana State University Health Sciences Center (P.W.O., N.R.V.-P.), New Orleans; University of Florida (S.E., S.N.R.), Gainesville; Wake Forest University Health Sciences (J.G.B.), Winston-Salem, NC; NeuroPace, Inc (T.A.C., F.T.S., C.G.S., K.L.M., T.L.S., M.J.M.), Mountain View; and Stanford University (M.J.M.), Palo Alto, CA.

Objective: To prospectively evaluate safety and efficacy of brain-responsive neurostimulation in adults with medically intractable focal onset seizures (FOS) over 9 years.

Methods: Adults treated with brain-responsive neurostimulation in 2-year feasibility or randomized controlled trials were enrolled in a long-term prospective open label trial (LTT) to assess safety, efficacy, and quality of life (QOL) over an additional 7 years. Safety was assessed as adverse events (AEs), efficacy as median percent change in seizure frequency and responder rate, and QOL with the Quality of Life in Epilepsy (QOLIE-89) inventory.

Results: Of 256 patients treated in the initial trials, 230 participated in the LTT. At 9 years, the median percent reduction in seizure frequency was 75% ( < 0.0001, Wilcoxon signed rank), responder rate was 73%, and 35% had a ≥90% reduction in seizure frequency. We found that 18.4% (47 of 256) experienced ≥1 year of seizure freedom, with 62% (29 of 47) seizure-free at the last follow-up and an average seizure-free period of 3.2 years (range 1.04-9.6 years). Overall QOL and epilepsy-targeted and cognitive domains of QOLIE-89 remained significantly improved ( < 0.05). There were no serious AEs related to stimulation, and the sudden unexplained death in epilepsy (SUDEP) rate was significantly lower than predefined comparators ( < 0.05, 1-tailed χ).

Conclusions: Adjunctive brain-responsive neurostimulation provides significant and sustained reductions in the frequency of FOS with improved QOL. Stimulation was well tolerated; implantation-related AEs were typical of other neurostimulation devices; and SUDEP rates were low.

Clinicaltrialsgov Identifier: NCT00572195.

Classification Of Evidence: This study provides Class IV evidence that brain-responsive neurostimulation significantly reduces focal seizures with acceptable safety over 9 years.
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http://dx.doi.org/10.1212/WNL.0000000000010154DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7538230PMC
September 2020

Gamma-band modulation in the human amygdala during reaching movements.

Neurosurg Focus 2020 07;49(1):E4

Departments of1Neurological Surgery and.

Objective: Motor brain-computer interface (BCI) represents a new frontier in neurological surgery that could provide significant benefits for patients living with motor deficits. Both the primary motor cortex and posterior parietal cortex have successfully been used as a neural source for human motor BCI, leading to interest in exploring other brain areas involved in motor control. The amygdala is one area that has been shown to have functional connectivity to the motor system; however, its role in movement execution is not well studied. Gamma oscillations (30-200 Hz) are known to be prokinetic in the human cortex, but their role is poorly understood in subcortical structures. Here, the authors use direct electrophysiological recordings and the classic "center-out" direct-reach experiment to study amygdaloid gamma-band modulation in 8 patients with medically refractory epilepsy.

Methods: The study population consisted of 8 epilepsy patients (2 men; age range 21-62 years) who underwent implantation of micro-macro depth electrodes for seizure localization and EEG monitoring. Data from the macro contacts sampled at 2000 Hz were used for analysis. The classic center-out direct-reach experiment was used, which consists of an intertrial interval phase, a fixation phase, and a response phase. The authors assessed the statistical significance of neural modulation by inspecting for nonoverlapping areas in the 95% confidence intervals of spectral power for the response and fixation phases.

Results: In 5 of the 8 patients, power spectral analysis showed a statistically significant increase in power within regions of the gamma band during the response phase compared with the fixation phase. In these 5 patients, the 95% bootstrapped confidence intervals of trial-averaged power in contiguous frequencies of the gamma band during the response phase were above, and did not overlap with, the confidence intervals of trial-averaged power during the fixation phase.

Conclusions: To the authors' knowledge, this is the first time that direct neural recordings have been used to show gamma-band modulation in the human amygdala during the execution of voluntary movement. This work indicates that gamma-band modulation in the amygdala could be a contributing source of neural signals for use in a motor BCI system.
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http://dx.doi.org/10.3171/2020.4.FOCUS20179DOI Listing
July 2020

Epidemiologic Assessment of Concussions in an NCAA Division I Women's Soccer Team.

Orthop J Sports Med 2020 May 15;8(5):2325967120921746. Epub 2020 May 15.

USC Epstein Family Center for Sports Medicine at Keck Medicine of USC, Los Angeles, California, USA.

Background: Among collegiate sports, ice hockey and wrestling have been reported to have the highest rates of concussion injury. Recent literature has shown that among all sports, female soccer players had the highest rate of concussion injury at the high school level. Sport-specific analysis will increase our knowledge of epidemiologic characteristics of this serious injury in young soccer players, where "heading" is commonly involved during participation.

Hypothesis: Heading during soccer will be associated with increased frequency of concussion injury in collegiate female players compared with other mechanisms of injury, and concussion injury mechanism and rates will differ by setting of injury (practice or match) and player position.

Study Design: Descriptive epidemiologic study.

Methods: This was a retrospective review and epidemiologic analysis of all concussions documented from a single National Collegiate Athletic Association (NCAA) Division I female collegiate soccer team between 2004 and 2017. A total of 381 participants were reviewed, and concussion injury mechanism, setting (practice or match), player position, and number of games and practices missed due to injury were analyzed.

Results: Overall, 25 concussions in 22 players from the 2004 to 2017 seasons were identified, for an annual rate of 1.79 concussions per year. Collisions (36%) followed by headers (20%) were the most common mechanisms. Forwards sustained the most concussions (32%). Injuries were more common in games (56%) than practice (40%). Of note, the most common cause of concussion during practice was headers (40%). Of the concussions documented, 20 (91%) were the player's first concussion. On average, each concussion resulted in a player missing 3.96 games and 12.46 practices.

Conclusion: Our results demonstrate that concussion rates in female NCAA soccer players vary by position and occur with different frequencies and mechanisms in practice and games. Interventions for concussion avoidance should aim to limit exposure to high-risk activity, including player-to-player contact in games and headers in practice. Although gameplay and collisions can be unpredictable and difficult to control, practice settings can be modified in an attempt to decrease risk.
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http://dx.doi.org/10.1177/2325967120921746DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7232119PMC
May 2020

Beta-band power modulation in the human hippocampus during a reaching task.

J Neural Eng 2020 06 12;17(3):036022. Epub 2020 Jun 12.

Department of Neurological Surgery, Keck School of Medicine of USC, University of Southern California, Los Angeles, CA, United States of America.

Objective: Characterize the role of the beta-band (13-30 Hz) in the human hippocampus during the execution of voluntary movement.

Approach: We recorded electrophysiological activity in human hippocampus during a reach task using stereotactic electroencephalography (SEEG). SEEG has previously been utilized to study the theta band (3-8 Hz) in conflict processing and spatial navigation, but most studies of hippocampal activity during movement have used noninvasive measures such as fMRI. We analyzed modulation in the beta band (13-30 Hz), which is known to play a prominent role throughout the motor system including the cerebral cortex and basal ganglia. We conducted the classic 'center-out' direct-reach experiment with nine patients undergoing surgical treatment for medically refractory epilepsy.

Main Results: In seven of the nine patients, power spectral analysis showed a statistically significant decrease in power within the beta band (13-30 Hz) during the response phase, compared to the fixation phase, of the center-out direct-reach task using the Wilcoxon signed-rank hypothesis test (p < 0.05).

Significance: This finding is consistent with previous literature suggesting that the hippocampus may be involved in the execution of movement, and it is the first time that changes in beta-band power have been demonstrated in the hippocampus using human electrophysiology. Our findings suggest that beta-band modulation in the human hippocampus may play a role in the execution of voluntary movement.
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http://dx.doi.org/10.1088/1741-2552/ab937fDOI Listing
June 2020

Optimal artifact suppression in simultaneous electrocorticography stimulation and recording for bi-directional brain-computer interface applications.

J Neural Eng 2020 04 29;17(2):026038. Epub 2020 Apr 29.

Department of Electrical Engineering and Computer Science, University of California, Irvine, Irvine, CA, 92697, United States of America.

Objective: Electrocorticogram (ECoG)-based brain-computer interfaces (BCIs) are a promising platform for the restoration of motor and sensory functions to those with neurological deficits. Such bi-directional BCI operation necessitates simultaneous ECoG recording and stimulation, which is challenging given the presence of strong stimulation artifacts. This problem is exacerbated if the BCI's analog front-end operates in an ultra-low power regime, which is a basic requirement for fully implantable medical devices. In this study, we developed a novel method for the suppression of stimulation artifacts before they reach the analog front-end.

Approach: Using elementary biophysical considerations, we devised an artifact suppression method that employs a weak auxiliary stimulation delivered between the primary stimulator and the recording grid. The exact location and amplitude of this auxiliary stimulating dipole were then found through a constrained optimization procedure. The performance of our method was tested in both simulations and phantom brain tissue experiments.

Main Results: The solution found through the optimization procedure matched the optimal canceling dipole in both simulations and experiments. Artifact suppression as large as 28.7 dB and 22.9 dB were achieved in simulations and brain phantom experiments, respectively.

Significance: We developed a simple constrained optimization-based method for finding the parameters of an auxiliary stimulating dipole that yields optimal artifact suppression. Our method suppresses stimulation artifacts before they reach the analog front-end and may prevent the front-end amplifiers from saturation. Additionally, it can be used along with other artifact mitigation techniques to further reduce stimulation artifacts.
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http://dx.doi.org/10.1088/1741-2552/ab82acDOI Listing
April 2020

Utility and lower limits of frequency detection in surface electrode stimulation for somatosensory brain-computer interface in humans.

Neurosurg Focus 2020 02;48(2):E2

Departments of1Neurosurgery and.

Objective: Stimulation of the primary somatosensory cortex (S1) has been successful in evoking artificial somatosensation in both humans and animals, but much is unknown about the optimal stimulation parameters needed to generate robust percepts of somatosensation. In this study, the authors investigated frequency as an adjustable stimulation parameter for artificial somatosensation in a closed-loop brain-computer interface (BCI) system.

Methods: Three epilepsy patients with subdural mini-electrocorticography grids over the hand area of S1 were asked to compare the percepts elicited with different stimulation frequencies. Amplitude, pulse width, and duration were held constant across all trials. In each trial, subjects experienced 2 stimuli and reported which they thought was given at a higher stimulation frequency. Two paradigms were used: first, 50 versus 100 Hz to establish the utility of comparing frequencies, and then 2, 5, 10, 20, 50, or 100 Hz were pseudorandomly compared.

Results: As the magnitude of the stimulation frequency was increased, subjects described percepts that were "more intense" or "faster." Cumulatively, the participants achieved 98.0% accuracy when comparing stimulation at 50 and 100 Hz. In the second paradigm, the corresponding overall accuracy was 73.3%. If both tested frequencies were less than or equal to 10 Hz, accuracy was 41.7% and increased to 79.4% when one frequency was greater than 10 Hz (p = 0.01). When both stimulation frequencies were 20 Hz or less, accuracy was 40.7% compared with 91.7% when one frequency was greater than 20 Hz (p < 0.001). Accuracy was 85% in trials in which 50 Hz was the higher stimulation frequency. Therefore, the lower limit of detection occurred at 20 Hz, and accuracy decreased significantly when lower frequencies were tested. In trials testing 10 Hz versus 20 Hz, accuracy was 16.7% compared with 85.7% in trials testing 20 Hz versus 50 Hz (p < 0.05). Accuracy was greater than chance at frequency differences greater than or equal to 30 Hz.

Conclusions: Frequencies greater than 20 Hz may be used as an adjustable parameter to elicit distinguishable percepts. These findings may be useful in informing the settings and the degrees of freedom achievable in future BCI systems.
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http://dx.doi.org/10.3171/2019.11.FOCUS19696DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7242113PMC
February 2020

Prospects of Photo- and Thermoacoustic Imaging in Neurosurgery.

Neurosurgery 2020 07;87(1):11-24

Neurorestoration Center, Keck School of Medicine, University of Southern California, Los Angeles, California.

The evolution of neurosurgery has been, and continues to be, closely associated with innovations in technology. Modern neurosurgery is wed to imaging technology and the future promises even more dependence on anatomic and, perhaps more importantly, functional imaging. The photoacoustic phenomenon was described nearly 140 yr ago; however, biomedical applications for this technology have only recently received significant attention. Light-based photoacoustic and microwave-based thermoacoustic technologies represent novel biomedical imaging modalities with broad application potential within and beyond neurosurgery. These technologies offer excellent imaging resolution while generally considered safer, more portable, versatile, and convenient than current imaging technologies. In this review, we summarize the current state of knowledge regarding photoacoustic and thermoacoustic imaging and their potential impact on the field of neurosurgery.
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http://dx.doi.org/10.1093/neuros/nyz420DOI Listing
July 2020

A benchtop system to assess the feasibility of a fully independent and implantable brain-machine interface.

J Neural Eng 2019 11 12;16(6):066043. Epub 2019 Nov 12.

Department of Biomedical Engineering, University of California, Irvine, CA 92697, United States of America.

Objective: State-of-the-art invasive brain-machine interfaces (BMIs) have shown significant promise, but rely on external electronics and wired connections between the brain and these external components. This configuration presents health risks and limits practical use. These limitations can be addressed by designing a fully implantable BMI similar to existing FDA-approved implantable devices. Here, a prototype BMI system whose size and power consumption are comparable to those of fully implantable medical devices was designed and implemented, and its performance was tested at the benchtop and bedside.

Approach: A prototype of a fully implantable BMI system was designed and implemented as a miniaturized embedded system. This benchtop analogue was tested in its ability to acquire signals, train a decoder, perform online decoding, wirelessly control external devices, and operate independently on battery. Furthermore, performance metrics such as power consumption were benchmarked.

Main Results: An analogue of a fully implantable BMI was fabricated with a miniaturized form factor. A patient undergoing epilepsy surgery evaluation with an electrocorticogram (ECoG) grid implanted over the primary motor cortex was recruited to operate the system. Seven online runs were performed with an average binary state decoding accuracy of 87.0% (lag optimized, or 85.0% at fixed latency). The system was powered by a wirelessly rechargeable battery, consumed  ∼150 mW, and operated for  >60 h on a single battery cycle.

Significance: The BMI analogue achieved immediate and accurate decoding of ECoG signals underlying hand movements. A wirelessly rechargeable battery and other supporting functions allowed the system to function independently. In addition to the small footprint and acceptable power and heat dissipation, these results suggest that fully implantable BMI systems are feasible.
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http://dx.doi.org/10.1088/1741-2552/ab4b0cDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7271898PMC
November 2019

Comparison of Intraoperative 3-Dimensional Fluoroscopy With Standard Computed Tomography for Stereotactic Frame Registration.

Oper Neurosurg (Hagerstown) 2020 06;18(6):698-709

Department of Neurological Surgery, Keck School of Medicine, University of Southern California, Los Angeles, California.

Background: Three-dimensional fluoroscopy via the O-arm (Medtronic, Dublin, Ireland) has been validated for intraoperative confirmation of successful lead placement in stereotactic electrode implantation. However, its role in registration and targeting has not yet been studied. After frame placement, many stereotactic neurosurgeons obtain a computed tomography (CT) scan and merge it with a preoperative magnetic resonance imaging (MRI) scan to generate planning coordinates; potential disadvantages of this practice include increased procedure time and limited scanner availability.

Objective: To evaluate whether the second-generation O-arm (O2) can be used in lieu of a traditional CT scan to obtain accurate frame-registration scans.

Methods: In 7 patients, a postframe placement CT scan was merged with preoperative MRI and used to generate lead implantation coordinates. After implantation, the fiducial box was again placed on the patient to obtain an O2 confirmation scan. Vector, scalar, and Euclidean differences between analogous X, Y, and Z coordinates from fused O2/MRI and CT/MRI scans were calculated for 33 electrode target coordinates across 7 patients.

Results: Marginal means of difference for vector (X = -0.079 ± 0.099 mm; Y = -0.076 ± 0.134 mm; Z = -0.267 ± 0.318 mm), scalar (X = -0.146 ± 0.160 mm; Y = -0.306 ± 0.106 mm; Z = 0.339 ± 0.407 mm), and Euclidean differences (0.886 ± 0.190 mm) remained within the predefined equivalence margin differences of -2 mm and 2 mm.

Conclusion: This study demonstrates that O2 may emerge as a viable alternative to the traditional CT scanner for generating planning coordinates. Adopting the O2 as a perioperative tool may offer reduced transport risks, decreased anesthesia time, and greater surgical efficiency.
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http://dx.doi.org/10.1093/ons/opz296DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7225008PMC
June 2020

Functional Frequency Discrimination From Cortical Somatosensory Stimulation in Humans.

Front Neurosci 2019 7;13:832. Epub 2019 Aug 7.

Department of Neurosurgery, University of Southern California, Los Angeles, CA, United States.

Recently, efforts to produce artificial sensation through cortical stimulation of primary somatosensory cortex (PSC) in humans have proven safe and reliable. Changes in stimulation parameters like frequency and amplitude have been shown to elicit different percepts, but without clearly defined psychometric profiles. This study investigates the functionally useful limits of frequency changes on the percepts felt by three epilepsy patients with subdural electrocorticography (ECoG) grids. Subjects performing a hidden target task were stimulated with parameters of constant amplitude, pulse-width, and pulse-duration, and a randomly selected set of two frequencies (20, 30, 40, 50, 60, and 100 Hz). They were asked to decide which target had the "higher" frequency. Objectively, an increase in frequency differences was associated with an increase in perceived intensity. Reliable detection of stimulation occurred at and above 40 Hz with a lower limit of detection around 20 Hz and a just-noticeable difference estimated at less than 10 Hz. These findings suggest that frequency can be used as a reliable, adjustable parameter and may be useful in establishing settings and thresholds of functionality in future BCI systems.
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http://dx.doi.org/10.3389/fnins.2019.00832DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6692717PMC
August 2019

Clinical neuroprosthetics: Today and tomorrow.

J Clin Neurosci 2019 Oct 30;68:13-19. Epub 2019 Jul 30.

Department of Neurological Surgery, Keck School of Medicine of USC, University of Southern California, Los Angeles, CA, USA; USC Neurorestoration Center, Keck School of Medicine of USC, Los Angeles, CA, USA; Department of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA, USA.

Implantable neurostimulation devices provide a direct therapeutic link to the nervous system and can be considered brain-computer interfaces (BCI). Under this definition, BCI are not simply science fiction, they are part of existing neurosurgical practice. Clinical BCI are standard of care for historically difficult to treat neurological disorders. These systems target the central and peripheral nervous system and include Vagus Nerve Stimulation, Responsive Neurostimulation, and Deep Brain Stimulation. Recent advances in clinical BCI have focused on creating "closed-loop" systems. These systems rely on biomarker feedback and promise individualized therapy with optimal stimulation delivery and minimal side effects. Success of clinical BCI has paralleled research efforts to create BCI that restore upper extremity motor and sensory function to patients. Efforts to develop closed loop motor/sensory BCI is linked to the successes of today's clinical BCI.
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http://dx.doi.org/10.1016/j.jocn.2019.07.056DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6717542PMC
October 2019

Directional tuning during reach planning in the supramarginal gyrus using local field potentials.

J Clin Neurosci 2019 Jun 22;64:214-219. Epub 2019 Apr 22.

Department of Neurological Surgery, Keck School of Medicine of USC, University of Southern California, Los Angeles, CA, United States; USC Neurorestoration Center, Keck School of Medicine of USC, Los Angeles, CA, United States.

Previous work in directional tuning for brain machine interfaces has primarily relied on algorithm sorted neuronal action potentials in primary motor cortex. However, local field potential has been utilized to show directional tuning in macaque studies, and inferior parietal cortex has shown increased neuronal activity in reaching tasks that relied on MRI imaging. In this study we utilized local field potential recordings from a human subject performing a delayed reach task and show that high frequency band (76-100 Hz) spectral power is directionally tuned to different reaching target locations during an active reach. We also show that during the delay phase of the task, directional tuning is present in areas of the inferior parietal cortex, in particular, the supramarginal gyrus.
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http://dx.doi.org/10.1016/j.jocn.2019.03.061DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7271900PMC
June 2019

Brain-Computer Interfaces in Quadriplegic Patients.

Neurosurg Clin N Am 2019 Apr 18;30(2):275-281. Epub 2019 Feb 18.

Department of Neurological Surgery, Keck School of Medicine of USC, University of Southern California, 1200 North State Street, Suite 3300, Los Angeles, CA 90033, USA; USC Neurorestoration Center, Keck School of Medicine of USC, University of Southern California, 1975 Zonal Ave, Los Angeles, CA 90033, USA; T&C Chen Brain Machine Interface Center, California Institute of Technology, 1200 E California Boulevard, Pasadena, CA 91125, USA; Department of Biology and Biological Engineering, California Institute of Technology, 1200 E California Boulevard, Pasadena, CA 91125, USA.

Brain-computer interfaces (BCI) are implantable devices that interface directly with the nervous system. BCI for quadriplegic patients restore function by reading motor intent from the brain and use the signal to control physical, virtual, and native prosthetic effectors. Future closed-loop motor BCI will incorporate sensory feedback to provide patients with an effective and intuitive experience. Development of widely available BCI for patients with neurologic injury will depend on the successes of today's clinical BCI. BCI are an exciting next step in the frontier of neuromodulation.
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http://dx.doi.org/10.1016/j.nec.2018.12.009DOI Listing
April 2019
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