Multi-electrode stimulation evokes consistent spatial patterns of phosphenes and improves phosphene mapping in blind subjects

BACKGROUND

Visual cortical prostheses (VCPs) have the potential to restore visual function to patients with acquired blindness. Successful implementation of VCPs requires the ability to reliably map the location of the phosphene produced by stimulation of each implanted electrode.

OBJECTIVE

To evaluate the efficacy of different approaches to phosphene mapping and propose simple improvements to mapping strategy.

METHODS

We stimulated electrodes implanted in the visual cortex of five blind and fifteen sighted patients. We tested two fixation strategies, unimanual fixation, where subjects placed a single index finger on a tactile fixation point and bimanual fixation, where subjects overlaid their right index finger over their left on the tactile point. In addition, we compared absolute mapping in which a single electrode was stimulated on each trial, and relative mapping with sequences containing stimulation of three to five phosphenes on each trial. Trial-to-trial variability present in relative mapping sequences was quantified.

RESULTS

Phosphene mapping was less precise in blind subjects than in sighted subjects (2DRMS, 16 ± 2.9° vs. 1.9 ± 0.93°; t (18) = 18, p = <0.001). Within blind subjects, bimanual fixation resulted in more consistent phosphene localization than unimanual fixation (BS1: 4.0 ± 2.6° vs. 19 ± 4.7°, t (79) = 24, p < 0.001; BS2 4.1 ± 2.0° vs. 12 ± 2.7°, t (65) = 19, p < 0.001). Multi-point relative mapping had similar baseline precision to absolute mapping (BS1: 4.7 ± 2.6° vs. 3.9 ± 2.0°; BS2: 4.1 ± 2.0° vs. 3.2 ± 1.1°) but improved significantly when trial-to-trial translational variability was removed. Although multi-point mapping methods did reveal more of the functional organization expected in early visual cortex, subjects tended to artificially regularize the spacing between phosphenes. We attempt to address this issue by fitting a standard logarithmic map to relative multi-point sequences.

CONCLUSIONS

Relative mapping methods, combined with bimanual fixation, resulted in the most precise estimates of phosphene organization. These techniques, combined with use of a standard logarithmic model of visual cortex, may provide a practical way to improve the implementation of a VCP.

Electrocorticography During Deep Brain Stimulation Surgery: Safety Experience From 4 Centers Within the National Institute of Neurological Disorders and Stroke Research Opportunities in Human Consortium

BACKGROUND

Intraoperative research during deep brain stimulation (DBS) surgery has enabled major advances in understanding movement disorders pathophysiology and potential mechanisms for therapeutic benefit. In particular, over the last decade, recording electrocorticography (ECoG) from the cortical surface, simultaneously with subcortical recordings, has become an important research tool for assessing basal ganglia-thalamocortical circuit physiology.

OBJECTIVE

To provide confirmation of the safety of performing ECoG during DBS surgery, using data from centers involved in 2 BRAIN (Brain Research through Advancing Innovative Neurotechnologies) Initiative-funded basic human neuroscience projects.

METHODS

Data were collected separately at 4 centers. The primary endpoint was complication rate, defined as any intraoperative event, infection, or postoperative magnetic resonance imaging abnormality requiring clinical follow-up. Complication rates for explanatory variables were compared using point biserial correlations and Fisher exact tests.

RESULTS

A total of 367 DBS surgeries involving ECoG were reviewed. No cortical hemorrhages were observed. Seven complications occurred: 4 intraparenchymal hemorrhages and 3 infections (complication rate of 1.91%; CI = 0.77%-3.89%). The placement of 2 separate ECoG research electrodes through a single burr hole (84 cases) did not result in a significantly different rate of complications, compared to placement of a single electrode (3.6% vs 1.5%; P = .4). Research data were obtained successfully in 350 surgeries (95.4%).

CONCLUSION

Combined with the single report previously available, which described no ECoG-related complications in a single-center cohort of 200 cases, these findings suggest that research ECOG during DBS surgery did not significantly alter complication rates.

Case Series: Deep Brain Stimulation for Facial Pain

BACKGROUND

Deep brain stimulation (DBS) has been used for chronic pain for decades, but its use is limited due to a lack of reliable data about its efficacy for specific indications.

OBJECTIVE

To report on 9 patients who underwent DBS for facial pain, with a focus on differences in outcomes between distinct etiologies.

METHODS

We retrospectively reviewed 9 patients with facial pain who were treated with DBS of the ventral posteromedial nucleus of the thalamus and periventricular gray. We report on characteristics including facial pain etiology, complications, changes in pain scores using the visual analog scale (VAS), and willingness to undergo DBS again.

RESULTS

Nine patients underwent DBS for either poststroke, post-traumatic, postherpetic, or atypical facial pain. Eight patients (89%) were permanently implanted. Seven patients had sufficient follow-up (mean 40.3 mo). Of these 7 patients, average VAS scores decreased from 9.4 to 6.1 after DBS. The average decrease in VAS was 55% for post-traumatic facial pain (2 patients), 45% for poststroke (2 patients), 15% for postherpetic neuralgia (2 patients), and 0% for atypical facial pain (1 patient). Three of the 8 implanted patients (38%) had complications which required removal of hardware. Only 2 of 7 (29%) patients met classical criteria for responders (50% decrease in pain scores). However, among 4 patients who were asked about willingness to undergo DBS again, all expressed that they would repeat the procedure.

CONCLUSION

There is a trend towards improvement in pain scores following DBS for facial pain, most prominently with post-traumatic pain.

Congress of Neurological Surgeons Systematic Review and Evidence-Based Guidelines for Deep Brain Stimulations for Obsessive-Compulsive Disorder: Update of the 2014 Guidelines

BACKGROUND

In 2020, the Guidelines Task Force conducted another systematic review of the relevant literature on deep brain stimulation (DBS) for obsessive-compulsive disorder (OCD) to update the original 2014 guidelines to ensure timeliness and accuracy for clinical practice.

OBJECTIVE

To conduct a systematic review of the literature and update the evidence-based guidelines on DBS for OCD.

METHODS

The Guidelines Task Force conducted another systematic review of the relevant literature, using the same search terms and strategies as used to search PubMed and Embase for relevant literature. The updated search included studies published between 1966 and December 2019. The same inclusion/exclusion criteria as the original guideline were also applied. Abstracts were reviewed and relevant full-text articles were retrieved and graded. Of 864 articles, 10 were retrieved for full-text review and analysis. Recommendations were updated according to new evidence yielded by this update.

RESULTS

Seven studies were included in the original guideline, reporting the use of bilateral DBS as more effective in improving OCD symptoms than sham treatment. An additional 10 studies were included in this update: 1 class II and 9 class III.

CONCLUSION

Based on the data published in the literature, the following recommendations can be made: (1) It is recommended that clinicians utilize bilateral subthalamic nucleus DBS over best medical management for the treatment of patients with medically refractory OCD (level I). (2) Clinicians may use bilateral nucleus accumbens or bed nucleus of stria terminalis DBS for the treatment of patients with medically refractory OCD (level II). There is insufficient evidence to make a recommendation for the identification of the most effective target.The full guidelines can be accessed at https://www.cns.org/guidelines/browse-guidelines-detail/deep-brain-stimulation-obsessive-compulsive-disord.

Generalizing neural signal-to-text brain-computer interfaces

Objective:Brain-Computer Interfaces (BCI) may help patients with faltering communication abilities due to neurodegenerative diseases produce text or speech by direct neural processing. However, their practical realization has proven difficult due to limitations in speed, accuracy, and generalizability of existing interfaces. The goal of this study is to evaluate the BCI performance of a robust speech decoding system that translates neural signals evoked by speech to a textual output. While previous studies have approached this problem by using neural signals to choose from a limited set of possible words, we employ a more general model that can type any word from a large corpus of English text.Approach:In this study, we create an end-to-end BCI that translates neural signals associated with overt speech into text output. Our decoding system first isolates frequency bands in the input depth-electrode signal encapsulating differential information regarding production of various phonemic classes. These bands form a feature set that then feeds into a Long Short-Term Memory (LSTM) model which discerns at each time point probability distributions across all phonemes uttered by a subject. Finally, a particle filtering algorithm temporally smooths these probabilities by incorporating prior knowledge of the English language to output text corresponding to the decoded word. The generalizability of our decoder is driven by the lack of a vocabulary constraint on this output word.Main result:This method was evaluated using a dataset of 6 neurosurgical patients implanted with intra-cranial depth electrodes to identify seizure foci for potential surgical treatment of epilepsy. We averaged 32% word accuracy and on the phoneme-level obtained 46% precision, 51% recall and 73.32% average phoneme error rate while also achieving significant increases in speed when compared to several other BCI approaches.Significance:Our study employs a more general neural signal-to-text model which could facilitate communication by patients in everyday environments.

A Novel Framework for Network-Targeted Neuropsychiatric Deep Brain Stimulation

Deep brain stimulation (DBS) has emerged as a promising therapy for neuropsychiatric illnesses, including depression and obsessive-compulsive disorder, but has shown inconsistent results in prior clinical trials. We propose a shift away from the empirical paradigm for developing new DBS applications, traditionally based on testing brain targets with conventional stimulation paradigms. Instead, we propose a multimodal approach centered on an individualized intracranial investigation adapted from the epilepsy monitoring experience, which integrates comprehensive behavioral assessment, such as the Research Domain Criteria proposed by the National Institutes of Mental Health. In this paradigm-shifting approach, we combine readouts obtained from neurophysiology, behavioral assessments, and self-report during broad exploration of stimulation parameters and behavioral tasks to inform the selection of ideal DBS parameters. Such an approach not only provides a foundational understanding of dysfunctional circuits underlying symptom domains in neuropsychiatric conditions but also aims to identify generalizable principles that can ultimately enable individualization and optimization of therapy without intracranial monitoring.

Movement-related changes in pallidocortical synchrony differentiate action execution and observation in humans

OBJECTIVE

Suppression of local and network alpha and beta oscillations in the human basal ganglia-thalamocortical (BGTC) circuit is a prominent feature of movement, including suppression of local alpha/beta power, cross-region beta phase coupling, and cortical and subcortical phase-amplitude coupling (PAC). We hypothesized that network-level coupling is more directly related to movement execution than local power changes, given the role of pathological network hypersynchrony in movement disorders such as Parkinson disease (PD). Understanding the specificity of these movement-related signals is important for designing novel therapeutics.

METHODS

We recorded globus pallidus internus (GPi) and motor cortical local field potentials during movement execution, passive movement observation and rest in 12 patients with PD undergoing deep brain stimulator implantation.

RESULTS

Local alpha/beta power is suppressed in the globus pallidus and motor cortex during both action execution and action observation, although less so during action observation. In contrast, pallidocortical phase synchrony and GPi and motor cortical alpha/beta-gamma PAC are suppressed only during action execution.

CONCLUSIONS

The functional dissociation across tasks in pallidocortical network activity suggests a particularly important role of network coupling in motor execution.

SIGNIFICANCE

Network level recordings provide important specificity in differentiating motor behavior and may provide significant value for future closed loop therapies.

Intra-Fraction Motion Management for Radiosurgical Treatments of Trigeminal Neuralgia: Clinical Experience, Imaging Frequency, and Motion Analysis

Purpose

The aim of this study is to evaluate the patient positioning and intra-fraction motion management performance of an image-guidance protocol established for radiosurgical treatments of trigeminal neuralgia patients. Specifically, it also aims to analyze patient motion data for the evaluation of current motion tolerance levels and imaging frequency utilized for repositioning patients.

Methods

A linear accelerator equipped with ExacTrac is used for patient positioning with stereoscopic imaging and treatments. Treatments are delivered with 4-mm conical collimators using seven equally spaced arcs. Arcs are 20 degrees apart and span 100 arc degrees each. Following initial ExacTrac positioning, cone beam computed tomography (CBCT) is obtained for independent confirmation of patient position. Patients are then stereoscopically imaged prior to the delivery of each arc and repositioned when 0.5-mm translational tolerance in any direction is exceeded. After the patient has been repositioned, verification stereoscopic images are obtained. Data from 48 patients with 607 image pairs were analyzed for this study.

Results

Over the course of 48 patient treatments, the mean magnitude of mean 3D deviations was 0.64 mm ± 0.12 mm (range: 0.07-2.74 mm). With the current 0.50-mm tolerance level for repositioning, patients exceeded the tolerance 51.4% of the time considering only images following an arc segment. For those instances, patients were repositioned with a mean magnitude of 0.85 mm ± 0.15 mm (1 SD). For a 0.25-mm tolerance level, 86.1% of arc segments would have required repositioning following the delivery of an arc segment, with a mean magnitude of 0.68 mm ± 0.12 mm. Conversely, for 0.75-mm and 1.00-mm tolerance levels, the tolerance would have been exceeded only 21.5% and 6.6% of instances following the delivery of an arc segment, with a mean magnitude of 1.08 mm ± 0.21 mm and 1.34 mm ± 0.24 mm, respectively. Each repositioning adds approximately 2 minutes to treatment time, which accounts for parts of the variability in patient treatment times. Following the initial ExacTrac and CBCT, the mean treatment time from first arc to treatment end was 57 minutes (range: 33-63 minutes).

Discussions

The current 0.50-mm tolerance level results in a clinically manageable but significant number of patient repositions during trigeminal neuralgia treatments. Frequent patient repositioning can result from actual patient motion convolved with the accuracy and precision limitations of the image analysis. Increasing the repositioning tolerance could more selectively correct for actual patient motion and shorten the treatment time at the expense of more variations in patient position. A more lenient tolerance level of 0.75 mm would decrease the repositioning rate by approximately a factor of 2; however, the permissible magnitude of motion will increase, leading to possible dosimetric consequences. Once treatment begins, there was no trend as to when patients exceeded the tolerance.

Conclusions

Current imaging protocol for patient positioning and intra-fraction motion management fits the clinical workflow with clinically acceptable residual patient motion. The next important step would be to assess how the number of repositions and magnitude of residual movements affect treatment outcomes.

Deep Brain Stimulation of the Subgenual Cingulate Cortex for the Treatment of Chronic Low Back Pain

OBJECTIVES

Despite converging basic scientific and clinical evidence of the link between chronic pain and depression, existing therapies do not often take advantage of this overlap. Here, we provide a critical review of the literature that highlights the intersection in brain networks between chronic low back pain (CLBP) and depression and discuss findings from previous deep brain stimulation (DBS) studies for pain. Based on a multidimensional model of pain processing and the connectivity of the subgenual cingulate cortex (SCC) with areas that are implicated in both CLBP and depression, we propose a novel approach to the treatment of CLBP using DBS of the SCC.

MATERIALS AND METHODS

A narrative review with literature assessment.

RESULTS

CLBP is associated with a shift away from somatosensory representation toward brain regions that mediate emotional processes. There is a high degree of overlap between these regions and those involved in depression, including the anterior cingulate cortex, medial prefrontal cortex, nucleus accumbens, and amygdala. Whereas targets sites from previous DBS trials for pain were not anatomically positioned to engage these areas and their associated networks, the SCC is structurally connected to all of these regions and as well as others involved in mediating sensory, cognitive, and affective processing in CLBP.

CONCLUSIONS

CLBP and depression share a common underlying brain network interconnected by the SCC. Current data and novel technology provide an optimal opportunity to develop clinically effective trials of SCC DBS for CLBP.

Proceedings of the Eighth Annual Deep Brain Stimulation Think Tank: Advances in Optogenetics, Ethical Issues Affecting DBS Research, Neuromodulatory Approaches for Depression, Adaptive Neurostimulation, and Emerging DBS Technologies

We estimate that 208,000 deep brain stimulation (DBS) devices have been implanted to address neurological and neuropsychiatric disorders worldwide. DBS Think Tank presenters pooled data and determined that DBS expanded in its scope and has been applied to multiple brain disorders in an effort to modulate neural circuitry. The DBS Think Tank was founded in 2012 providing a space where clinicians, engineers, researchers from industry and academia discuss current and emerging DBS technologies and logistical and ethical issues facing the field. The emphasis is on cutting edge research and collaboration aimed to advance the DBS field. The Eighth Annual DBS Think Tank was held virtually on September 1 and 2, 2020 (Zoom Video Communications) due to restrictions related to the COVID-19 pandemic. The meeting focused on advances in: (1) optogenetics as a tool for comprehending neurobiology of diseases and on optogenetically-inspired DBS, (2) cutting edge of emerging DBS technologies, (3) ethical issues affecting DBS research and access to care, (4) neuromodulatory approaches for depression, (5) advancing novel hardware, software and imaging methodologies, (6) use of neurophysiological signals in adaptive neurostimulation, and (7) use of more advanced technologies to improve DBS clinical outcomes. There were 178 attendees who participated in a DBS Think Tank survey, which revealed the expansion of DBS into several indications such as obesity, post-traumatic stress disorder, addiction and Alzheimer’s disease. This proceedings summarizes the advances discussed at the Eighth Annual DBS Think Tank.

Postoperative Admission of Adult Craniotomy Patients to the Neuroscience Ward Reduces Length of Stay and Cost

BACKGROUND

The neurointensive care unit (NICU) has traditionally been the default recovery unit after elective craniotomies.

OBJECTIVE

To assess whether admitting adult patients without significant comorbidities to the neuroscience ward (NW) instead of NICU for recovery resulted in similar clinical outcome while reducing length of stay (LOS) and hospitalization cost.

METHODS

We retrospectively analyzed the clinical and cost data of adult patients undergoing supratentorial craniotomy at a university hospital within a 5-yr period who had a LOS less than 7 d. We compared those admitted to the NICU for 1 night of recovery versus those directly admitted to the NW.

RESULTS

The NICU and NW groups included 340 and 209 patients, respectively, and were comparable in terms of age, ethnicity, overall health, and expected LOS. NW admissions had shorter LOS (3.046 vs 3.586 d, P < .001), and independently predicted shorter LOS in multivariate analysis. While the NICU group had longer surgeries (6.8 vs 6.4 h), there was no statistically significant difference in the cost of surgery. The NW group was associated with reduced hospitalization cost by $3193 per admission on average (P < .001). Clinically, there were no statistically significant differences in the rate of return to Operating Room, Emergency Department readmission, or hospital readmission within 30 d.

CONCLUSION

Admitting adult craniotomy patients without significant comorbidities, who are expected to have short LOS, to NW was associated with reduced LOS and total cost of admission, without significant differences in postoperative clinical outcome.

Increased structural connectivity of thalamic stimulation sites to motor cortex relates to tremor suppression

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Clinically weighted tractography reveals key patterns of therapeutic brain stimulation.

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Thalamic stimulation for tremor preferentially connects to precentral gyrus and cerebellum.

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Thalamic DBS of areas most connected to motor cortex results in superior outcomes.

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Acute and chronic therapeutic outcomes demonstrate converging connectivity patterns.

Deep brain stimulation (DBS) of the ventral intermediate nucleus (VIM-DBS) is a highly successful treatment for medication-refractory essential tremor (ET). Clinical outcomes are dependent on accurate targeting. Here, we aim to develop a framework for connectivity-guided DBS targeting by evaluating probabilistic tractography and clinical response at both initial programming (IP) and clinical follow-up (CF).

Magnetic resonance imaging and clinical outcomes were evaluated in 23 ET patients who were treated by VIM-DBS at the University of California Los Angeles (20 at IP, 18 at CF, 14 at both). Lead-DBS was used to model the volume of tissue activated tissue (VTA) based on programming configurations at both IP and CF. Probabilistic tractography, calculated in FSL, was used to evaluate 1) clinically weighted whole brain connectivity of VTA; 2) connectivity between VTA and freesurfer-derived target regions of interest (ROI) including primary motor, premotor, and prefrontal cortices, and cerebellum; and 3) volume of intersection between VTA and probabilistic tractography-based segmentation of the thalamus. At IP, individual contacts were scored as high or low efficacy based on acute tremor improvement. At CF, clinical response was measured by percent of change of the Clinical Rating Scale for Tremor (CRST) compared to preoperative scores. Contributions from each target ROI to clinical response was measured using logistic regression for IP and linear regression for CF.

The clinically weighted map of whole brain connectivity of VTA shows preferential connectivity to precentral gyrus and brainstem/cerebellum. The volume of intersection between VTA and thalamic segmentation map based on probabilistic connectivity to primary motor cortex was a significant predictor of contact efficacy at IP (OR = 2.26 per 100 mm³ of overlap, p = .04) and percent change in CRST at CF (β = 14.67 per 100 mm³ of overlap, p = .003).

Targeting DBS to the area of thalamus most connected to primary motor cortex based on probabilistic tractography is associated with superior outcomes, providing a potential guide not only for lead targeting but also therapeutic programming.

Distinct roles of dorsal and ventral subthalamic neurons in action selection and cancellation

The subthalamic nucleus (STN) supports action selection by inhibiting all motor programs except the desired one. Recent evidence suggests that STN can also cancel an already selected action when goals change, a key aspect of cognitive control. However, there is little neurophysiological evidence for dissociation between selecting and cancelling actions in the human STN. We recorded single neurons in the STN of humans performing a stop-signal task. Movement-related neurons suppressed their activity during successful stopping, whereas stop-signal neurons activated at low-latencies near the stop-signal reaction time. In contrast, STN and motor-cortical beta-bursting occurred only later in the stopping process. Task-related neuronal properties varied by recording location from dorsolateral movement to ventromedial stop-signal tuning. Therefore, action selection and cancellation coexist in STN but are anatomically segregated. These results show that human ventromedial STN neurons carry fast stop-related signals suitable for implementing cognitive control.

NeuroDAC: an open-source arbitrary biosignal waveform generator

Objective.Researchers are developing biomedical devices with embedded closed-loop algorithms for providing advanced adaptive therapies. As these devices become more capable and algorithms become more complex, tasked with integrating and interpreting multi-channel, multi-modal electrophysiological signals, there is a need for flexible bench-top testing and prototyping. We present a methodology for leveraging off-the-shelf audio equipment to construct a biosignal waveform generator capable of streaming pre-recorded biosignals from a host computer. By re-playing known, well-characterized, but physiologically relevant real-world biosignals into a device under test, researchers can evaluate their systems without the need for expensivein vivoexperiments.Approach.An open-source design based on the proposed methodology is described and validated, the NeuroDAC. NeuroDAC allows for 8 independent channels of biosignal playback using a simple, custom designed attenuation and buffering circuit. Applications can communicate with the device over a USB interface using standard audio drivers. On-board analog amplitude adjustment is used to maximize the dynamic range for a given signal and can be independently tuned for each channel.Main results.Low noise component selection yields a no-signal noise floor of just 5.35 ± 0.063. NeuroDAC's frequency response is characterized with a high pass -3 dB rolloff at 0.57 Hz, and is capable of accurately reproducing a wide assortment of biosignals ranging from EMG, EEG, and ECG to extracellularly recorded neural activity. We also present an application example using the device to test embedded algorithms on a closed-loop neural modulation device, the Medtronic RC+S.Significance.By making the design of NeuroDAC open-source we aim to present an accessible tool for rapidly prototyping new biomedical devices and algorithms than can be easily modified based on individual testing needs.ClinicalTrials.gov Identifiers: NCT04281134, NCT03437928, NCT03582891.

Variability of white matter anatomy in the subcallosal cingulate area

The subcallosal cingulate (SCC) area is a putative hub in the brain network underlying depression. Deep brain stimulation (DBS) targeting a particular subregion of SCC, identified as the intersection of forceps minor (FM), uncinate fasciculus (UCF), cingulum and fronto-striatal fiber bundles, may be critical to a therapeutic response in patients with severe, treatment-resistant forms of major depressive disorder (MDD). The pattern and variability of the white matter anatomy and organization within SCC has not been extensively characterized across individuals. The goal of this study is to investigate the variability of white matter bundles within the SCC that structurally connect this region with critical nodes in the depression network. Structural and diffusion data from 100 healthy subjects from the Human Connectome Project database were analyzed. Anatomically defined SCC regions were used as seeds to perform probabilistic tractography and to estimate the connectivity from the SCC to subject-specific target areas believed to be involved in the pathology of MDD including ventral striatum (VS), UCF, anterior cingulate cortex (ACC), and medial prefrontal cortex (mPFC). Four distinct areas of connectivity were identified within SCC across subjects: (a) postero-lateral SCC connectivity to medial temporal regions via UCF, (b) postero-medial connectivity to VS, (c) superior-medial connectivity to ACC via cingulum bundle, and (d) antero-lateral connectivity to mPFC regions via forceps minor. Assuming white matter connectivity is critical to therapeutic response, the improved anatomic understanding of SCC as well as an appreciation of the intersubject variability are critical to developing optimized therapeutic targeting for SCC DBS.

Local failure after stereotactic radiosurgery (SRS) for intracranial metastasis: analysis from a cooperative, prospective national registry

INTRODUCTION

Stereotactic radiosurgery (SRS) has been increasingly employed to treat patients with intracranial metastasis, both as a salvage treatment after failed whole brain radiation therapy (WBRT) and as an initial treatment. "Several studies have shown that SRS may be as effective as WBRT with the added benefit of preserving neuro-cognition". However, some patients may have local failure following SRS for intracranial metastasis, defined as increase in total lesion volume by 25% after at least 3 months of follow up.

METHODS

The SRS registry, established by the Neuro point alliance (NPA) under the auspices of the American Association of Neurological Surgeons (AANS), was queried for patients with intracranial metastasis receiving SRS at the participating sites. Demographic, clinical symptoms, tumor, and treatment characteristics as well as follow up status were summarized for the cohort. A multivariable explanatory cox- regression was performed to evaluate the impact of each of the factors on time to local failure.at last follow-up.

RESULTS

A total of 441 patients with 1255 intracranial metastatic lesions undergoing SRS were identified. The most common primary cancer histology was non-small cell lung cancer (43.8%, n = 193). More than half of the cohort had more than 1 metastatic lesion (2-3 lesions: 29.5%, n = 130; more than 3 lesions: 25.2% (n = 111). The average duration of follow-up for the cohort was found to be 8.4 months (SD = 7.61). The mean clinical treatment volume (CTV), after adding together the volume of each lesion for each patient was 5.39 cc (SD = 7.6) at baseline. A total of 20.2% (n = 89) had local failure (increase in volume by  > 25%) with a mean time to progression of 7.719 months (SD = 6.09). The progression free survival (PFS) for the cohort at 3, 6 and 12 months were found to be 94.9%, 84.3%, and 69.4%, respectively. On multivariable cox regression analysis, factors associated with increased hazard of local failure included male gender (HR 1.65, 95% CI 1.03-2.66, p = 0.037), chemotherapy at or before SRS (HR = 2.39, 95% CI 1.41-4.05, p = 0.001), WBRT at or before SRS (HR = 2.21, 95% CI 1.16- 4.22, p = 0.017), while surgical resection (HR 0.45, 95% CI 0.21-0. 97, p = 0.04) and immunotherapy (0.34, 95% CI 0.16-0.50, p = 0.014) were associated with lower hazard of local failure.

CONCLUSION

Factors found to be predictive of local failure included higher RPA score and those receiving chemotherapy, while patients undergoing surgical resection and those with occipital lobe lesions were less likely to experience local failure. Our analyses not only corroborate those previously reported but also demonstrate the utility of a multi-institutional registry to advance real-world SRS research for patients with intracranial metastatic lesions.

Longitudinal changes in blood-based biomarkers in chronic moderate to severe traumatic brain injury: preliminary findings

Objectives: This longitudinal study aims at 1) providing preliminary evidence of changes in blood-based biomarkers across time in chronic TBI and 2) relating these changes to outcome measures and cerebral structure and activity.Methods: Eight patients with moderate-to-severe TBI (7 males, 35 ± 7.6 years old, 5 severe TBI, 17.52 ± 3.84 months post-injury) were evaluated at monthly intervals across 6 time-points using: a) Blood-based biomarkers (GFAP, NSE, S100A12, SDBP145, UCH-L1, T-tau, P-tau, P-tau/T-tau ratio); b) Magnetic Resonance Imaging to evaluate changes in brain structure; c) Resting-state electroencephalograms to evaluate changes in brain function; and d) Outcome measures to assess cognition, emotion, and functional recovery (MOCA, RBANS, BDI-II, and DRS).Results: Changes in P-tau levels were found across time [p = .007]. P-tau was positively related to functional [p < .001] and cognitive [p = .006] outcomes, and negatively related to the severity of depression, 6 months later [R = -0.901; p =.006]. P-tau and P-tau/T-tau ratio were also positively correlated to shape change in subcortical areas such as brainstem [T(7) = 4.71, p = .008] and putamen [T(7) = 3.25, p = .012].Conclusions: Our study provides preliminary findings that suggest a positive relationship between P-tau and the recovery of patients with chronic TBI.

Deep Brain Electrode Externalization and Risk of Infection: A Systematic Review and Meta-Analysis

BACKGROUND

When evaluating deep brain stimulation (DBS) for newer indications, patients may benefit from trial stimulation prior to permanent implantation or for investigatory purposes. Although several case series have evaluated infectious complications among DBS patients who underwent trials with external hardware, outcomes have been inconsistent.

OBJECTIVE

To determine whether a period of lead externalization is associated with an increased risk of infection.

METHODS

We conducted a Preferred Reporting Items for Systematic Reviews and Meta-Analyses compliant systematic review of all studies that included rates of infection for patients who were externalized prior to DBS implantation. A meta-analysis of proportions was performed to estimate the pooled proportion of infection across studies, and a meta-analysis of relative risks was conducted on those studies that included a control group of nonexternalized patients. Heterogeneity across studies was assessed via I2 index.

RESULTS

Our search retrieved 23 articles, comprising 1354 patients who underwent lead externalization. The pooled proportion of infection was 6.9% (95% CI: 4.7%-9.5%), with a moderate to high level of heterogeneity between studies (I2 = 62.2%; 95% CI: 40.7-75.9; P < .0001). A total of 3 studies, comprising 212 externalized patients, included a control group. Rate of infection in externalized patients was 5.2% as compared to 6.0% in nonexternalized patients. However, meta-analysis was inadequately powered to determine whether there was indeed no difference in infection rate between the groups.

CONCLUSION

The rate of infection in patients with electrode externalization is comparable to that reported in the literature for DBS implantation without a trial period. Future studies are needed before this information can be confidently used in the clinical setting.

Dynamic Stimulation of Visual Cortex Produces Form Vision in Sighted and Blind Humans

A visual cortical prosthesis (VCP) has long been proposed as a strategy for restoring useful vision to the blind, under the assumption that visual percepts of small spots of light produced with electrical stimulation of visual cortex (phosphenes) will combine into coherent percepts of visual forms, like pixels on a video screen. We tested an alternative strategy in which shapes were traced on the surface of visual cortex by stimulating electrodes in dynamic sequence. In both sighted and blind participants, dynamic stimulation enabled accurate recognition of letter shapes predicted by the brain's spatial map of the visual world. Forms were presented and recognized rapidly by blind participants, up to 86 forms per minute. These findings demonstrate that a brain prosthetic can produce coherent percepts of visual forms.

Neural encoding of actual and imagined touch within human posterior parietal cortex

In the human posterior parietal cortex (PPC), single units encode high-dimensional information with partially mixed representations that enable small populations of neurons to encode many variables relevant to movement planning, execution, cognition, and perception. Here, we test whether a PPC neuronal population previously demonstrated to encode visual and motor information is similarly engaged in the somatosensory domain. We recorded neurons within the PPC of a human clinical trial participant during actual touch presentation and during a tactile imagery task. Neurons encoded actual touch at short latency with bilateral receptive fields, organized by body part, and covered all tested regions. The tactile imagery task evoked body part-specific responses that shared a neural substrate with actual touch. Our results are the first neuron-level evidence of touch encoding in human PPC and its cognitive engagement during a tactile imagery task, which may reflect semantic processing, attention, sensory anticipation, or imagined touch.

RADT-12. DISEASE CHARACTERISTICS IN ACUTE SEIZURE FOLLOWING RADIOTHERAPY FOR BRAIN METASTASES

INTRODUCTION

Acute seizure following radiotherapy (RT) for brain metastases is an infrequent but significant adverse event that has not been well-described. Prophylactic antiepileptic drug (AED) or steroid therapy is not recommended for asymptomatic lesions. However, there is minimal data incorporating individualized factors into acute seizure risk-assessment with respect to RT.

METHODS

We retrospectively examined patients treated for brain metastases with any RT modality from 2013-2020 who experienced acute post-treatment seizure, which we defined as within 4 weeks post-RT.

RESULTS

Twenty patients experienced acute seizure at median 2 days post-treatment (range 0-27); 15 (75%) within 7 days and 7 (35%) on day 0 (radiosurgery date or during fractionated RT). Seizures occurred after radiosurgery (n=9, 45%), fractionated stereotactic RT (n=3, 15%), whole-brain RT (n=5, 25%), and post-operative RT (n=3, 15%). All RT encompassed at least one supratentorial lesion; 11 (55%) had &gt;1 lesion treated. Median lesion size was 23mm (range 7-51mm). Moderate-to-severe perilesional edema was present in 12 (60%) and hemorrhage in 8 (40%) cases. Seizures occurred despite AED therapy in 8 (40%) overall; 5/8 (63%) were hemorrhagic and 7/8 (88%) had moderate-to-severe edema. Nine (45%) patients receiving steroids developed seizures. Primary pathologies were: melanoma (5), non-small cell lung (5), renal cell carcinoma (4), breast (3), colon (1), Merkel cell (1), and thyroid (1). Patients with melanoma who developed acute seizure had mainly non-hemorrhagic (80%), small lesions (median 9mm), not receiving AED (0%) or steroid (20%) therapy.

CONCLUSIONS

In acute post-RT seizure, lesions were predominantly supratentorial, &gt;23mm, and had moderate-to-severe edema. Breakthrough seizures were common in edematous and/or hemorrhagic lesions. However, acute seizure also occurred with smaller, non-hemorrhagic melanoma lesions not receiving AED therapy. A larger series is needed to further evaluate these identified characteristics in acute seizure, and whether prophylactic therapy may be appropriate.

A shared neural substrate for action verbs and observed actions in human posterior parietal cortex

High-level sensory and motor cortical areas are activated when processing the meaning of language, but it is unknown whether, and how, words share a neural substrate with corresponding sensorimotor representations. We recorded from single neurons in human posterior parietal cortex (PPC) while participants viewed action verbs and corresponding action videos from multiple views. We find that PPC neurons exhibit a common neural substrate for action verbs and observed actions. Further, videos were encoded with mixtures of invariant and idiosyncratic responses across views. Action verbs elicited selective responses from a fraction of these invariant and idiosyncratic neurons, without preference, thus associating with a statistical sampling of the diverse sensory representations related to the corresponding action concept. Controls indicated that the results are not the product of visual imagery or arbitrary learned associations. Our results suggest that language may activate the consolidated visual experience of the reader.

Steering the Volume of Tissue Activated With a Directional Deep Brain Stimulation Lead in the Globus Pallidus Pars Interna: A Modeling Study With Heterogeneous Tissue Properties

Objective: To study the effect of directional deep brain stimulation (DBS) electrode configuration and vertical electrode spacing on the volume of tissue activated (VTA) in the globus pallidus, pars interna (GPi). Background: Directional DBS leads may allow clinicians to precisely direct current fields to different functional networks within traditionally targeted brain areas. Modeling the shape and size of the VTA for various monopolar or bipolar configurations can inform clinical programming strategies for GPi DBS. However, many computational models of VTA are limited by assuming tissue homogeneity. Methods: We generated a multimodal image-based detailed anatomical (MIDA) computational model with a directional DBS lead (1.5 mm or 0.5 mm vertical electrode spacing) placed with segmented contact 2 at the ventral posterolateral "sensorimotor" region of the GPi. The effect of tissue heterogeneity was examined by replacing the MIDA tissues with a homogeneous tissue of conductance 0.3 S/m. DBS pulses (amplitude: 1 mA, pulse width: 60 μs, frequency: 130 Hz) were used to produce VTAs. The following DBS contact configurations were tested: single-segment monopole (2B-/Case+), two-segment monopole (2A-/2B-/Case+ and 2B-/3B-/Case+), ring monopole (2A-/2B-/2C-/Case+), one-cathode three-anode bipole (2B-/3A+/3B+/3C+), three-cathode three-anode bipole (2A-/2B-/2C-/3A+/3B+/3C+). Additionally, certain vertical configurations were repeated with 2 mA current amplitude. Results: Using a heterogeneous tissue model affected both the size and shape of the VTA in GPi. Electrodes with both 0.5 mm and 1.5 mm vertical spacing (1 mA) modeling showed that the single segment monopolar VTA was entirely contained within the GPi when the active electrode is placed at the posterolateral "sensorimotor" GPi. Two segments in a same ring and ring settings, however, produced VTAs outside of the GPi border that spread into adjacent white matter pathways, e.g., optic tract and internal capsule. Both stacked monopolar settings and vertical bipolar settings allowed activation of structures dorsal to the GPi in addition to the GPi. Modeling of the stacked monopolar settings with the DBS lead with 0.5 mm vertical electrode spacing further restricted VTAs within the GPi, but the VTA volumes were smaller compared to the equivalent settings of 1.5 mm spacing.

Altered Pallidocortical Low-Beta Oscillations During Self-Initiated Movements in Parkinson Disease

Background

Parkinson disease (PD) patients have difficulty with self-initiated (SI) movements, presumably related to basal ganglia thalamocortical (BGTC) circuit dysfunction, while showing less impairment with externally cued (EC) movements.

Objectives

We investigate the role of BGTC in movement initiation and the neural underpinning of impaired SI compared to EC movements in PD using multifocal intracranial recordings and correlating signals with symptom severity.

Methods

We compared time-resolved neural activities within and between globus pallidus internus (GPi) and motor cortex during between SI and EC movements recorded invasively in 13 PD patients undergoing deep brain stimulation implantation. We compared cortical (but not subcortical) dynamics with those recorded in 10 essential tremor (ET) patients, who do not have impairments in movement initiation.

Results

SI movements in PD are associated with greater low-beta (13–20 Hz) power suppression during pre-movement period in GPi and motor cortex compared to EC movements in PD and compared to SI movements in ET (motor cortex only). SI movements in PD are uniquely associated with significant low-beta pallidocortical coherence suppression during movement execution that correlates with bradykinesia severity. In ET, motor cortex neural dynamics during EC movements do not significantly differ from that observed in PD and do not significantly differ between SI and EC movements.

Conclusion

These findings implicate low beta BGTC oscillations in impaired SI movements in PD. These results provide a physiological basis for the strategy of using EC movements in PD, circumventing diseased neural circuits associated with SI movements and instead engaging circuits that function similarly to those without PD.

11. ASSOCIATION OF TUMOR EXPOSURE TO CEREBROSPINAL FLUID SPACES TO LEPTOMENINGEAL DISEASE IN PATIENTS WITH BRAIN METASTASES

BACKGROUND

Development of leptomeningeal disease in patients with brain metastases is associated with extremely poor survival. Identification of the underlying pathogenesis of leptomeningeal disease is unknown.

METHODS

This retrospective case control study included consecutive adult patients with at least one cerebral metastasis from a known extracranial primary solid malignancy and at least 3 month follow up (n=366). Patients were treated with radiotherapy with or without surgical resection and primary outcome was development of leptomeningeal disease.

RESULTS

The overall rate of leptomeningeal disease was 15.0%. Rates of development of leptomeningeal disease correlated with the presence of a dural based lesion (65.7% vs. 9.7%; P&lt;0.0001), intraventricular lesion (29.4% vs. 14.3%; P=0.0897), and with dural based lesions with sulcal or cortical enhancement (100% vs. 12.9%; P&lt;0.0001). Rates of developing leptomeningeal disease were not independently associated with surgical resection (17.2% vs. 14.2%; P=0.4859), however did occur significantly more often with piecemeal, as opposed to en bloc, resection (31.3% vs. 8.1%; P=0.0138) or when the ventricle was entered (61.5% vs. 18.9%; P&lt;0.0001).

CONCLUSIONS

Metastases that are in contact with cerebrospinal fluid spaces are associated with a higher rate of subsequent leptomeningeal disease, with or without surgical resection. Future studies should investigate the use of neoadjuvant radiation, whole brain radiation therapy or adherence to strict surgical technique in high risk brain metastasis patients to mitigate this probability.

The Curing Coma Campaign: Framing Initial Scientific Challenges-Proceedings of the First Curing Coma Campaign Scientific Advisory Council Meeting

Coma and disordered consciousness are common manifestations of acute neurological conditions and are among the most pervasive and challenging aspects of treatment in neurocritical care. Gaps exist in patient assessment, outcome prognostication, and treatment directed specifically at improving consciousness and cognitive recovery. In 2019, the Neurocritical Care Society (NCS) launched the Curing Coma Campaign in order to address the "grand challenge" of improving the management of patients with coma and decreased consciousness. One of the first steps was to bring together a Scientific Advisory Council including coma scientists, neurointensivists, neurorehabilitationists, and implementation experts in order to address the current scientific landscape and begin to develop a framework on how to move forward. This manuscript describes the proceedings of the first Curing Coma Campaign Scientific Advisory Council meeting which occurred in conjunction with the NCS Annual Meeting in October 2019 in Vancouver. Specifically, three major pillars were identified which should be considered: endotyping of coma and disorders of consciousness, biomarkers, and proof-of-concept clinical trials. Each is summarized with regard to current approach, benefits to the patient, family, and clinicians, and next steps. Integration of these three pillars will be essential to the success of the Curing Coma Campaign as will expanding the "curing coma community" to ensure broad participation of clinicians, scientists, and patient advocates with the goal of identifying and implementing treatments to fundamentally improve the outcome of patients.

Survival Outcomes After Intracranial Hemorrhage in Liver Disease

BACKGROUND

Survival outcomes for patients with liver disease who suffer an intracranial hemorrhage (ICH) have not been thoroughly investigated.

OBJECTIVE

To understand survival outcomes for 3 groups: (1) patients with an admission diagnosis of liver disease (end-stage liver disease [ESLD] or non-ESLD) who developed an ICH in the hospital, (2) patients with ESLD who undergo either operative vs nonoperative management, and (3) patients with ESLD on the liver transplant waitlist who developed an ICH in the hospital.

METHODS

We retrospectively reviewed hospital charts from March 2006 through February 2017 of patients with liver disease and an ICH evaluated by the neurosurgery service at a single academic medical center. The primary outcome was survival.

RESULTS

We included a total of 53 patients in this study. The overall survival for patients with an admission diagnosis of liver disease who developed an ICH (n = 29, 55%) in the hospital was 22%. Of those patients with an admission diagnosis of liver disease, 27 patients also had ESLD. Kaplan-Meier analysis found no significant difference in survival for ESLD patients (n = 33, 62%) according to operative status. There were 11 ESLD patients on the liver transplant waitlist. The overall survival for patients with ESLD on the liver transplant waitlist who suffered an in-hospital ICH (n = 7, 13%) was 14%.

CONCLUSION

ICH in the setting of liver disease carries a grave prognosis. Also, a survival advantage for surgical hematoma evacuation in ESLD patients is not clear.

Amygdala Structural Connectivity Is Associated With Impulsive Choice and Difficulty Quitting Smoking

Introduction: The amygdala is known to play a role in mediating emotion and possibly addiction. We used probabilistic tractography (PT) to evaluate whether structural connectivity of the amygdala to the brain reward network is associated with impulsive choice and tobacco smoking.

Methods: Diffusion and structural MRI scans were obtained from 197 healthy subjects (45 with a history of tobacco smoking) randomly sampled from the Human Connectome database. PT was performed to assess amygdala connectivity with several brain regions. Seed masks were generated, and statistical maps of amygdala connectivity were derived. Connectivity results were correlated with a subject performance both on a delayed discounting task and whether they met specified criteria for difficulty quitting smoking.

Results: Amygdala connectivity was spatially segregated, with the strongest connectivity to the hippocampus, orbitofrontal cortex (OFC), and brainstem. Connectivity with the hippocampus was associated with preference for larger delayed rewards, whereas connectivity with the OFC, rostral anterior cingulate cortex (rACC), and insula were associated with preference for smaller immediate rewards. Greater nicotine dependence with difficulty quitting was associated with less hippocampal and greater brainstem connectivity. Scores on the Fagerstrom Test for Nicotine Dependence (FTND) correlated with rACC connectivity.

Discussion: These findings highlight the importance of the amygdala-hippocampal-ACC network in the valuation of future rewards and substance dependence. These results will help to identify potential targets for neuromodulatory therapies for addiction and related disorders.

Subcallosal Cingulate Structural Connectivity Differs in Responders and Nonresponders to Electroconvulsive Therapy

BACKGROUND

Subcallosal cingulate (SCC) activity is associated with treatment response in major depressive disorder (MDD). Using electroconvulsive therapy (ECT) as a treatment model in this exploratory study, we addressed whether pretreatment SCC structural connectivity with corticolimbic-striatal circuitry relates to therapeutic outcome and whether these connectivity patterns change with treatment.

METHODS

Diffusion magnetic resonance imaging scans were acquired in 43 patients with MDD (mean [SD] age = 41 [13] years; men/women: 18/25) before and within 1 week of completing an ECT index series and in 31 healthy control subjects scanned twice (mean [SD] age = 38 [11] years; men/women: 17/18). Probabilistic tractography from subject-specific anatomically defined SCC seed regions to the ventral striatum (VS), anterior cingulate cortex (ACC), and bilateral medial prefrontal cortex (mPFC) was used to estimate structural connectivity in the target network.

RESULTS

SCC-mPFC connectivity was lower in responders (>50% symptom improvement) than nonresponders both before (p < .014) (difference 37%-96% left and right hemispheres) and after (p = .023) (difference 100% right hemisphere) treatment. SCC-mPFC connectivity in responders was also decreased compared with control subjects both at baseline (p = .012) and after ECT (p = .006), whereas nonresponders had SCC-right mPFC connectivity similar to that of control subjects. Subjects with MDD also showed decreased SCC-ACC connectivity compared with control subjects (baseline: p < .003, after ECT: p = .001), although SCC-ACC connectivity did not distinguish responders from nonresponders. Bilateral SCC-VS connectivity decreased (11%) with ECT (p = .021) regardless of treatment response.

CONCLUSIONS

While SCC-ACC connectivity may be a hallmark of MDD compared with control subjects, lower pretreatment SCC-mPFC connectivity in ECT responders (compared with nonresponders and control subjects) suggests that connectivity in this pathway may serve as a potential biomarker of therapeutic outcome and be relevant for treatment selection.

Propofol-induced loss of consciousness is associated with a decrease in thalamocortical connectivity in humans

Although the molecular effects of many anaesthetics have been well characterized, a network-level explanation for how these changes lead to loss of consciousness remains unclear. Studies using electroencephalography have characterized changes in neural oscillations in the cortex at specific frequency bands during propofol-induced anaesthesia and modelling work suggests these changes result from changes in thalamocortical functional connectivity. However, it is unclear if the neurophysiological changes seen at the cortex are due to enhanced or disrupted thalamocortical communication. Direct recordings from these sites during anaesthesia that could be used to confirm such models are rare. We recorded local field potentials from the ventral intermediate nucleus of the thalamus and electrocorticography signals from the ipsilateral sensorimotor cortex in 10 patients undergoing deep brain stimulation surgery. Signals were acquired during induction of propofol anaesthesia while subjects were resting. After confirming direct structural connectivity between the thalamus and the cortical recording site, we investigated propofol-associated changes in thalamic and cortical local power as well as thalamocortical functional connectivity, as measured with coherence, debiased weighted phase lag index, and phase amplitude coupling. Propofol anaesthesia resulted in local power increases at α frequencies (8-12 Hz) across both thalamic and cortical areas. At sensorimotor cortices, there was a broadband power increase (12-100 Hz), while the power of this same broad frequency band was suppressed within the thalamus. Despite the increase in local α power both within the thalamus and cortex, thalamocortical coherence and debiased weighted phase lag index in the α/low β frequencies (8-16 Hz, which was present in the awake state) significantly decreased with propofol administration (P < 0.05, two group test of coherence). Likewise, propofol administration resulted in decreased phase amplitude coupling between the phase of α/low β in the thalamus and the amplitude of broadband gamma (50-200 Hz) in the cortex (P = 0.031, Wilcoxon signed-rank test). We also report phase amplitude coupling between the phase of slow wave oscillations (0.1-1 Hz) and amplitude of broadband frequencies (8-200 Hz) within the cortex and across thalamocortical connections, during anaesthesia, both following a peak-max pattern. While confirming α-power increases with propofol administration both in thalamus and cortex, we observed decreased thalamocortical connectivity, contradicting models that suggest increasing cortical low frequency power is necessarily related to increased thalamocortical coherence but in support of the theory that propofol-induced loss of consciousness is associated with disrupted thalamocortical communication.

Electrophysiology and Structural Connectivity of the Posterior Hypothalamic Region: Much to Learn From a Rare Indication of Deep Brain Stimulation

Cluster headache (CH) is among the most common and debilitating autonomic cephalalgias. We characterize clinical outcomes of deep brain stimulation (DBS) to the posterior hypothalamic region through a novel analysis of the electrophysiological topography and tractography-based structural connectivity. The left posterior hypothalamus was targeted ipsilateral to the refractory CH symptoms. Intraoperatively, field potentials were captured in 1 mm depth increments. Whole-brain probabilistic tractography was conducted to assess the structural connectivity of the estimated volume of activated tissue (VAT) associated with therapeutic response. Stimulation of the posterior hypothalamic region led to the resolution of CH symptoms, and this benefit has persisted for 1.5-years post-surgically. Active contacts were within the posterior hypothalamus and dorsoposterior border of the ventral anterior thalamus (VAp). Delta- (3 Hz) and alpha-band (8 Hz) powers increased and peaked with proximity to the posterior hypothalamus. In the posterior hypothalamus, the delta-band phase was coupled to beta-band amplitude, the latter of which has been shown to increase during CH attacks. Finally, we identified that the VAT encompassing these regions had a high proportion of streamlines of pain processing regions, including the insula, anterior cingulate gyrus, inferior parietal lobe, precentral gyrus, and the brainstem. Our unique case study of posterior hypothalamic region DBS supports durable efficacy and provides a platform using electrophysiological topography and structural connectivity, to improve mechanistic understanding of CH and this promising therapy.

Impulsivity Relates to Relative Preservation of Mesolimbic Connectivity in Patients with Parkinson Disease

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Probabilistic tractography can identify functional subsegments of substantia nigra

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Topographic organization of subsegments is preserved in Parkinson patients

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Relative limbic-substantia nigra connectivity strength is associated with impulsivity

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Relative volume of substantia nigra subsegments is not associated with impulsivity

Introduction

The relationship between Parkinson Disease (PD) pathology, dopamine replacement therapy (DRT), and impulse control disorder (ICD) development is still incompletely understood. Given the sensorimotor-lateral substantia nigra (SN) selective degeneration associated with PD, we posit that a relative sparing of the limbic-medial SN in the context of DRT drives impulsive, reward-seeking behavior in PD patients with recent history of severe impulsivity.

Methods

Impulsive and control participants were selected from a consecutive list of PD patients receiving pre-operative deep brain stimulation (DBS) planning scans including 3T structural MRI and 64 direction diffusion tensor imaging (DTI). Using previously identified substantia nigra (SN) subsegment network connectivity profiles to develop classification targets, split-hemisphere target-based SN segmentation with probabilistic tractography was performed. The relative subsegment volumes and strength of connectivity between the SN and the limbic, associative, and motor network targets were compared.

Results

Our results show that there is greater probability of connectivity between the SN and limbic network targets relative to motor and associative network targets in PD patients with recent history of severe impulsivity as compared to PD patients without impulsivity (P = 0.0075). We did not observe relative volumetric subsegment differences across groups.

Conclusion

Firstly, our results suggest that fine-grained, atlas-derived classification targets may be used in PD to parcellate and classify functionally distinct subsegments of the SN, with the apparent preservation of previously reported topographical limbic-medial SN, associative-ventral SN, and sensorimotor-lateral SN orientation. We suggest that relative, as opposed to absolute, degeneration amongst SN-associated dopaminergic networks relates to the impulsivity phenotype in PD.

American Society for Stereotactic and Functional Neurosurgery Position Statement on Magnetic Resonance-Guided Focused Ultrasound for the Management of Essential Tremor

Magnetic resonance-guided focused ultrasound thalamotomy is a novel tool in the neurosurgical armamentarium for management of essential tremor (ET). Given the recent introduction of this technology, the American Society of Stereotactic and Functional Neurosurgery (ASSFN), which acts as the joint section representing the field of stereotactic and functional neurosurgery on behalf of the Congress of Neurological Surgeons and the American Association of Neurological Surgeons, provides here the expert consensus opinion on evidence-based best practices for the use and implementation of this treatment modality. Indications for treatment are outlined, including confirmed diagnosis of ET, failure to respond to first-line therapies, disabling appendicular tremor, and unilateral treatment are detailed, based on current evidence. Contraindications to therapy are also detailed. Finally, the evidence and authority on which the ASSFN bases this consensus position statement is detailed.

Characterization of pallidocortical motor network in Parkinson's disease through complex network analysis

OBJECTIVE

Deep brain stimulation (DBS) has been demonstrated by numerous clinical trials to be an advanced therapy for selected patients with Parkinson's disease (PD), while its maximal therapeutic effect is capped by the inadequate understanding of the precise neuronal mechanisms underlying PD. Recordings from multichannel electrodes placed in subcortical and cortical regions of the basal ganglia-thalamocortical (BGTC) motor network during DBS surgical procedures can provide rich physiologic information from accessible network nodes. However, most investigations focus on presumed spatio-spectral points of interest, neither fully utilizing the richness of spatial, spectral and temporal aspects of the multivariate signals nor making discoveries in the context of all possible candidates. In addition, aggregated network-level information has been missed out.

APPROACH

We use complex network analysis to characterize functional network characteristics of the pallidocortical subcircuit of the BGTC motor network in PD at rest and with movement. The network matrix was constructed using distinct frequency bands at each anatomic recording site as virtual nodes and spectral connectivity (through phase-amplitude coupling and coherence) as network edges.

MAIN RESULTS

We confirm the critical roles of beta bands and provide additional evidence on their differential functional roles in the pallidocortical motor network. Moreover, significant changes (p   <  0.05) in network functional segregation and integration between rest and movement conditions are revealed for the first time. More importantly, movement-dependent modulation of these network metrics are significantly correlated with hemibody unified PD rating scales (UPDRS), providing network-level perspectives of the pallidocortical motor network pertaining to PD symptoms (p   <  0.05).

SIGNIFICANCE

Findings in the present study provide network-level understanding of neuronal mechanisms in the pallidocortical motor network underlying PD. It is also highly plausible that the demonstrated approach can be applied in other important subcircuits towards a comprehensive understanding of the BGTC motor network.

Big Data Defined: A Practical Review for Neurosurgeons

BACKGROUND

Modern science and healthcare generate vast amounts of data, and, coupled with the increasingly inexpensive and accessible computing, a tremendous opportunity exists to use these data to improve care. A better understanding of data science and its relationship to neurosurgical practice will be increasingly important as we transition into this modern "big data" era.

METHODS

A review of the literature was performed for key articles referencing big data for neurosurgical care or related topics.

RESULTS

In the present report, we first defined the nature and scope of data science from a technical perspective. We then discussed its relationship to the modern neurosurgical practice, highlighting key references, which might form a useful introductory reading list.

CONCLUSIONS

Numerous challenges exist going forward; however, organized neurosurgery has an important role in fostering and facilitating these efforts to merge data science with neurosurgical practice.