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Tyree D Williams,1– 3 Talia Adler,2,4 Lindsey Smokoff,2,4 Anmoldeep Kaur,2,5 Benjamin Rodriguez,2,3,6 Kavita Jyoti Prakash,6 Edib Redzematovic,2 Turner S Baker,2,3,7 Benjamin I Rapoport,2,3 Edward S Yoon,8 Douglas P Beall,9 Jonathan S Dordick,1 Reade A De Leacy3 1Biomedical Engineering, Rensselaer Polytechnic Institute, Troy, NY, USA; 2Sinai BioDesign, Mount Sinai Medical System, New York, NY, USA; 3Department of Neurosurgery, Mount Sinai Medical System, New York, NY, USA; 4Columbia University School of General Studies, New York, NY, USA; 5Department of Neuroscience, Smith College, Northampton, MA, USA; 6Icahn School of Medicine at Mount Sinai, New York, NY, USA; 7Department of Population Health Science & Policy, Icahn School of Medicine at Mount Sinai, New York, NY, USA; 8Hospital for Special Surgery, New York, NY, USA; 9Spine Fracture Institute, Oklahoma City, OK, USACorrespondence: Benjamin Rodriguez, Department of Neurosurgery, Mount Sinai Medical System, One Gustave L. Levy Place, Box 1136, New York, NY, USA, Tel +1 615 524-0211, Email tyree.williams@mssm.eduAbstract: Vertebral compression fractures (VCFs) are common in osteoporotic patients, with a frequency projected to increase alongside a growing geriatric population. VCFs often result in debilitating back pain and decreased mobility. Cement augmentation, a minimally invasive surgical technique, is widely used to stabilize fractures and restore vertebral height. Acrylic-based cements and calcium phosphate cements are currently the two primary fill materials utilized for these procedures. Despite their effectiveness, acrylic bone cements and calcium phosphate cements have been associated with various intraoperative and postoperative incidents impacting VCF treatment. Over the past decade, discoveries in the field of biomedical engineering and material science have shown advancements toward addressing these limitations. This narrative review aims to assess the potential pitfalls and barriers of the various types of bone cements.Keywords: osteoporosis, vertebral compression fractures, bone cement, vertebroplasty, kyphoplasty, vertebral augmentation

Background: Endovascular embolization is an adjunct to meningioma resection. Isolating the effectiveness of embolization is difficult as MR imaging is typically performed before embolization and after resection, and volumetric assessment of embolization on 2D angiographic imaging is challenging. We investigated the correlation between 2D angiographic and 3D MR measurements of meningioma devascularization following embolization., Methods: We implemented a protocol for postembolization, preresection MRI. Angiographic devascularization was graded according to reduction of tumor blush from 1 (partial embolization) to 4 (complete embolization with no residual circulation supply). Volumetric extent of embolization was quantified as the percent of tumor contrast enhancement lost following embolization. Tumor embolization was analyzed according to tumor location and vascular supply., Results: Thirty consecutive patients met inclusionary criteria. Grade 1 devascularization was achieved in 7% of patients, grade 2 in 43%, grade 3 in 20%, and grade 4 in 30%. Average extent of embolization was 37 ± 6%. Extent of tumor embolization was low (<25%) in 40%, moderate (25%-75%) in 40%, and high (>75%) in 20% of patients. Convexity, parasagittal/falcine and sphenoid wing tumors were found to have distinct vascular supply patterns and extent of embolization. Angiographic devascularization grade was significantly correlated with volumetric extent of tumor embolization ( p  < 0.001, r  = 0.758)., Conclusion: This is the first study to implement postembolization, preoperative MRI to assess extent of embolization prior to meningioma resection. The study demonstrates that volumetric assessment of contrast reduction following embolization provides a quantitative and spatially resolved framework for assessing extent of tumor embolization., Competing Interests: Declaration of conflicting interestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Background and Objectives: Preoperative embolization is used as an endovascular adjunct to surgical resection of meningiomas. However, there is no standardized system to assess the efficacy or extent of embolization during the embolization procedure. We sought to establish a purely angiographic grading system to facilitate consistent reporting of the outcome of meningioma embolization and to characterize the anatomic and other features of meningiomas that predict the degree of devascularization achieved through preoperative embolization., Methods: We identified patients with meningiomas who underwent preoperative cerebral angiography and subsequent resection between 2015 and 2021. Demographic, clinical, and imaging data were collected in a research registry. We defined an angiographic devascularization grading scale as follows: grade 0 for no embolization, 1 for partial embolization, 2 for majority embolization, 3 for complete external carotid artery embolization, and 4 for complete embolization., Results: Eighty consecutive patients were included, 60 of whom underwent preoperative tumor embolization (20 underwent angiography with an intention to treat but ultimately not embolization). Embolized tumors were larger (59.0 vs 35.9 cc; P = .03). Gross total resection, length of stay, and complication rates did not differ among groups. The distribution of arterial feeders differed significantly across tumors in a location-specific manner. Both the tumor location and the identity of arterial feeders were predictive of the extent of embolization. Anterior midline meningiomas were associated with internal carotid (ophthalmic, ethmoidal) supply and lower devascularization grades (P = .03). Tumors fed by meningeal feeders (convexity, falcine, lateral sphenoid wing) were associated with higher devascularization grades (P < .01). The procedural complication rate for tumor embolization was 2.5%., Conclusion: Angiographic outcomes can be graded to indicate the extent of tumor embolization. This system may facilitate consistency of reported angiographic results. In addition, arterial feeders vary in a manner predicted by tumor location, and these patterns correlate with typical degrees of devascularization achieved in those tumor locations., (Copyright © 2024 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the Congress of Neurological Surgeons.)

The integration of robotics in surgery has increased over the past decade, and advances in the autonomous capabilities of surgical robots have paralleled that of assistive and industrial robots. However, classification and regulatory frameworks have not kept pace with the increasing autonomy of surgical robots. There is a need to modernize our classification to understand technological trends and prepare to regulate and streamline surgical practice around these robotic systems. We present a systematic review of all surgical robots cleared by the United States Food and Drug Administration (FDA) from 2015 to 2023, utilizing a classification system that we call Levels of Autonomy in Surgical Robotics (LASR) to categorize each robot's decision-making and action-taking abilities from Level 1 (Robot Assistance) to Level 5 (Full Autonomy). We searched the 510(k), De Novo, and AccessGUDID databases in December 2023 and included all medical devices fitting our definition of a surgical robot. 37,981 records were screened to identify 49 surgical robots. Most surgical robots were at Level 1 (86%) and some reached Level 3 (Conditional Autonomy) (6%). 2 surgical robots were recognized by the FDA to have machine learning-enabled capabilities, while more were reported to have these capabilities in their marketing materials. Most surgical robots were introduced via the 510(k) pathway, but a growing number via the De Novo pathway. This review highlights trends toward greater autonomy in surgical robotics. Implementing regulatory frameworks that acknowledge varying levels of autonomy in surgical robots may help ensure their safe and effective integration into surgical practice., (© 2024. The Author(s).)

Meningiomas with transosseous extension provide opportunities for extensive preoperative embolization, through conventional trans-arterial approaches, and also through less commonly used percutaneous methods. This video demonstrates embolization of a 7.6 × 9.5 × 9.9 cm transosseous WHO grade II meningioma. 1 Trans-arterial embolization was conducted via the left middle meningeal, occipital, and superficial temporal arteries. Only one superficial temporal artery was embolized to preserve vascular supply to the skin flap. To further devascularize the tumor, concomitant percutaneous embolization was performed. Transosseous extension of the tumor facilitated extensive percutaneous embolization of both the intracranial and extracranial components of the mass. Intraoperative bleeding from the scalp and extracranial component of the tumor was minimal. The intracranial tumor was soft and necrotic and was removed with suction and gentle dissection. Residual tumor was left behind within and adjacent to the superior sagittal sinus. The patient recovered without neurological deficit and was referred for radiation of the residual tumor., Competing Interests: Declaration of conflicting interestsThe author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Chronic subdural hematoma is one of the most common neurosurgical pathologies with over 160,000 cases in the United States and Europe each year. The current standard of care involves surgically evacuating the hematoma through a cranial opening, however, varied patient risk profiles, a significant recurrence rate, and increasing financial burden have sparked innovation in the field. This mini-review provides a brief overview of currently used evacuation techniques, including emerging adjuncts such as endoscopic assistance and middle meningeal artery embolization. This review synthesizes the body of available evidence on efficacy and risk profiles for each critical aspect of surgical technique in cSDH evacuation and provides insight into trends in the field and promising new technologies., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Rodriguez, Morgan, Young, Vlastos, Williams, Hrabarchuk, Tepper, Baker, Kellner, Bederson and Rapoport.)

Objective: Endonasal endoscopic odontoidectomy (EEO) is an alternative to transoral surgery for symptomatic ventral compression of the anterior cervicomedullary junction (CMJ), allowing for earlier extubation and feeding. Because the procedure destabilizes the C1-2 ligamentous complex, posterior cervical fusion is often performed concomitantly. The authors' institutional experience was reviewed to describe the indications, outcomes, and complications in a large series of EEO surgical procedures in which EEO was combined with posterior decompression and fusion., Methods: A consecutive, prospective series of patients who underwent EEO between 2011 and 2021 was studied. Demographic and outcome metrics, radiographic parameters, extent of ventral compression, extent of dens removal, and increase in CSF space ventral to the brainstem were measured on the preoperative and postoperative scans (first and most recent scans)., Results: Forty-two patients (26.2% pediatric) underwent EEO: 78.6% had basilar invagination, and 76.2% had Chiari type I malformation. The mean ± SD age was 33.6 ± 3.0 years, with a mean follow-up of 32.3 ± 4.0 months. The majority of patients (95.2%) underwent posterior decompression and fusion immediately before EEO. Two patients underwent prior fusion. There were 7 intraoperative CSF leaks but no postoperative CSF leaks. The inferior limit of decompression fell between the nasoaxial and rhinopalatine lines. The mean ± SD vertical height of dens resection was 11.98 ± 0.45 mm, equivalent to a mean ± SD resection of 74.18% ± 2.56%. The mean increase in ventral CSF space immediately postoperatively was 1.68 ± 0.17 mm (p < 0.0001), which increased to 2.75 ± 0.23 mm (p < 0.0001) at the most recent follow-up (p < 0.0001). The median (range) length of stay was 5 (2-33) days. The median time to extubation was 0 (0-3) days. The median time to oral feeding (defined as, at minimum, toleration of a clear liquid diet) was 1 (0-3) day. Symptoms improved in 97.6% of patients. Complications were rare and mostly associated with the cervical fusion portion of the combined surgical procedures., Conclusions: EEO is safe and effective for achieving anterior CMJ decompression and is often accompanied by posterior cervical stabilization. Ventral decompression improves over time. EEO should be considered for patients with appropriate indications.

Background: Middle meningeal artery (MMA) embolization has been recognized as a promising treatment for patients with subdural hematoma (SDH)., Objective: To present the technical feasibility and efficacy of n-butyl cyanoacrylate (n-BCA) embolization in the largest consecutive cohort to date., Methods: We retrospectively reviewed our consecutive cases of recurrent SDH treated with MMA embolization using diluted n-BCA with the "sugar rush" technique. In brief, a 2.1-Fr microcatheter was used to selectively catheterize the frontal and posterior branches of the MMA. 5% dextrose in water (D5W) was injected through an intermediate catheter while injecting n-BCA through the microcatheter. Complete obliteration of MMA and lack of SDH recurrence in a 3-6 months follow-up computed tomography scan were defined as efficacy outcomes. Cranial nerve palsy, vision loss, transient neurological deficit, and stroke were defined as safety outcomes., Results: A total of 61 patients were identified with a mean (±standard deviation) age of 62.5 ± 9 years. In 6 patients (10%), coil embolization of the origin of the frontal or posterior branch was performed because super-selective catheterization of the branch was unsuccessful because of tortuous anatomy. Complete obliteration of frontal and posterior branches was achieved in 100% of the cases. Recurrent SDH was seen in 3 patients (5%). No incidence of cranial nerve palsy, vision loss, or stroke occurred. One patient suffered a transient neurological deficit., Conclusion: MMA embolization using diluted n-BCA with concomitant D5W injection is associated with a high degree of distal penetration and complete branch occlusion and minimal risk of cranial nerve palsy or other thromboembolic complications., (Copyright © Congress of Neurological Surgeons 2022. All rights reserved.)

Background: Resection of large nerve sheath tumors in the lumbar spine using minimally invasive approaches is challenging, as approaches to tumors in this region may require facetectomy or partial resection of adjacent ribs for access to the involved neuroforamen and instrumentation across the involved joint to prevent subsequent kyphotic deformity., Objective: To describe a robot-assisted retroperitoneal approach for resection of a lumbar nerve sheath tumor, obviating the need for facetectomy and instrumentation. The operation is described, together with intraoperative images and an annotated video, in the context of a schwannoma arising from the right L1 root., Methods: The operation was performed by a urologic surgeon and a neurosurgeon. The patient was placed in lateral position, and the da Vinci Xi robot was used for retroperitoneal access via 5 ports along the right flank. Ultrasound was used to localize the tumor within the psoas. The tumor capsule was defined and released. Encountered nerves were stimulated, allowing small sensory nerves to be identified and safely divided. The tumor was traced into the right L1-L2 neuroforamen and removed., Results: Complete en bloc resection of the tumor was achieved, including the paraspinal and foraminal components, without any removal of bone and without violation of the dura., Conclusion: In selected patients, a robot-assisted retroperitoneal approach represents a minimally invasive alternative to traditional approaches for resection of lumbar nerve sheath tumors. This approach obviates the need for bone removal and instrumented spinal fusion. Interdisciplinary collaboration, as well as use of adjunctive technologies, including intraoperative ultrasound and neurophysiologic monitoring, is advised., (Copyright © 2020 by the Congress of Neurological Surgeons.)

Objective: Incomplete resection of skull base pathology may result in local tumor recurrence. This study investigates the utility of 5-aminolevulinic acid (5-ALA) fluorescence during endoscopic endonasal approaches (EEAs) to increase visibility of pathologic tissue., Methods: This retrospective multicenter series comprises patients with planned resection of an anterior skull base lesion who received preoperative 5-ALA at two tertiary care centers. Diagnostic use of a blue light endoscope was performed during EEA for all cases. Demographic and tumor characteristics as well as fluorescence status, quality, and homogeneity were assessed for each skull base pathology., Results: Twenty-eight skull base pathologies underwent blue-light EEA with preoperative 5-ALA, including 15 pituitary adenomas (54%), 4 meningiomas (14%), 3 craniopharyngiomas (11%), 2 Rathke's cleft cysts (7%), as well as plasmacytoma, esthesioneuroblastoma, and sinonasal squamous cell carcinoma. Of these, 6 (21%) of 28 showed invasive growth into surrounding structures such as dura, bone, or compartments of the cavernous sinus. Tumor fluorescence was detected in 2 cases (7%), with strong fluorescence in 1 tuberculum sellae meningioma and vague fluorescence in 1 pituicytoma. In all other cases fluorescence was absent. Faint fluorescence of the normal pituitary gland was seen in 1 (7%) of 15 cases. A comparison between the particular tumor entities as well as a correlation between invasiveness, WHO grade, Ki-67, and positive fluorescence did not show any significant association., Conclusions: With the possible exception of meningiomas, 5-ALA fluorescence has limited utility in the majority of endonasal skull base surgeries, although other pathology may be worth investigating.

Technical limitations and clinical challenges have historically limited the diagnostic tools and treatment methods available for surgical approaches to the management of epilepsy. By contrast, recent technological innovations in several areas hold significant promise in improving outcomes and decreasing morbidity. We review innovations in the neurosurgical management of epilepsy in several areas, including wireless recording and stimulation systems (particularly responsive neurostimulation [NeuroPace]), conformal electrodes for high-resolution electrocorticography, robot-assisted stereotactic surgery, optogenetics and optical imaging methods, novel positron emission tomography ligands, and new applications of focused ultrasonography. Investigation into genetic causes of and susceptibilities to epilepsy has introduced a new era of precision medicine, enabling the understanding of cell signaling mechanisms underlying epileptic activity as well as patient-specific molecularly targeted treatment options. We discuss the emerging path to individualized treatment plans, predicted outcomes, and improved selection of effective interventions, on the basis of these developments., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Background: Transforaminal endoscopic lumbar approaches involve working in Kambin's triangle. These procedures are performed on awake patients or under general anesthesia with continuous electromyography. Potential morbidity of this approach includes injury to exiting and traversing nerve roots, as substantial dissection or cauterization of overlying tissues is required for visualization., Methods: We developed a novel connection system that accepts input from a bipolar radiofrequency probe to allow direct nerve stimulation in conjunction with electromyography. This study included 30 consecutive patients undergoing transforaminal endoscopic lumbar approaches for discectomies (73.3%), foraminal stenosis (23.3%), or lateral recess stenosis (3.3%). Demographic, operative, and outcomes data were collected., Results: Average age of patients was 61.4 years, and the L4-5 segment was most commonly treated (65.6%). Electrophysiologic mapping of the exiting nerve root was attempted in 28 patients with an average stimulation threshold of 8.6 ± 0.9 mA. Mapping of the traversing nerve root was attempted in 12 patients with an average stimulation threshold of 6.0 ± 0.8 mA. There were no instances of new postoperative sensorimotor deficits or dysesthesia. These findings persisted through mean and median follow-up of 294 days and 165 days, respectively. No patient required subsequent lumbar surgery., Conclusions: Our modified instrumentation and technique allow for accurate identification of the exiting and traversing nerve roots with minimal changes to the workflow of transforaminal endoscopic lumbar approaches. Modification of a bipolar radiofrequency device connection arrangement is simple, inexpensive, and reusable. In this study, no patients developed injury or pain related to nerve root dysfunction., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Background and purpose Embolization of the middle meningeal artery (MMA) has recently been proposed as an alternative to surgery for treatment of chronic subdural hematoma (SDH), and several case reports have been published supporting its efficacy. It has been suggested that the primary pathologic process in chronic SDH is repeated microhemorrhaging into the subdural collection from fragile neovasculature within the SDH membrane that arises from distal branches of the MMA. Embolization could thus provide a means of eliminating this chronic rebleeding. Materials and methods Images were selected from MMA embolization procedures performed at our institution in order to illustrate the technique and theory behind its efficacy for treatment of chronic SDH. Results Images from MMA angiograms demonstrate the variability of MMA anatomy and help illustrate the importance of avoiding potential ophthalmic collaterals and branches supplying cranial nerves. The findings of irregular wispiness of the distal MMA vasculature, contrast outlining of the SDH membrane on angiography, and homogenous increased density within the SDH on postembolization head computed tomography are described. Conclusion MMA embolization may provide a safe alternative for treatment of chronic SDH, but careful angiographic assessment of MMA anatomy should be performed to avoid potential complications. The findings illustrated here lend support to the theory that the pathologic process of chronic SDH is repeated leakage of blood products from an inflamed, abnormal arterial neovasculature within the SDH membrane that arises from the MMA, and thus selective embolization could provide an effective treatment.

Background: Traditional treatment for symptomatic subdural hematoma (SDH) has been surgical evacuation, but recurrence rates are high and patients often harbor complex medical comorbidities. Growth and recurrence is thought to be due to the highly friable nature of the vascularized membrane that forms after initial injury. There have been reported cases of middle meningeal artery (MMA) embolization for treatment of recurrent SDH after surgical evacuation with the goal of eliminating the arterial supply to this vascularized membrane., Objective: To present the first known case series of MMA embolization as upfront treatment for symptomatic chronic SDHs that have failed conservative management in lieu of surgical evacuation., Methods: Five patients with symptomatic chronic SDHs underwent MMA embolization using PVA microparticles at our institution. Size of SDH was recorded in maximum diameter and total volume., Results: Four patients underwent unilateral and 1 underwent bilateral MMA embolization successfully. All cases had significant reduction in total volume of SDH at longest follow-up scan: 81.4 to 13.8 cc (7 wk), 48.5 to 8.7 cc (3 wk), 31.7 and 88 to 0 and 17 cc (14 wk, bilateral), 79.3 to 24.2 cc (8 wk), and 53.5 to 0 cc (6 wk). All patients had symptomatic relief with no complications. Histologic analysis of the chronic SDH membrane in a separate patient that required surgery revealed rich neovascularization with many capillaries and few small arterioles., Conclusion: MMA embolization could present a minimally invasive and low-risk initial treatment alternative to surgery for symptomatic chronic SDH when clinically appropriate.

Background and Importance: Herniated intervertebral disc fragments rarely penetrate the thecal sac, and intracranial hypotension attributable to such penetrating fragments is even more unusual. We describe the first reported case of a cranial neuropathy due to intradural herniation of a disc fragment, in which intracranial hypotension from a resulting cerebrospinal fluid leak caused bilateral abducens palsies., Clinical Presentation: A 45-year-old man presented with a positional headache after having experienced a "popping" sensation in his back while lifting a heavy object. He also reported blurred vision and was noted to have lateral gaze palsies bilaterally. Magnetic resonance imaging (MRI) of the brain revealed bilateral subdural collections, abnormal pachymeningeal enhancement, and cerebellar tonsillar herniation, suggesting intracranial hypotension. T2-weighted MRI of the spine revealed extrusion of the T12-L1 disc and suggested the presence of a disc fragment in the intradural space, displacing the caudal nerve roots. A myelogram demonstrated a filling defect extending into the subarachnoid space adjacent to the disc herniation, consistent with a free disc fragment in the intradural space. A diagnosis of intracranial hypotension due to a cerebrospinal fluid leak resulting from an intradural herniated disc was made. The diagnosis was confirmed intraoperatively., Conclusion: Surgical removal of the herniated disc fragment and repair of the dural defect resulted in complete resolution of the cranial neuropathy. This rare etiology of a cranial neuropathy, arising from pathology in the thoracolumbar spine, illustrates the clinical teaching that the sixth cranial nerve is highly sensitive to deformation induced by intracranial hypotension.

Background: Neurocysticercosis, an infection of the central nervous system with the larval cysts of the pork tapeworm, Taenia solium, is the most common parasitic disease of the central nervous system. The disease is a major global cause of acquired epilepsy and may also manifest as intracranial hypertension due to mass effect from large cysts or to cerebrospinal fluid flow obstruction by intraventricular cysts or inflammation of the subarachnoid space. While the condition is endemic in several regions of the world and has been appreciated as a public health problem in such regions for several decades, its emergence in the USA in areas far from the Mexican border is a more recent phenomenon., Methods: We present a case of surgically corrected acute hydrocephalus in a recent Haitian emigrant child due to a third ventricular neurocysticercal cyst complex., Results: We describe the endoscope-assisted en bloc removal of the complex, together with hydraulic maneuvers facilitating the removal of the intact cyst., Conclusions: Simple hydraulic maneuvers can facilitate the endoscopic en bloc removal of third ventricular neurocysticercal cysts.

Neural oscillations are important features in a working central nervous system, facilitating efficient communication across large networks of neurons. They are implicated in a diverse range of processes such as synchronization and synaptic plasticity, and can be seen in a variety of cognitive processes. For example, hippocampal theta oscillations are thought to be a crucial component of memory encoding and retrieval. To better study the role of these oscillations in various cognitive processes, and to be able to build clinical applications around them, accurate and precise estimations of the instantaneous frequency and phase are required. Here, we present methodology based on autoregressive modeling to accomplish this in real time. This allows the targeting of stimulation to a specific phase of a detected oscillation. We first assess performance of the algorithm on two signals where the exact phase and frequency are known. Then, using intracranial EEG recorded from two patients performing a Sternberg memory task, we characterize our algorithm's phase-locking performance on physiologic theta oscillations: optimizing algorithm parameters on the first patient using a genetic algorithm, we carried out cross-validation procedures on subsequent trials and electrodes within the same patient, as well as on data recorded from the second patient.

We have developed an implantable fuel cell that generates power through glucose oxidation, producing 3.4 μW cm(-2) steady-state power and up to 180 μW cm(-2) peak power. The fuel cell is manufactured using a novel approach, employing semiconductor fabrication techniques, and is therefore well suited for manufacture together with integrated circuits on a single silicon wafer. Thus, it can help enable implantable microelectronic systems with long-lifetime power sources that harvest energy from their surrounds. The fuel reactions are mediated by robust, solid state catalysts. Glucose is oxidized at the nanostructured surface of an activated platinum anode. Oxygen is reduced to water at the surface of a self-assembled network of single-walled carbon nanotubes, embedded in a Nafion film that forms the cathode and is exposed to the biological environment. The catalytic electrodes are separated by a Nafion membrane. The availability of fuel cell reactants, oxygen and glucose, only as a mixture in the physiologic environment, has traditionally posed a design challenge: Net current production requires oxidation and reduction to occur separately and selectively at the anode and cathode, respectively, to prevent electrochemical short circuits. Our fuel cell is configured in a half-open geometry that shields the anode while exposing the cathode, resulting in an oxygen gradient that strongly favors oxygen reduction at the cathode. Glucose reaches the shielded anode by diffusing through the nanotube mesh, which does not catalyze glucose oxidation, and the Nafion layers, which are permeable to small neutral and cationic species. We demonstrate computationally that the natural recirculation of cerebrospinal fluid around the human brain theoretically permits glucose energy harvesting at a rate on the order of at least 1 mW with no adverse physiologic effects. Low-power brain-machine interfaces can thus potentially benefit from having their implanted units powered or recharged by glucose fuel cells.

The ability to decode neural activity into meaningful control signals for prosthetic devices is critical to the development of clinically useful brain- machine interfaces (BMIs). Such systems require input from tens to hundreds of brain-implanted recording electrodes in order to deliver robust and accurate performance; in serving that primary function they should also minimize power dissipation in order to avoid damaging neural tissue; and they should transmit data wirelessly in order to minimize the risk of infection associated with chronic, transcutaneous implants. Electronic architectures for brain- machine interfaces must therefore minimize size and power consumption, while maximizing the ability to compress data to be transmitted over limited-bandwidth wireless channels. Here we present a system of extremely low computational complexity, designed for real-time decoding of neural signals, and suited for highly scalable implantable systems. Our programmable architecture is an explicit implementation of a universal computing machine emulating the dynamics of a network of integrate-and-fire neurons; it requires no arithmetic operations except for counting, and decodes neural signals using only computationally inexpensive logic operations. The simplicity of this architecture does not compromise its ability to compress raw neural data by factors greater than [Formula: see text]. We describe a set of decoding algorithms based on this computational architecture, one designed to operate within an implanted system, minimizing its power consumption and data transmission bandwidth; and a complementary set of algorithms for learning, programming the decoder, and postprocessing the decoded output, designed to operate in an external, nonimplanted unit. The implementation of the implantable portion is estimated to require fewer than 5000 operations per second. A proof-of-concept, 32-channel field-programmable gate array (FPGA) implementation of this portion is consequently energy efficient. We validate the performance of our overall system by decoding electrophysiologic data from a behaving rodent.

Neural oscillations are important features in a working central nervous system, facilitating efficient communication across large networks of neurons. To better study the role of these oscillations in various cognitive processes, and to be able to build clinical applications around them, accurate and precise estimations of the instantaneous frequency and phase are required. Here, we present methodology based on autoregressive modeling to accomplish this in real time. This allows the targeting of stimulation to a specific phase of a detected oscillation. Using intracranial EEG recorded from two patients performing a Sternberg memory task, we characterize our algorithm's phase-locking performance on physiologic theta oscillations.

Each year in the past three decades has seen hundreds of thousands of runners register to run a major marathon. Of those who attempt to race over the marathon distance of 26 miles and 385 yards (42.195 kilometers), more than two-fifths experience severe and performance-limiting depletion of physiologic carbohydrate reserves (a phenomenon known as 'hitting the wall'), and thousands drop out before reaching the finish lines (approximately 1-2% of those who start). Analyses of endurance physiology have often either used coarse approximations to suggest that human glycogen reserves are insufficient to fuel a marathon (making 'hitting the wall' seem inevitable), or implied that maximal glycogen loading is required in order to complete a marathon without 'hitting the wall.' The present computational study demonstrates that the energetic constraints on endurance runners are more subtle, and depend on several physiologic variables including the muscle mass distribution, liver and muscle glycogen densities, and running speed (exercise intensity as a fraction of aerobic capacity) of individual runners, in personalized but nevertheless quantifiable and predictable ways. The analytic approach presented here is used to estimate the distance at which runners will exhaust their glycogen stores as a function of running intensity. In so doing it also provides a basis for guidelines ensuring the safety and optimizing the performance of endurance runners, both by setting personally appropriate paces and by prescribing midrace fueling requirements for avoiding 'the wall.' The present analysis also sheds physiologically principled light on important standards in marathon running that until now have remained empirically defined: The qualifying times for the Boston Marathon.

Object: In the search for optimal monitoring and predictive tools in neurocritical care, the relationship of the pulsatile component of intracranial pressure (ICP) and the pressure itself has long been of great interest. Higher pressure often correlates with a higher pulsatile response to the heartbeat, interpreted as a type of compliance curve. Various mathematical approaches have been used, but regardless of the formula used, it is implicitly assumed that a reproducible curve exists. The authors investigated the stability of the correlation between static and pulsatile ICPs in patients with subarachnoid hemorrhage (SAH) who were observed for several hours by using data sets large enough to allow such calculations to be made., Methods: The ICP recordings were obtained in 39 patients with SAH and were parsed into 6-second time windows (1,998,944 windows in 197 recordings). The ICP parameters were computed for each window as follows: static ICP was defined as the mean ICP, and pulsatile ICP was characterized by mean ICP wave amplitude, rise time, and rise time coefficient., Results: The mean ICP and ICP wave amplitudes were simultaneously high or low (the expected correlation) in only approximately 60% of observations. Furthermore, static and pulsatile ICP correlated well only over short intervals; the degree of correlation weakened over periods of hours and was inconsistent across patients and within individual patients over time. Decorrelation originated with abrupt shifting and gradual drifting of mean ICP and ICP wave amplitude over several hours., Conclusions: The relationship between the static and pulsatile components of ICPs changes over time. It evolves, even in individual patients, over a number of hours. This can be one reason the observation of high pulsatile ICP (indicative of reduced intracranial compliance) despite normal mean ICP that is seen in some patients with SAH. The meaning and potential clinical usefulness of such changes in the curves is uncertain, but it implies that clinical events result not only from moving further out on a compliance curve; in practice, the curve, and the biological system that underlies the curve, may itself change.

Algorithmically and energetically efficient computational architectures that operate in real time are essential for clinically useful neural prosthetic devices. Such devices decode raw neural data to obtain direct control signals for external devices. They can also perform data compression and vastly reduce the bandwidth and consequently power expended in wireless transmission of raw data from implantable brain-machine interfaces. We describe a biomimetic algorithm and micropower analog circuit architecture for decoding neural cell ensemble signals. The decoding algorithm implements a continuous-time artificial neural network, using a bank of adaptive linear filters with kernels that emulate synaptic dynamics. The filters transform neural signal inputs into control-parameter outputs, and can be tuned automatically in an on-line learning process. We provide experimental validation of our system using neural data from thalamic head-direction cells in an awake behaving rat.

This paper presents work on ultra-low-power circuits for brain-machine interfaces with applications for paralysis prosthetics, stroke, Parkinson's disease, epilepsy, prosthetics for the blind, and experimental neuroscience systems. The circuits include a micropower neural amplifier with adaptive power biasing for use in multi-electrode arrays; an analog linear decoding and learning architecture for data compression; low-power radio-frequency (RF) impedance-modulation circuits for data telemetry that minimize power consumption of implanted systems in the body; a wireless link for efficient power transfer; mixed-signal system integration for efficiency, robustness, and programmability; and circuits for wireless stimulation of neurons with power-conserving sleep modes and awake modes. Experimental results from chips that have stimulated and recorded from neurons in the zebra finch brain and results from RF power-link, RF data-link, electrode-recording and electrode-stimulating systems are presented. Simulations of analog learning circuits that have successfully decoded prerecorded neural signals from a monkey brain are also presented.