Globus pallidus externus drives increase in network-wide alpha power with propofol-induced loss-of-consciousness in humans.

States of consciousness are likely mediated by multiple parallel yet interacting cortico-subcortical recurrent networks. Although the mesocircuit model has implicated the pallidocortical circuit as one such network, this circuit has not been extensively evaluated to identify network-level electrophysiological changes related to loss of consciousness (LOC). We characterize changes in the mesocircuit in awake versus propofol-induced LOC in humans by directly simultaneously recording from sensorimotor cortices (S1/M1) and globus pallidus interna and externa (GPi/GPe) in 12 patients with Parkinson disease undergoing deep brain stimulator implantation. Propofol-induced LOC is associated with increases in local power up to 20 Hz in GPi, 35 Hz in GPe, and 100 Hz in S1/M1. LOC is likewise marked by increased pallidocortical alpha synchrony across all nodes, with increased alpha/low beta Granger causal (GC) flow from GPe to all other nodes. In contrast, LOC is associated with decreased network-wide beta coupling and beta GC from M1 to the rest of the network. Results implicate an important and possibly central role of GPe in mediating LOC-related increases in alpha power, supporting a significant role of the GPe in modulating cortico-subcortical circuits for consciousness. Simultaneous LOC-related suppression of beta synchrony highlights that distinct oscillatory frequencies act independently, conveying unique network activity.

Resiliency of a perpetual optimist: neurosurgeon Dr. Linda Liau.

It is not possible to capture all the depth that composes Dr. Linda Liau: chair of the Neurosurgery Department at the University of California, Los Angeles; second woman to chair a neurosurgery program in the United States; first woman to chair the American Board of Neurological Surgery; first woman president of the Western Neurosurgical Society; and one of only a handful of neurosurgeons elected to the National Academy of Medicine. Her childhood and family history alone could fascinate several chapters of her life's biography. Nonetheless, this brief biography hopes to capture the challenges, triumphs, cultural norms, and spirit that have shaped Dr. Liau's experience as a successful leader, scientist, and neurosurgeon. This is a rare story. It describes the rise of not only an immigrant within neurosurgery-not unlike other giants in the field, Drs. Robert Spetzler, Jacques Marcos, Ossama Al-Mefty, and a handful of other contemporaries-but also another type of minority in neurosurgery: a woman.

Neurosurgeons in 2020: the impact of gender on neurosurgical training, family planning, and workplace culture.

OBJECTIVE: In 2008, a Women in Neurosurgery Committee white paper called for increased women applicants and decreased women's attrition in neurosurgery. However, contributing factors (work-life balance, lack of female leadership, workplace gender inequality) have not been well characterized; therefore, specific actions cannot be implemented to improve these professional hurdles. This study provides an update on the experiences of neurosurgeons in 2020 with these historical challenges. METHODS: An anonymous online survey was sent to all Accreditation Council for Graduate Medical Education (ACGME)-accredited US neurosurgical programs, examining demographics and experiences with mentorship, family life, fertility, and workplace conduct. RESULTS: A total of 115 respondents (64 men, 51 women; age range 25-67 years) had trained at 49 different US residencies. Mentorship rates were very high among men and women in medical school and residency. However, women were significantly more likely than men to have a female mentor in residency. During residency, 33% of women versus 44% of men had children, and significantly fewer women interested in having a child were able to do so in residency, compared to men. Significantly more women than men had a child only during a nonclinical year (56.3% vs 19.0%, respectively). Thirty-nine percent of women and 25% of men reported difficulty conceiving. The major difficulty for men was stress, whereas women reported the physical challenges of pregnancy itself (workplace teratogens, morning sickness, etc.). Failed birth rates peaked during residency (0.33) versus those before (0.00) and after residency (0.25).Women (80%) experience microaggressions in the workplace significantly more than men (36%; p < 0.001). Ninety-five percent of macro-/microaggressions toward female neurosurgeons were about their gender, compared to 9% of those toward men (p < 0.001). The most common overall perpetrators were senior male residents and attendings, followed by male patients (against women) and female nurses or midlevel providers (against men). CONCLUSIONS: Accurate depictions of neurosurgery experiences and open discussions of the potential impacts of gender may allow for 1) decreased attrition due to more accurate expectations and 2) improved characterization of gender differences in neurosurgery so the profession can work to address gender inequality.

Supinator to Posterior Interosseous Nerve Transfer for Recovery of Hand Opening in the Tetraplegic Patient: A Case Series.

BACKGROUND AND OBJECTIVES: Cervical spinal cord injury results in devastating loss of function. Nerve transfers can restore functional use of the hand, the highest priority function in this population to gain independence. Transfer of radial nerve branches innervating the supinator to the posterior interosseous nerve (SUP-PIN) has become a primary intervention for the recovery of hand opening, but few outcome reports exist to date. We report single-surgeon outcomes for this procedure. METHODS: The SUP-PIN transfer was performed on adults with traumatic spinal cord injury resulting in hand paralysis. Outcome measures include Medical Research Council strength grade for extension of each digit, and angles representing critical apertures: the first web space opening of the thumb, and metacarpophalangeal angle of the remaining fingers. Factors affecting these measurements, including preserved tone and spasticity of related muscles, were also assessed. RESULTS: Twenty-three adult patients with a C5-7 motor level underwent SUP-PIN transfers on 36 limbs (median age 31 years, interquartile range [21.5, 41]). The median interval from injury to surgery was 10.5 (8.2, 6.5) months, with 9 (7.5, 11) months for the acute injuries and 50 (32, 66) months for the chronic (>18 months) injuries. Outcomes were observed at a mean follow-up of 22 (14, 32.5) months. 30 (83.3%) hands recovered at least antigravity extension of the thumb and 34 (94.4%) demonstrated successful antigravity strength for the finger extensors, providing adequate opening for a functional grasp. Chronic patients (>18 months after injury) showed similar outcomes to those who had earlier surgery. Supination remained strong (at least M4) in all but a single patient and no complications were observed. CONCLUSION: SUP-PIN is a reliable procedure for recovery of finger extension. Chronic patients remain good candidates, provided innervation of target muscles is preserved. Higher C5 injuries were more likely to have poor outcomes.

Blood pressure cuff-induced radial nerve palsy following minimally invasive lateral microdiscectomy: illustrative case.

BACKGROUND: The authors describe a rare case of transient postoperative wrist and finger drop following a prone position minimally invasive surgery (MIS) lateral microdiscectomy. OBSERVATIONS: Hand and wrist drop is an unusual complication following spine surgery, especially in prone positioning. The authors' multidisciplinary team assessed a patient with this complication following MIS lateral microdiscectomy. The broad differential diagnosis included radial nerve palsy, C7 radiculopathy, stroke, and spinal cord injury. Given the patient's supinator weakness, intact pronation and wrist flexion, and transient recovery within 4 weeks, the most likely diagnosis was radial nerve neuropraxia secondary to ischemic compression. After careful consideration of the operative environment and anatomical constraints, the patient's blood pressure cuff was found to be the most probable source of compression. LESSONS: Blood pressure cuff-induced peripheral nerve injury may be a source of postoperative radial nerve neuropraxia in patients undergoing spine surgery. Careful considerations must be given to the blood pressure cuff location, which should not be placed at the distal end of the humerus due to higher susceptibility of peripheral nerve compression. Spine surgeons should be aware of and appropriately localize postoperative deficits along the neuroaxis, including central versus proximal or distal peripheral injuries, in order to guide appropriate postoperative management.

Axillary to Radial Nerve Transfer for Recovery of Elbow Extension After Spinal Cord Injury.

BACKGROUND AND OBJECTIVES: Cervical spinal cord injuries (SCI) result in severe loss of function and independence. Nerve transfers have become a powerful method for restoring upper extremity function, the most critical missing function desired by this patient population. Recovery of active elbow extension allows for expansion of one's workspace to reach for objects and stabilizes control at the elbow joint. Without triceps function, a patient with a cervical SCI is rendered entirely helpless when in the supine position. Our objective was to provide a concise description of the transfer of branches of the axillary nerve (AN) to the long head of the triceps branch of the radial nerve (RN) for restoration of elbow extension after cervical SCI. METHODS: An anterior, axillary approach is used for the transfer of the nerve branches of the AN (which may include branches to the teres minor, posterior deltoid, or even middle deltoid) to the long head of the triceps branch of the RN. Preoperative assessment and intraoperative stimulation are demonstrated to direct optimal selection of axillary branch donors. RESULTS: The axillary approach provides full access to all branches of the AN in optimal proximity to triceps branches of the RN and allows for tension-free coaptation to achieve successful recovery of elbow extension. Final outcomes may not be achieved for 18 months. Of our last 20 patients with greater than 12-month follow-up, 13 have achieved antigravity strength in elbow extension, 4 are demonstrating ongoing progression, and 3 are definitive failures by 18 months. CONCLUSION: The axillary to RN transfer is an important intervention for recovery of elbow extension after cervical SCI, which significantly improves quality of life in this patient population. Further large population outcomes studies are necessary to further establish efficacy and increase awareness of these procedures.

Selective Tibial Neurotomy for Spastic Equinovarus Foot: Operative Technique.

BACKGROUND AND OBJECTIVES: Spastic equinovarus foot (SEF) is a common complication of stroke and other upper motor neuron injuries. It is characterized by a plantigrade and inverted foot, often with toe curling, causing significant disability from pain, gait, and balance difficulties. Management includes physical therapy, antispasticity drugs, orthoses, chemical neurolysis, or botulinum toxin, all of which may be insufficient, sedating, or transient. Selective tibial neurotomy (STN) provides a surgical option that is effective and long-lasting. Our goal is to provide a concise description of our technique for performing the STN for treatment of SEF. We discuss the standard posterior approach with surgical variations used by other groups and a medial approach, should the posterior approach be insufficient. METHODS: A posterior leg approach allows access to the tibial nerve and its branches to the bilateral gastrocnemius muscles, soleus, posterior tibialis, and extrinsic toe flexors. A medial approach is used if the toe flexors cannot be accessed sufficiently from the posterior approach. Nerve branch targets identified by preoperative functional assessment are carefully exposed and fully neurolysed distally to identify all terminal branches to each muscle of interest before neurotomy. RESULTS: The STN is a powerful tool for treating SEF, with an immediate and lasting effect. Approximately 80% of the target muscle should be denervated to ensure long-term efficacy while maintaining adequate function of the muscle through collateral innervation. CONCLUSION: The STN is a safe and effective outpatient procedure that can be performed by an experienced nerve surgeon to improve balance and ambulation and reduce pain for patients with SEF. Large clinical trials are necessary to further establish this underutilized procedure in the United States.

Cataloging formal medical student surgical funding opportunities: A retrospective characterization.

Representation of female surgical residents has slowly increased, but underrepresented in medicine (URiM) representation remains disappointingly low. National residency matching reports suggest that meaningful research experience improves surgical residency match success - therefore, formal funding opportunities and early mentorship for URiM medical students. In this study, we catalog medical student (MS) funding opportunities (funding type, eligibility by year, mission, compensation, length of commitment, number of awardees, and dollar investment amount per student) from 7 surgical departments (general surgery, thoracic surgery, vascular surgery, plastic surgery, otorhinolaryngology, orthopedic surgery, neurosurgery) within 196 US medical schools and 20 professional surgical educational organizations through manually searching web pages. We recorded 146 surgical funding opportunities from medical school surgical departments and 16 surgical funding opportunities from professional organizations. Overall, we find that medical institutions' surgical departments and professional surgical educational organizations may not be effectively utilizing recruitment strategies in MS funding opportunities.

A scoping review of current and emerging techniques for evaluation of peripheral nerve health, degeneration, and regeneration: part 1, neurophysiology.

Peripheral neuroregeneration research and therapeutic options are expanding exponentially. With this expansion comes an increasing need to reliably evaluate and quantify nerve health. Valid and responsive measures that can serve as biomarkers of the nerve status are essential for both clinical and research purposes for diagnosis, longitudinal follow-up, and monitoring the impact of any intervention. Furthermore, such biomarkers can elucidate regeneration mechanisms and open new avenues for research. Without these measures, clinical decision-making falls short, and research becomes more costly, time-consuming, and sometimes infeasible. As a companion to Part 2, which is focused on non-invasive imaging, Part 1 of this two-part scoping review systematically identifies and critically examines many current and emerging neurophysiological techniques that have the potential to evaluate peripheral nerve health, particularly from the perspective of regenerative therapies and research.

A scoping review of current and emerging techniques for evaluation of peripheral nerve health, degeneration and regeneration: part 2, non-invasive imaging.

Peripheral neuroregenerative research and therapeutic options are expanding exponentially. With this expansion comes an increasing need to reliably evaluate and quantify nerve health. Valid and responsive measures of the nerve status are essential for both clinical and research purposes for diagnosis, longitudinal follow-up, and monitoring the impact of any intervention. Furthermore, novel biomarkers can elucidate regenerative mechanisms and open new avenues for research. Without such measures, clinical decision-making is impaired, and research becomes more costly, time-consuming, and sometimes infeasible. Part 1 of this two-part scoping review focused on neurophysiology. In part 2, we identify and critically examine many current and emerging non-invasive imaging techniques that have the potential to evaluate peripheral nerve health, particularly from the perspective of regenerative therapies and research.

Dorsal visual stream is preferentially engaged during externally guided action selection in Parkinson Disease.

OBJECTIVE: In patients with Parkinson Disease (PD), self-initiated or internally cued (IC) actions are thought to be compromised by the disease process, as exemplified by impairments in action initiation. In contrast, externally-cued (EC) actions which are made in response to sensory prompts can restore a remarkable degree of movement capability in PD, particularly alleviating freezing-of-gait. This study investigates the electrophysiological underpinnings of movement facilitation in PD through visuospatial cuing, with particular attention to the dynamics within the posterior parietal cortex (PPC) and lateral premotor cortex (LPMC) axis of the dorsal visual stream. METHODS: Invasive cortical recordings over the PPC and LPMC were obtained during deep brain stimulation lead implantation surgery. Thirteen PD subjects performed an action selection task, which was constituted by left or right joystick movement with directional visual cuing in the EC condition and internally generated direction selection in the IC condition. Time-resolved neural activities within and between the PPC and LPMC were compared between EC and IC conditions. RESULTS: Reaction times (RT) were significantly faster in the EC condition relative to the IC condition (paired t-test, p = 0.0015). PPC-LPMC inter-site phase synchrony within the ß-band (13-35 Hz) was significantly greater in the EC relative to the IC condition. Greater PPC-LPMC ß debiased phase lag index (dwPLI) prior to movement onset was correlated with faster reaction times only in the EC condition. Multivariate granger causality (GC) was greater in the EC condition relative to the IC condition, prior to and during movement. CONCLUSION: Relative to IC actions, we report relative increase in inter-site phase synchrony and directional PPC to LPMC connectivity in the ß-band during preparation and execution of EC actions. Furthermore, increased strength of connectivity is predictive of faster RT, which are pathologically slow in PD patients. Stronger engagement of the PPC-LPMC cortical network by an EC specifically through the channel of ß-modulation is implicated in correcting the pathological slowing of action initiation seen in Parkinson's patients. SIGNIFICANCE: These findings shed light on the electrophysiological mechanisms that underlie motor facilitation in PD patients through visuospatial cuing.

A novel endoscope-assisted technique for lateral lumbar interbody fusion: feasibility study, technical note, and operative video.

The lateral approach to the spine is generally well tolerated, but reports of debilitating injury to the lumbar plexus, iliac vessels, ureter, and abdominal viscera are increasingly recognized, likely related to the lack of direct visualization of these nearby structures. To minimize this complication profile, the authors describe here a novel, minimally invasive, endoscope-assisted technique for the LLIF and evaluate its clinical feasibility. Seven consecutive endoscope-assisted lateral lumbar interbody fusion (LLIF) procedures by the senior authors were reviewed for the incidence of approach-related complications. One patient had a postoperative approach-related complication. This patient developed transient ipsilateral thigh hip flexion weakness that resolved spontaneously by the 3-month follow-up. No patient experienced visceral, urological, or vascular injury, and no patient sustained a permanent neurological injury related to the procedure. The authors' preliminary experience suggests that this endoscope-assisted LLIF technique may be clinically feasible to mitigate vascular, urological, and visceral injury, especially in patients with previous abdominal surgery, anomalous anatomy, and revision operations. It provides direct visualization of at-risk structures without significant additional operative time. A larger series is needed to determine whether it reduces the incidence of lumbar plexopathy or visceral injury compared with traditional lateral approaches.

Current and Expected Advances in Deep Brain Stimulation for Movement Disorders.

Deep brain stimulation (DBS) has become an established treatment for medically refractory movement disorders including Parkinson's disease, essential tremor, and dystonia. The field of DBS continues to evolve with advances in patient selection, target identification, electrode and pulse generator technology, and the development of more effective stimulation paradigms such as closed-loop stimulation. Furthermore, as the safety and efficacy of DBS improves through better hardware design and deeper understanding of its mechanisms of action, the indications for DBS will continue to expand to cover a wider range of disorders. Finally, the recent approval of MR-guided focused ultrasound for the treatment of essential tremor and potentially other movement disorders heralds a resurgence in lesion creation as a viable alternative to DBS for selected patients.

Quantitative Analysis of Metabolic Abnormality Associated with Brain Developmental Venous Anomalies.

BACKGROUND AND PURPOSE: Abnormal hypometabolism is common in the brain parenchyma surrounding developmental venous anomalies (DVAs), although the degree of DVA-associated hypometabolism (DVAAh) has not been quantitatively analyzed. In this study, we demonstrate a simple method for the measurement of DVAAh and test the hypothesis that DVAs are associated with a quantifiable decrement in metabolic activity. MATERIALS AND METHODS: Measurements of DVAAh using ratios of standardized uptake values (SUVs) and comparison to a normal database were performed on a cohort of 25 patients (12 male, 13 female), 14 to 76 years old, with a total of 28 DVAs (20 with DVAAh, seven with isometabolic activity, and one with hypermetabolic activity). RESULTS: Qualitative classification of none, mild, moderate, and severe DVAAh corresponded to quantitative measurements of DVAAh of 1 ± 3%, 12 ± 7%, 18 ± 6%, and 37 ± 6%, respectively. A statistically significant linear correlation between DVAAh and age was observed (P = 0.003), with a 3% reduction in metabolic activity per decade. A statistically significant linear correlation between DVAAh and DVA size was observed (P = 0.01), with a 4% reduction in metabolic activity per each 1 cm in the longest dimension. The SUVDVA-based measures of DVAAh correlated (P = 0.001) with measures derived from comparison with a standardized database. CONCLUSION: We present a simple method for the quantitative measurement of DVAAh using ratios of SUVs, and find that this quantitative analysis is consistent with a qualitative classification. We find that 54% (15 of 28) of DVAs are associated with a greater than 10% decrease in metabolic activity.