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 ß 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 ß 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.

Diversity in Neurosurgical Recruitment and Training in the United States: A Systematic Review.

OBJECTIVE: The benefits of diversity are particularly salient in neurosurgical training because of treatment of varied patient populations and the importance of close collaboration between trainees and attending neurosurgeons of different backgrounds. However, there is a paucity of literature that comprehensively examines diversity in neurosurgical recruitment and training. The aim of this study is to systematically review the scope of diversity in neurosurgical recruitment and training. METHODS: PudMed, Embase, and Scopus were searched since inception to October 31, 2021. Inclusion consisted of 1) on neurosurgery training; 2) sample was medical student, resident, fellows or attending; 3) discussed diversity variable(s). This study followed PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. RESULTS: Of 1578 articles, 15 studies were included. Studies largely reported gender (n = 14) underrepresentation in neurosurgery compared with racial/ethnic diversity (n = 2) and socioeconomic status (n = 1). From studies focusing on residency match (n = 4), women medical students placed greater emphasis on mentorship, earlier clinical exposure, and program camaraderie and reputation as most important. From studies (n = 4) reporting retention and attrition, although women residents and attendings representation has increased, black, indigenous and people of color groups continue to represent <15% of studies on neurosurgical training. Studies (n = 4) discussing research suggested that women residents were more likely to have lower h-indices with fewer research grants. Studies (n = 4) describing workforce employment further showed that women and racial/ethnic minority groups were less likely to hold high academic and leadership positions. In studies (n = 4) on work-life balance, 18.5% women attendings found less career fulfillment and 20.4% would not choose to pursue neurosurgery again because of lack of protected personal time. CONCLUSIONS: This systematic review shows the scope of studies of diversity within neurosurgery and provides impetus for efforts to expand our understanding of diversity within the field.

Democratizing Access to Neurosurgical Medical Education: National Efforts in a Medical Student Training Camp During Coronavirus Disease 2019.

BACKGROUND: National medical student surveys amidst the coronavirus disease 2019 (COVID-19)-driven subinternship cancellations have demonstrated the need for supplemental, standardized subspecialty medical education, mentorship, and career planning nationally. We have presented the first live, cross-institutional virtual medical student subspecialty training camp to deliver standardized neurosurgical educational content to medical students during the COVID-19 pandemic, and its results on medical student anxiety and perceptions of neurosurgery. METHODS: The online training camp used a video conferencing platform that was open to all medical students. A post-training camp survey was administered. RESULTS: A total of 305 medical students registered for the event from 107 unique U.S. medical schools. Of the 305 medical students, 108 reported intending to apply to neurosurgery residency in 2021. The top medical student objectives for the training camp were program networking and mentorship. Of the 305 participants, 121 (39.7%) completed the post-training survey. Of the respondents, 65.0% reported improved neurosurgical knowledge, 79.8% reported decreased anxiety about subinternships and interviews, 82.5% reported increased enthusiasm about neurosurgery, and 100% desired a future annual virtual training camp because of the increased accessibility and decreased cost. This was especially important for students at institutions without home subspecialty programs and those with financial burdens. CONCLUSIONS: COVID-19-driven innovations in medical education have accelerated changes that may have long been necessary. This virtual structure improved resource usage and scalability compared with in-person training, maintained social distancing, and democratized access to standardized, specialized content not often available through traditional medical curricula. Even as a supplement to in-person events, the virtual training camp model could be implemented by national medical societies, which might significantly increase medical students' preparedness for, and education in, neurosurgery and other subspecialties.

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

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.

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.

Subcutaneous sumatriptan: association with decreases in postoperative pain and opioid use after elective cranial surgery.

OBJECTIVE: Sumatriptan, a serotonin receptor agonist, has been used in the management of primary headache disorders and has been shown to affect trigeminal dural afferents. There is limited literature on the safety and efficacy of sumatriptan for postcraniotomy pain management. This study aimed to identify whether subcutaneous sumatriptan is a safe and efficacious pain management strategy after elective craniotomy. METHODS: The authors retrospectively reviewed patients who underwent supratentorial or suboccipital craniotomy between 2016 and 2019 that was performed by a single provider at a single institution to identify patients given subcutaneous sumatriptan in the postoperative period. Pain scores and intravenous and oral opioid use were compared in patients with (n = 15) and without (n = 45) sumatriptan administration. RESULTS: Patients with and without sumatriptan administration had no significant differences in baseline characteristics or surgery type. There were no sumatriptan-related complications. The average pain score decreased from 3.9 to 1.3 within 1 hour after sumatriptan administration (p = 0.014). In both adult and pediatric patients there was decreased postoperative pain (adults: pain score of 1.1 vs 7.1, p < 0.001; pediatric: 1.1 vs 3.9, p = 0.007) within the first 48 hours. There were decreases in intravenous opioid use, length of intravenous opioid use, maximum dose of intravenous opioid used, oral opioid use, length of oral opioid use, and maximum dose of oral opioid used in both adult and pediatric patients. CONCLUSIONS: The authors identified subcutaneous sumatriptan as a safe and efficacious tool for postoperative pain management after craniotomy. Large multicenter randomized controlled studies are needed to further evaluate the specific role of sumatriptan in postoperative pain management after craniotomy.

Mechanical failure of the Mobi-C implant for artificial cervical disc replacement: report of 4 cases.

Cervical spondylosis is one of the most commonly treated conditions in neurosurgery. Increasingly, cervical disc replacement (CDR) has become an alternative to traditional arthrodesis, particularly when treating younger patients. Thus, surgeons continue to gain a greater understanding of short- and long-term complications of arthroplasty. Here, the authors present a series of 4 patients initially treated with Mobi-C artificial disc implants who developed postoperative neck pain. Dynamic imaging revealed segmental kyphosis at the level of the implant. All implants were locked in the flexion position, and all patients required reoperation. This is the first reported case series of symptomatic segmental kyphosis after CDR.

Isocitrate Dehydrogenase Mutations in Low-Grade Gliomas Correlate With Prolonged Overall Survival in Older Patients.

BACKGROUND: Older age has been associated with worse outcomes in low-grade gliomas (LGGs). Given their rarity in the older population, determining optimal treatment plans and patient outcomes remains difficult. OBJECTIVE: To retrospectively study LGG survival outcomes in an older population stratified by molecular genetic profiles. METHODS: We included patients age ≥40 yr with pathologically confirmed World Health Organization grade II gliomas treated at a single institution between 1995 and 2015. We collected tumor genomic information when available. RESULTS: Median overall survival for the entire group (n = 111, median age 51 yr, range 40-77 yr) was 15.75 yr with 5- and 10-yr survival rates of 84.3% and 67.7%, respectively. On univariate analysis, patients with isocitrate dehydrogenase (IDH) mutation had significantly increased survival compared to IDH wildtype (hazard ratio [HR] 0.17 [0.07-0.45], P < .001). Older age, seizure at presentation, larger tumor size, IDH wildtype, biopsy only, chemotherapy, and radiation were significantly associated with shorter survival based on univariate analyses. In patients with known IDH status (n = 73), bivariate analysis of IDH mutation status and age showed only IDH status significantly influenced overall survival (HR 0.22 [0.07-0.68], P = .008). Greater surgical resection was predictive of survival, although extent of resection significantly correlated with IDH mutation status (odds ratio 7.5; P < .001). CONCLUSION: We show that genomic alterations in LGG patients ≥40 occur at high rates like the younger population and predict a similar survival advantage. Maximizing surgical resection may have survival benefit, although feasibility of resection is often linked to IDH status. Given the importance of molecular genetics, a redefinition of prognostic factors associated with these tumors is likely to emerge.

Neuromodulation for substance addiction in human subjects: A review.

Substance abuse is one of the most prevalent and costly health problems in the world today. Standard medical therapy is often not curative, and relapse is common. Research over the past several decades on the neural underpinnings of addiction has implicated a network of structures within the brain shown to be altered in patients with substance abuse. The field of neuromodulation aims to utilize this knowledge to treat dysfunctional circuits by targeting and modulating specific brain circuits. While invasive neuromodulation such as DBS and VNS have proven to be effective in treating movement disorders, OCD and epilepsy, there is increasing interest and data with regards to its potential application for the treatment of severe, intractable addiction. Several neuromodulatory techniques and brain targets are currently under investigation in patients with various substance abuse disorders. This review aims to summarize the current state of evidence for neurosurgical neuromodulation as a therapy for substance abuse and addiction, and to provide additional expert opinions as to the obstacles and future directions of this endeavor.

Mycobacterium abscessus: A Rare Cause of Periprosthetic Knee Joint Infection.

A 61-year-old woman with a periprosthetic knee joint infection caused by Mycobacterium abscessus was successfully treated with surgical débridement, multidrug antimicrobial therapy, and staged reimplantation. To the authors' knowledge, this represents the first report of successfully treating this organism after knee arthroplasty. M. abscessus knee infections are rare, and there are no specific guidelines to inform treatment or successful treatment regimens for periprosthetic knee infections. Medical management alone was not successful in this case and hence cannot be recommended. Using a collaborative multidisciplinary approach, including surgical débridement, staged reimplantation, and multidrug antimicrobials, successful eradication of the periprosthetic joint infection caused by M. abscessus was achieved.