A helium-burning white dwarf binary as a supersoft X-ray source.

Type Ia supernovae are cosmic distance indicators1,2, and the main source of iron in the Universe3,4, but their formation paths are still debated. Several dozen supersoft X-ray sources, in which a white dwarf accretes hydrogen-rich matter from a non-degenerate donor star, have been observed5 and suggested as Type Ia supernovae progenitors6-9. However, observational evidence for hydrogen, which is expected to be stripped off the donor star during the supernova explosion10, is lacking. Helium-accreting white dwarfs, which would circumvent this problem, have been predicted for more than 30 years (refs. 7,11,12), including their appearance as supersoft X-ray sources, but have so far escaped detection. Here we report a supersoft X-ray source with an accretion disk whose optical spectrum is completely dominated by helium, suggesting that the donor star is hydrogen-free. We interpret the luminous and supersoft X-rays as resulting from helium burning near the surface of the accreting white dwarf. The properties of our system provide evidence for extended pathways towards Chandrasekhar-mass explosions based on helium accretion, in particular for stable burning in white dwarfs at lower accretion rates than expected so far. This may allow us to recover the population of the sub-energetic so-called Type Iax supernovae, up to 30% of all Type Ia supernovae13, within this scenario.

Mechanisms and plasticity of chemogenically induced interneuronal suppression of principal cells.

How do firing patterns in a cortical circuit change when inhibitory neurons are excited? We virally expressed an excitatory designer receptor exclusively activated by a designer drug (Gq-DREADD) in all inhibitory interneuron types of the CA1 region of the hippocampus in the rat. While clozapine N-oxide (CNO) activation of interneurons suppressed firing of pyramidal cells, unexpectedly the majority of interneurons also decreased their activity. CNO-induced inhibition decreased over repeated sessions, which we attribute to long-term synaptic plasticity between interneurons and pyramidal cells. Individual interneurons did not display sustained firing but instead transiently enhanced their activity, interleaved with suppression of others. The power of the local fields in the theta band was unaffected, while power at higher frequencies was attenuated, likely reflecting reduced pyramidal neuron spiking. The incidence of sharp wave ripples decreased but the surviving ripples were associated with stronger population firing compared with the control condition. These findings demonstrate that DREADD activation of interneurons brings about both short-term and long-term circuit reorganization, which should be taken into account in the interpretation of chemogenic effects on behavior.

Microscale Physiological Events on the Human Cortical Surface.

Despite ongoing advances in our understanding of local single-cellular and network-level activity of neuronal populations in the human brain, extraordinarily little is known about their "intermediate" microscale local circuit dynamics. Here, we utilized ultra-high-density microelectrode arrays and a rare opportunity to perform intracranial recordings across multiple cortical areas in human participants to discover three distinct classes of cortical activity that are not locked to ongoing natural brain rhythmic activity. The first included fast waveforms similar to extracellular single-unit activity. The other two types were discrete events with slower waveform dynamics and were found preferentially in upper cortical layers. These second and third types were also observed in rodents, nonhuman primates, and semi-chronic recordings from humans via laminar and Utah array microelectrodes. The rates of all three events were selectively modulated by auditory and electrical stimuli, pharmacological manipulation, and cold saline application and had small causal co-occurrences. These results suggest that the proper combination of high-resolution microelectrodes and analytic techniques can capture neuronal dynamics that lay between somatic action potentials and aggregate population activity. Understanding intermediate microscale dynamics in relation to single-cell and network dynamics may reveal important details about activity in the full cortical circuit.

The generation and propagation of the human alpha rhythm.

The alpha rhythm is the longest-studied brain oscillation and has been theorized to play a key role in cognition. Still, its physiology is poorly understood. In this study, we used microelectrodes and macroelectrodes in surgical epilepsy patients to measure the intracortical and thalamic generators of the alpha rhythm during quiet wakefulness. We first found that alpha in both visual and somatosensory cortex propagates from higher-order to lower-order areas. In posterior cortex, alpha propagates from higher-order anterosuperior areas toward the occipital pole, whereas alpha in somatosensory cortex propagates from associative regions toward primary cortex. Several analyses suggest that this cortical alpha leads pulvinar alpha, complicating prevailing theories of a thalamic pacemaker. Finally, alpha is dominated by currents and firing in supragranular cortical layers. Together, these results suggest that the alpha rhythm likely reflects short-range supragranular feedback, which propagates from higher- to lower-order cortex and cortex to thalamus. These physiological insights suggest how alpha could mediate feedback throughout the thalamocortical system.

Time-resolved neural reinstatement and pattern separation during memory decisions in human hippocampus.

Mnemonic decision-making has long been hypothesized to rely on hippocampal dynamics that bias memory processing toward the formation of new memories or the retrieval of old ones. Successful memory encoding may be best optimized by pattern separation, whereby two highly similar experiences can be represented by underlying neural populations in an orthogonal manner. By contrast, successful memory retrieval is thought to be supported by a recovery of the same neural pattern laid down during encoding. Here we examined how hippocampal pattern completion and separation emerge over time during memory decisions. We measured electrocorticography activity in the human hippocampus and posterior occipitotemporal cortex (OTC) while participants performed continuous recognition of items that were new, repeated (old), or highly similar to a prior item (similar). During retrieval decisions of old items, both regions exhibited significant reinstatement of multivariate high-frequency activity (HFA) associated with encoding. Further, the extent of reinstatement of encoding patterns during retrieval was correlated with the strength (HFA power) of hippocampal encoding. Evidence for encoding pattern reinstatement was also seen in OTC on trials requiring fine-grained discrimination of similar items. By contrast, hippocampal activity showed evidence for pattern separation during these trials. Together, these results underscore the critical role of the hippocampus in supporting both reinstatement of overlapping information and separation of similar events.

Somatic SLC35A2 variants in the brain are associated with intractable neocortical epilepsy.

OBJECTIVE: Somatic variants are a recognized cause of epilepsy-associated focal malformations of cortical development (MCD). We hypothesized that somatic variants may underlie a wider range of focal epilepsy, including nonlesional focal epilepsy (NLFE). Through genetic analysis of brain tissue, we evaluated the role of somatic variation in focal epilepsy with and without MCD. METHODS: We identified somatic variants through high-depth exome and ultra-high-depth candidate gene sequencing of DNA from epilepsy surgery specimens and leukocytes from 18 individuals with NLFE and 38 with focal MCD. RESULTS: We observed somatic variants in 5 cases in SLC35A2, a gene associated with glycosylation defects and rare X-linked epileptic encephalopathies. Nonsynonymous variants in SLC35A2 were detected in resected brain, and absent from leukocytes, in 3 of 18 individuals (17%) with NLFE, 1 female and 2 males, with variant allele frequencies (VAFs) in brain-derived DNA of 2 to 14%. Pathologic evaluation revealed focal cortical dysplasia type Ia (FCD1a) in 2 of the 3 NLFE cases. In the MCD cohort, nonsynonymous variants in SCL35A2 were detected in the brains of 2 males with intractable epilepsy, developmental delay, and magnetic resonance imaging suggesting FCD, with VAFs of 19 to 53%; Evidence for FCD was not observed in either brain tissue specimen. INTERPRETATION: We report somatic variants in SLC35A2 as an explanation for a substantial fraction of NLFE, a largely unexplained condition, as well as focal MCD, previously shown to result from somatic mutation but until now only in PI3K-AKT-mTOR pathway genes. Collectively, our findings suggest a larger role than previously recognized for glycosylation defects in the intractable epilepsies. Ann Neurol 2018.

Human Dorsolateral Prefrontal Cortex Is Not Necessary for Spatial Working Memory.

A dominant theory, based on electrophysiological and lesion evidence from nonhuman primate studies, posits that the dorsolateral prefrontal cortex (dlPFC) stores and maintains working memory (WM) representations. Yet, neuroimaging studies have consistently failed to translate these results to humans; these studies normally find that neural activity persists in the human precentral sulcus (PCS) during WM delays. Here, we attempt to resolve this discrepancy. To test the degree to which dlPFC is necessary for WM, we compared the performance of patients with dlPFC lesions and neurologically healthy controls on a memory-guided saccade task that was used in the monkey studies to measure spatial WM. We found that dlPFC damage only impairs the accuracy of memory-guided saccades if the damage impacts the PCS; lesions to dorsolateral dlPFC that spare the PCS have no effect on WM. These results identify the necessary subregion of the frontal cortex for WM and specify how this influential animal model of human cognition must be revised.

Human parietal cortex lesions impact the precision of spatial working memory.

The neural mechanisms that support working memory (WM) depend on persistent neural activity. Within topographically organized maps of space in dorsal parietal cortex, spatially selective neural activity persists during WM for location. However, to date, the necessity of these topographic subregions of human parietal cortex for WM remains unknown. To test the causal relationship of these areas to WM, we compared the performance of patients with lesions to topographically organized parietal cortex with those of controls on a memory-guided saccade (MGS) task as well as a visually guided saccade (VGS) task. The MGS task allowed us to measure WM precision continuously with great sensitivity, whereas the VGS task allowed us to control for any deficits in general spatial or visuomotor processing. Compared with controls, patients generated memory-guided saccades that were significantly slower and less accurate, whereas visually guided saccades were unaffected. These results provide key missing evidence for the causal role of topographic areas in human parietal cortex for WM, as well as the neural mechanisms supporting WM.

Multicenter experience using simeprevir and sofosbuvir with or without ribavirin to treat hepatitis C genotype 1 after liver transplant.

UNLABELLED: Treatment with an all-oral interferon-free antiviral regimen using simeprevir and sofosbuvir with or without ribavirin (RBV) for 12 weeks resulted in high sustained virologic response (SVR) rates along with minimal adverse events in non-liver transplant (LT) patients with hepatitis C virus (HCV) genotype 1 infection. This is the first multicenter report on the efficacy, safety, and tolerability of this regimen in LT recipients. A total of 123 patients (76% male, 74% white, 60% genotype 1a, 30% METAVIR F3-F4, 4% decompensation, 11% cholestatic recurrence, 7% had kidney transplant, and 82% previously failed pegylated interferon/RBV-based regimens) received treatment and were followed for a median of 30 weeks (range 12-53 weeks). The median time from LT to treatment was 32 months (range 2-317 months). Tacrolimus was the primary immunosuppression in 91% of patients. Minimal immunosuppression dose adjustments were required. An SVR 12 weeks after treatment completion (SVR12) was achieved in 90% of patients (95% confidence interval 84%-96%). In patients with genotype 1a infection, the SVR12 rate was significantly lower in those with METAVIR F3-F4 (71%) compared to those with F0-F2 (91%). Half of the patients achieved undetected HCV RNA at treatment week 4, and their SVR12 rate was significantly higher (96%) compared to those with detectable HCV RNA (83%). Treatment was very well tolerated with mild degrees of adverse events, except for one death possibly due to drug-induced lung injury. In the 25 patients who received RBV, 72% developed anemia requiring intervention. CONCLUSION: An all-oral interferon-free antiviral regimen using simeprevir and sofosbuvir with or without RBV for 12 weeks was very well tolerated and resulted in excellent SVR12 rates in LT recipients with HCV genotype 1 infection.

Multicenter experience using simeprevir and sofosbuvir with or without ribavirin to treat hepatitis C genotype 1 in patients with cirrhosis.

UNLABELLED: Interferon (IFN)-free regimens are needed to treat hepatitis C virus (HCV) infection. Combined simeprevir (SMV) and sofosbuvir (SOF) with or without ribavirin (RBV) results in high sustained virological response (SVR) rates along with minimal adverse events (AEs) in patients with hepatitis C genotype 1 (HCV GT1). The aim of this study was to report on the virological response, safety, and tolerability of SOF and SMV with or without RBV in compensated and decompensated patients with cirrhosis with HCV GT1 infection. Patients treated with standardized clinical protocol utilizing SMV+SOF with or without RBV at three transplant centers were retrospectively reviewed. A total of 119 patients (61% male, 87% white, 69% subtype 1a, 30% Child-Pugh-Turcott [CPT]-B liver cirrhosis [LC], and 82% were treatment experienced) received treatment and were followed for a median of 38 weeks (range, 12-58). Sustained virological response (SVR) at week 12 (SVR12) was achieved in 78% (92 of 118) of patients (95% confidence interval: 69-85). Lower pretreatment Model for End Stage Liver Disease (MELD) score was a predictor of SVR12 (P = 0.018). Baseline viral load, previous treatment status, RBV use, or GT1 subtype did not impact SVR 12. The majority of patients with SVR12 showed stability or improvement in MELD score. Treatment was very well tolerated with mild degrees of AEs. CONCLUSIONS: The regimen of SMV+SOF with or without RBV for 12 weeks was very well tolerated and resulted in high SVR12 rates (78%) in HCV GT1 patients with LC. SVR12 was inversely related to pretreatment MELD. SVR12 had favorable short-term impact on MELD score. Long-term impact on disease stability is yet to be determined. Longer treatment duration or the use of different regimen may still be needed in this population.

The association between childhood maltreatment, psychopathology, and adult sexual victimization in men and women: results from three independent samples.

BACKGROUND: Childhood maltreatment (CM) has consistently been linked with adverse outcomes including substance use disorders and adult sexual revictimization. Adult sexual victimization itself has been linked with psychopathology but has predominately been studied in women. The current investigation examines the impact of CM and co-occurring psychopathology on adult sexual victimization in men and women, replicating findings in three distinct samples. METHOD: We investigated the association between continuous CM factor scores and adult sexual victimization in the Childhood Trauma Study (CTS) sample (N = 2564). We also examined the unique relationship between childhood sexual abuse (CSA) and adult sexual victimization while adjusting for co-occurring substance dependence and psychopathology. We replicated these analyses in two additional samples: the Comorbidity and Trauma Study (CATS; N = 1981) and the Australian Twin-Family Study of Alcohol Use Disorders (OZ-ALC; N = 1537). RESULTS: Analyses revealed a significant association with CM factor scores and adult sexual victimization for both men and women across all three samples. The CSA factor score was strongly associated with adult sexual victimization after adjusting for substance dependence and psychopathology; higher odds ratios were observed in men (than women) consistently across the three samples. CONCLUSIONS: A continuous measure of CSA is independently associated with adult sexual trauma risk across samples in models that included commonly associated substance dependence and psychopathology as covariates. The strength of the association between this CSA measure and adult sexual victimization is higher in magnitude for men than women, pointing to the need for further investigation of sexual victimization in male community samples.

Emerging technologies to measure neighborhood conditions in public health: implications for interventions and next steps.

Adverse neighborhood conditions play an important role beyond individual characteristics. There is increasing interest in identifying specific characteristics of the social and built environments adversely affecting health outcomes. Most research has assessed aspects of such exposures via self-reported instruments or census data. Potential threats in the local environment may be subject to short-term changes that can only be measured with more nimble technology. The advent of new technologies may offer new opportunities to obtain geospatial data about neighborhoods that may circumvent the limitations of traditional data sources. This overview describes the utility, validity and reliability of selected emerging technologies to measure neighborhood conditions for public health applications. It also describes next steps for future research and opportunities for interventions. The paper presents an overview of the literature on measurement of the built and social environment in public health (Google Street View, webcams, crowdsourcing, remote sensing, social media, unmanned aerial vehicles, and lifespace) and location-based interventions. Emerging technologies such as Google Street View, social media, drones, webcams, and crowdsourcing may serve as effective and inexpensive tools to measure the ever-changing environment. Georeferenced social media responses may help identify where to target intervention activities, but also to passively evaluate their effectiveness. Future studies should measure exposure across key time points during the life-course as part of the exposome paradigm and integrate various types of data sources to measure environmental contexts. By harnessing these technologies, public health research can not only monitor populations and the environment, but intervene using novel strategies to improve the public health.

Acute liver failure associated with Garcinia cambogia use.

Millions of Americans regularly use herbal supplements, but many are unaware of the potential hidden dangers. Numerous supplements have been associated with hepatotoxicity and, indeed dietary/herbal supplements represent an increasingly common source of acute liver injury. We report a case of acute liver failure requiring liver transplantation associated with the use of Garcinia cambogia, a supplement widely promoted for weight loss. When patients present with acute hepatitis or liver failure from an unknown etiology, a careful history of supplement use should be performed.

The corpus callosum and recovery of working memory after epilepsy surgery.

OBJECTIVE: For patients with medically intractable focal epilepsy, the benefit of epilepsy surgery must be weighed against the risk of cognitive decline. Clinical factors such as age and presurgical cognitive level partially predict cognitive outcome; yet, little is known about the role of cross-hemispheric white matter pathways in supporting postsurgical recovery of cognitive function. The purpose of this study is to determine whether the presurgical corpus callosum (CC) midsagittal area is associated with pre- to postsurgical change following epilepsy surgery. METHODS: In this observational study, we retrospectively identified 24 adult patients from an epilepsy resection series who completed preoperative high-resolution T1 -weighted magnetic resonance imaging (MRI) scans, as well as pre- and postsurgical neuropsychological testing. The total area and seven subregional areas of the CC were measured on the midsagittal MRI slice using an automated method. Standardized indices of auditory-verbal working memory and delayed memory were used to probe cognitive change from pre- to postsurgery. CC total and subregional areas were regressed on memory-change scores, after controlling for overall brain volume, age, presurgical memory scores, and duration of epilepsy. RESULTS: Patients had significantly reduced CC area relative to healthy controls. We found a positive relationship between CC area and change in working memory, but not delayed memory; specifically, the larger the CC, the greater the postsurgical improvement in working memory (ß = 0.523; p = 0.009). Effects were strongest in posterior CC subregions. There was no relationship between CC area and presurgical memory scores. SIGNIFICANCE: Findings indicate that larger CC area, measured presurgically, is related to improvement in working memory abilities following epilepsy surgery. This suggests that transcallosal pathways may play an important, yet little understood, role in postsurgical recovery of cognitive functions.

Evidence for flow from hydrodynamic simulations of p-Pb collisions at 5.02 TeV from v2 mass splitting.

We show that a fluid dynamical scenario, already well tested against identified particle p(t) spectra, describes quantitatively the observed mass splitting of the elliptical flow coefficients v(2) for pions and protons. This provides a strong argument in favor of the existence of a fluid dynamical expansion in p-Pb collisions at 5.02 TeV.

A modified laparoscopic hernioplasty (TAPP) is the standard procedure for inguinal and femoral hernias: a retrospective 17-year analysis with 1,123 hernia repairs.

BACKGROUND: Laparoscopic and endoscopic procedures generally are accepted for repair of primary and recurrent hernias that follow conventional (anterior) repair. This report discusses transabdominal preperitoneal (TAPP) for incarcerated hernias, scrotal hernias, and hernias after radical prostatectomy, as well as hernia recurrences after TAPP and totally extraperitoneal (TEP) procedures (complex hernias). Studies with long-term results of hernia recurrences are missing. This study aimed to determine hernia recurrence rates for adults after a modified TAPP procedure. The records of patients who had hernia repair surgery at a general hospital 2, 7, 12, and 17 years earlier were analyzed. Living patients were requested to complete a questionnaire to complement information from their hospital records. METHODS: A retrospective analysis was undertaken that included 5,764 patients who had undergone hernia repair surgery 2-17 years earlier at a single large center. Between 1993 and 2009, a modified TAPP procedure was performed for 5,764 patients (median age, 59.1 years) to repair 6,776 hernias (93.9% of all hernia repairs), including 6,126 primary hernias (87.4%) and 884 recurrent hernias (12.6%). These included 994 complicated hernias (14.2%) closed by a modified TAPP (89.3% of all femoral hernias, 85.9% of scrotal hernias, 79.1% of incarcerated hernias, and 92.7% of hernias after radical prostatectomy). Limited financial and staff resources did not permit a quantitative follow-up study within a reasonable time of all 5,764 patients who had hernia surgery 2-18 years earlier. To obtain quantitative results of hernia recurrences after a modified TAPP, the patients were divided into four subgroups and requested to complete a questionnaire. These four patient subgroups whose surgeries had been performed 2 years earlier (241 patients with 277 hernias), 7 years earlier (285 patients with 376 hernias), 12 years earlier (401 patients with 544 hernias), and 17 years earlier (181 patients with 222 hernias) represented the complete group of hernia sufferers. Patients with symptoms after hernia surgery (n = 5) were invited for a medical checkup by a specialist in hernia surgery at our outpatient unit. RESULTS: The sex, age, and the number of complex hernias of the patients did not differ significantly among the four patient subgroups or in comparison with the entire group. The patients who had received surgery in 1994, 1999, 2004, and 2009 were quizzed by a questionnaire and represented all patients who had hernia surgery from 1993 to 2009. The follow-up response of the living patients in each of the subgroups ranged from 89.5% of those who had hernia surgery 17 years earlier to 95.9% of those who had surgery 2 years earlier. The primary end point of the study was the hernia recurrence rate after a modified TAPP for primary, recurrent, and complex hernias performed 2, 7, 12, and 17 years earlier. The secondary end points of the study focused on the following questions: Is a modified TAPP practicable with acceptable recurrence rates for complex hernias? Do relapse rates show individual surgeon-dependent differences in relation to the learning curve? How many years of postoperative follow-up evaluation are required to determine quantitative recurrence rates (>90% recurrence)? All inguinal and femoral hernias were repaired with a modified TAPP procedure. Hernia defects larger than 1 × 1 cm were closed with nonabsorbable sutures before the mesh was implanted. Within 17 years after surgery, 4 (4.3%) of the 94 study participants treated with a modified TAPP procedure for primary or recurrent inguinal and femoral hernias experienced recurrent hernias (4 recurrences after 117 hernioplasties, 3.4%). Within 12 years after surgery, 4 (1 %) of 302 patients experienced recurrent hernias (4 recurrences after 398 modified TAPP procedures, 1%). Within 7 years after surgery for inguinal or femoral hernias, 8 (3.2%) of 251 patients had relapsed (8 recurrences after 337 modified TAPP procedures, 2.4%). Within 2 years after a modified TAPP, only 1 of 230 patients (0.4%) experienced a recurrent hernia (1 relapse after 265 hernioplasties, 0.4%). After the modified TAPP procedure, 52.9% (n = 9) of the patients with a recurrent hernia had a second repair at our hospital, and 35.3% (n = 6) had the second repair at other hospitals, whereas 2 patients (11.8 %) renounced a repeat surgical intervention. The recurrence rate after a modified TAPP procedure for all the patients (n = 896) was 1.8%. The study participants with primary hernias (n = 765) had a 1.7% recurrence rate, whereas the rate for recurrent hernias after anterior repair (n = 131) was 2.3 %. Incarcerated hernias (n = 47) and hernias after radical prostatectomy (n = 22) that were closed by the modified TAPP procedure resulted in no hernia recurrences. Only 1 of 47 patients with scrotal hernias had a hernia relapse. Of all the hernia recurrences between 1993 and 2009 (n = 76), 60.5% (n = 46) developed within 2 years after surgery, whereas 15.8% (n = 12) occurred after more than 5 years, and 4% (n = 3) occurred after more than 10 years. The recurrence rates also were higher for surgeons in the early period after completion of their personal learning curves (<50 modified TAPP procedures performed on their own responsibility). CONCLUSIONS: In a retrospective long-term study (2-17 years) from a single center with 1,108 patients and 1,123 modified TAPP procedures (93.9% of all hernia repairs), the hernia recurrence rate was 1.7% for adults with primary hernias (n = 765 patients) and 2.3% for adults with recurrent hernias after anterior repair (n = 131 patients). A modified TAPP procedure with suturing of hernia defects larger than 1 × 1 cm can be used as the standard procedure without recurrences for femoral hernias, incarcerated hernias, and hernias after radical prostatectomy, with low recurrence rates for scrotal hernias (2%). To collect quantitative data on hernia recurrence rates, postoperative follow-up studies longer than 10 years are needed (4% of recurrences developed later than 10 years after surgery).

Quantification of GTPase Cycling Rates of GTPases and GTPase:Effector Mixtures Using GTPase Glo Assays.

In different cellular activities such as signal transduction, cell division, and intracellular transportation, small guanosine triphosphatases (GTPases) take on a vital role. Their function involves hydrolysis of guanosine triphosphate (GTP) to guanosine diphosphate (GDP). In this article, we explain the application of a commercially available GTPase assay-the GTPase Glo assay by Promega-for investigation of GTPase-effector interactions. We provide experimental protocols together with an analysis model and software to obtain GTPase cycling rates of GTPases and GTPase:effector mixtures. GTPase cycling rates refer to the rates by which a GTPase completes an entire GTPase cycle. These rates enable quantification of the strength of GTPase effectors in a concentration-dependent fashion, as well as quantification of the combined effect of two effectors, independent of which GTPase cycle step they are affecting. © 2024 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol: Conducting GTPase Glo assays Support Protocol 1: Analyzing GTPase assays to correlate luminescence with remaining GTP Support Protocol 2: Fitting GTPase assay data to obtain GTPase cycling rates.

Timing and location of speech errors induced by direct cortical stimulation.

Cortical regions supporting speech production are commonly established using neuroimaging techniques in both research and clinical settings. However, for neurosurgical purposes, structural function is routinely mapped peri-operatively using direct electrocortical stimulation. While this method is the gold standard for identification of eloquent cortical regions to preserve in neurosurgical patients, there is lack of specificity of the actual underlying cognitive processes being interrupted. To address this, we propose mapping the temporal dynamics of speech arrest across peri-sylvian cortices by quantifying the latency between stimulation and speech deficits. In doing so, we are able to substantiate hypotheses about distinct region-specific functional roles (e.g., planning versus motor execution). In this retrospective observational study, we analyzed 20 patients (12 female; age range 14-43) with refractory epilepsy who underwent continuous extra-operative intracranial EEG monitoring of an automatic speech task during clinical bedside language mapping. Latency to speech arrest was calculated as time from stimulation onset to speech arrest onset, controlling for individual speech rate. Most instances of motor-based arrest (87.5% of 96 instances) were in sensorimotor cortex with mid-range latencies to speech arrest with a distributional peak at 0.47 seconds. Speech arrest occurred in numerous regions, with relatively short latencies in supramarginal gyrus (0.46 seconds), superior temporal gyrus (0.51 seconds), and middle temporal gyrus (0.54 seconds), followed by relatively long latencies in sensorimotor cortex (0.72 seconds) and especially long latencies in inferior frontal gyrus (0.95 seconds). Nonparametric testing for speech arrest revealed that region predicted latency; latencies in supramarginal gyrus and in superior temporal gyrus were shorter than in sensorimotor cortex and in inferior frontal gyrus. Sensorimotor cortex is primarily responsible for motor-based arrest. Latencies to speech arrest in supramarginal gyrus and superior temporal gyrus (and to a lesser extent middle temporal gyrus) align with latencies to motor-based arrest in sensorimotor cortex. This pattern of relatively quick cessation of speech suggests that stimulating these regions interferes with the outgoing motor execution. In contrast, the latencies to speech arrest in inferior frontal gyrus and in ventral regions of sensorimotor cortex were significantly longer than those in temporoparietal regions. Longer latencies in the more frontal areas (including inferior frontal gyrus and ventral areas of precentral gyrus and postcentral gyrus) suggest that stimulating these areas interrupts a higher-level speech production process involved in planning. These results implicate the ventral specialization of sensorimotor cortex (including both precentral and postcentral gyri) for speech planning above and beyond motor execution.

A low-activity cortical network selectively encodes syntax.

Syntax, the abstract structure of language, is a hallmark of human cognition. Despite its importance, its neural underpinnings remain obscured by inherent limitations of non-invasive brain measures and a near total focus on comprehension paradigms. Here, we address these limitations with high-resolution neurosurgical recordings (electrocorticography) and a controlled sentence production experiment. We uncover three syntactic networks that are broadly distributed across traditional language regions, but with focal concentrations in middle and inferior frontal gyri. In contrast to previous findings from comprehension studies, these networks process syntax mostly to the exclusion of words and meaning, supporting a cognitive architecture with a distinct syntactic system. Most strikingly, our data reveal an unexpected property of syntax: it is encoded independent of neural activity levels. We propose that this "low-activity coding" scheme represents a novel mechanism for encoding information, reserved for higher-order cognition more broadly.

Timing and location of speech errors induced by direct cortical stimulation.

Cortical regions supporting speech production are commonly established using neuroimaging techniques in both research and clinical settings. However, for neurosurgical purposes, structural function is routinely mapped peri-operatively using direct electrocortical stimulation. While this method is the gold standard for identification of eloquent cortical regions to preserve in neurosurgical patients, there is lack of specificity of the actual underlying cognitive processes being interrupted. To address this, we propose mapping the temporal dynamics of speech arrest across peri-sylvian cortices by quantifying the latency between stimulation and speech deficits. In doing so, we are able to substantiate hypotheses about distinct region-specific functional roles (e.g. planning versus motor execution). In this retrospective observational study, we analysed 20 patients (12 female; age range 14-43) with refractory epilepsy who underwent continuous extra-operative intracranial EEG monitoring of an automatic speech task during clinical bedside language mapping. Latency to speech arrest was calculated as time from stimulation onset to speech arrest onset, controlling for individual speech rate. Most instances of motor-based arrest (87.5% of 96 instances) were in sensorimotor cortex with mid-range latencies to speech arrest with a distributional peak at 0.47 s. Speech arrest occurred in numerous regions, with relatively short latencies in supramarginal gyrus (0.46 s), superior temporal gyrus (0.51 s) and middle temporal gyrus (0.54 s), followed by relatively long latencies in sensorimotor cortex (0.72 s) and especially long latencies in inferior frontal gyrus (0.95 s). Non-parametric testing for speech arrest revealed that region predicted latency; latencies in supramarginal gyrus and in superior temporal gyrus were shorter than in sensorimotor cortex and in inferior frontal gyrus. Sensorimotor cortex is primarily responsible for motor-based arrest. Latencies to speech arrest in supramarginal gyrus and superior temporal gyrus (and to a lesser extent middle temporal gyrus) align with latencies to motor-based arrest in sensorimotor cortex. This pattern of relatively quick cessation of speech suggests that stimulating these regions interferes with the outgoing motor execution. In contrast, the latencies to speech arrest in inferior frontal gyrus and in ventral regions of sensorimotor cortex were significantly longer than those in temporoparietal regions. Longer latencies in the more frontal areas (including inferior frontal gyrus and ventral areas of precentral gyrus and postcentral gyrus) suggest that stimulating these areas interrupts a higher-level speech production process involved in planning. These results implicate the ventral specialization of sensorimotor cortex (including both precentral and postcentral gyri) for speech planning above and beyond motor execution.