An increase of inhibition drives the developmental decorrelation of neural activity

Throughout development, the brain transits from early highly synchronous activity patterns to a mature state with sparse and decorrelated neural activity, yet the mechanisms underlying this process are poorly understood. The developmental transition has important functional consequences, as the latter state is thought to allow for more efficient storage, retrieval, and processing of information. Here, we show that, in the mouse medial prefrontal cortex (mPFC), neural activity during the first two postnatal weeks decorrelates following specific spatial patterns. This process is accompanied by a concomitant tilting of excitation-inhibition (E-I) ratio toward inhibition. Using optogenetic manipulations and neural network modeling, we show that the two phenomena are mechanistically linked, and that a relative increase of inhibition drives the decorrelation of neural activity. Accordingly, in mice mimicking the etiology of neurodevelopmental disorders, subtle alterations in E-I ratio are associated with specific impairments in the correlational structure of spike trains. Finally, capitalizing on EEG data from newborn babies, we show that an analogous developmental transition takes place also in the human brain. Thus, changes in E-I ratio control the (de)correlation of neural activity and, by these means, its developmental imbalance might contribute to the pathogenesis of neurodevelopmental disorders.

Coupling of pupil- and neuronal population dynamics reveals diverse influences of arousal on cortical processing

Fluctuations in arousal, controlled by subcortical neuromodulatory systems, continuously shape cortical state, with profound consequences for information processing. Yet, how arousal signals influence cortical population activity in detail has so far only been characterized for a few selected brain regions. Traditional accounts conceptualize arousal as a homogeneous modulator of neural population activity across the cerebral cortex. Recent insights, however, point to a higher specificity of arousal effects on different components of neural activity and across cortical regions. Here, we provide a comprehensive account of the relationships between fluctuations in arousal and neuronal population activity across the human brain. Exploiting the established link between pupil size and central arousal systems, we performed concurrent magnetoencephalographic (MEG) and pupillographic recordings in a large number of participants, pooled across three laboratories. We found a cascade of effects relative to the peak timing of spontaneous pupil dilations: Decreases in low-frequency (2-8 Hz) activity in temporal and lateral frontal cortex, followed by increased high-frequency (>64 Hz) activity in mid-frontal regions, followed by monotonic and inverted U relationships with intermediate frequency-range activity (8-32 Hz) in occipito-parietal regions. Pupil-linked arousal also coincided with widespread changes in the structure of the aperiodic component of cortical population activity, indicative of changes in the excitation-inhibition balance in underlying microcircuits. Our results provide a novel basis for studying the arousal modulation of cognitive computations in cortical circuits.

Circuit mechanisms for the chemical modulation of cortex-wide network interactions and behavioral variability

Influential theories postulate distinct roles of catecholamines and acetylcholine in cognition and behavior. However, previous physiological work reported similar effects of these neuromodulators on the response properties (specifically, the gain) of individual cortical neurons. Here, we show a double dissociation between the effects of catecholamines and acetylcholine at the level of large-scale interactions between cortical areas in humans. A pharmacological boost of catecholamine levels increased cortex-wide interactions during a visual task, but not rest. An acetylcholine boost decreased interactions during rest, but not task. Cortical circuit modeling explained this dissociation by differential changes in two circuit properties: the local excitation-inhibition balance (more strongly increased by catecholamines) and intracortical transmission (more strongly reduced by acetylcholine). The inferred catecholaminergic mechanism also predicted noisier decision-making, which we confirmed for both perceptual and value-based choice behavior. Our work highlights specific circuit mechanisms for shaping cortical network interactions and behavioral variability by key neuromodulatory systems.

Neuronal timescales are functionally dynamic and shaped by cortical microarchitecture

Complex cognitive functions such as working memory and decision-making require information maintenance over seconds to years, from transient sensory stimuli to long-term contextual cues. While theoretical accounts predict the emergence of a corresponding hierarchy of neuronal timescales, direct electrophysiological evidence across the human cortex is lacking. Here, we infer neuronal timescales from invasive intracranial recordings. Timescales increase along the principal sensorimotor-to-association axis across the entire human cortex, and scale with single-unit timescales within macaques. Cortex-wide transcriptomic analysis shows direct alignment between timescales and expression of excitation- and inhibition-related genes, as well as genes specific to voltage-gated transmembrane ion transporters. Finally, neuronal timescales are functionally dynamic: prefrontal cortex timescales expand during working memory maintenance and predict individual performance, while cortex-wide timescales compress with aging. Thus, neuronal timescales follow cytoarchitectonic gradients across the human cortex and are relevant for cognition in both short and long terms, bridging microcircuit physiology with macroscale dynamics and behavior.

Comparison of a Complete Percutaneous Versus Surgical Approach to Aortic Valve Replacement and Revascularization in Patients at Intermediate Surgical Risk: Results From the Randomized SURTAVI Trial

BACKGROUND

For patients with severe aortic stenosis and coronary artery disease, the completely percutaneous approach to aortic valve replacement and revascularization has not been compared with the standard surgical approach.

METHODS

The prospective SURTAVI trial (Safety and Efficiency Study of the Medtronic CoreValve System in the Treatment of Severe, Symptomatic Aortic Stenosis in Intermediate Risk Subjects Who Need Aortic Valve Replacement) enrolled intermediate-risk patients with severe aortic stenosis from 87 centers in the United States, Canada, and Europe between June 2012 and June 2016. Complex coronary artery disease with SYNTAX score (Synergy Between PCI with Taxus and Cardiac Surgery Trial) >22 was an exclusion criterion. Patients were stratified according to the need for revascularization and then randomly assigned to treatment with transcatheter aortic valve replacement (TAVR) or surgical aortic valve replacement (SAVR). Patients assigned to revascularization in the TAVR group underwent percutaneous coronary intervention, whereas those in the SAVR group had coronary artery bypass grafting. The primary end point was the rate of all-cause mortality or disabling stroke at 2 years.

RESULTS

Of 1660 subjects with attempted aortic valve implants, 332 (20%) were assigned to revascularization. They had a higher Society of Thoracic Surgeons risk score for mortality (4.8±1.7% versus 4.4±1.5%; P<0.01) and were more likely to be male (65.1% versus 54.2%; P<0.01) than the 1328 patients not assigned to revascularization. After randomization to treatment, there were 169 patients undergoing TAVR and percutaneous coronary intervention, 163 patients undergoing SAVR and coronary artery bypass grafting, 695 patients undergoing TAVR, and 633 patients undergoing SAVR. No significant difference in the rate of the primary end point was found between TAVR and percutaneous coronary intervention and SAVR and coronary artery bypass grafting (16.0%; 95% CI, 11.1-22.9 versus 14.0%; 95% CI, 9.2-21.1; P=0.62), or between TAVR and SAVR (11.9%; 95% CI, 9.5-14.7 versus 12.3%; 95% CI, 9.8-15.4; P=0.76).

CONCLUSIONS

For patients at intermediate surgical risk with severe aortic stenosis and noncomplex coronary artery disease (SYNTAX score ≤22), a complete percutaneous approach of TAVR and percutaneous coronary intervention is a reasonable alternative to SAVR and coronary artery bypass grafting.

CLINICAL TRIAL REGISTRATION

URL: https://www.

CLINICALTRIALS

gov. Unique identifier: NCT01586910.

Brainstem Modulation of Large-Scale Intrinsic Cortical Activity Correlations

Brain activity fluctuates continuously, even in the absence of changes in sensory input or motor output. These intrinsic activity fluctuations are correlated across brain regions and are spatially organized in macroscale networks. Variations in the strength, topography, and topology of correlated activity occur over time, and unfold upon a backbone of long-range anatomical connections. Subcortical neuromodulatory systems send widespread ascending projections to the cortex, and are thus ideally situated to shape the temporal and spatial structure of intrinsic correlations. These systems are also the targets of the pharmacological treatment of major neurological and psychiatric disorders, such as Parkinson's disease, depression, and schizophrenia. Here, we review recent work that has investigated how neuromodulatory systems shape correlations of intrinsic fluctuations of large-scale cortical activity. We discuss studies in the human, monkey, and rodent brain, with a focus on non-invasive recordings of human brain activity. We provide a structured but selective overview of this work and distil a number of emerging principles. Future efforts to chart the effect of specific neuromodulators and, in particular, specific receptors, on intrinsic correlations may help identify shared or antagonistic principles between different neuromodulatory systems. Such principles can inform models of healthy brain function and may provide an important reference for understanding altered cortical dynamics that are evident in neurological and psychiatric disorders, potentially paving the way for mechanistically inspired biomarkers and individualized treatments of these disorders.

Outcomes in the Randomized CoreValve US Pivotal High Risk Trial in Patients With a Society of Thoracic Surgeons Risk Score of 7% or Less

Importance

Transcatheter aortic valve replacement (TAVR) is now a well-accepted alternative to surgical AVR (SAVR) for patients with symptomatic aortic stenosis at increased operative risk. There is interest in whether TAVR would benefit patients at lower risk.

Objective

The Society of Thoracic Surgeons Predicted Risk of Mortality (STS PROM) has trended downward in US TAVR trials and the STS/American College of Cardiology Transcatheter Valve Therapy Registry. We hypothesized that if the Society of Thoracic Surgeons Predicted Risk of Mortality (STS PROM) alone is sufficient to define decreased risk, the contribution to survival based on the degree of invasiveness of the TAVR procedure will decrease, making it more difficult to show improved survival and benefit over SAVR.

Design, Setting, and Participants

The CoreValve US Pivotal High Risk Trial was a multicenter, randomized, noninferiority trial. This retrospective analysis evaluated patients who underwent an attempted implant and had an STS PROM of 7% or less. The trial was performed at 45 US sites. Patients had severe aortic stenosis and were at increased surgical risk based on their STS PROM score and other risk factors.

Interventions

Eligible patients were randomly assigned (1:1) to self-expanding TAVR or to SAVR.

Main Outcomes and Measures

We retrospectively stratified patients by the overall median STS PROM score (7%) and analyzed clinical outcomes and quality of life using the Kansas City Cardiomyopathy Questionnaire in patients with an STS PROM score of 7% or less.

Results

The mean (SD) ages were 81.5 (7.6) years for the TAVR group and 81.2 years (6.6) for the SAVR group. A little more than half were men (57.9% in the TAVR group and 55.8% in the SAVR group). Of 750 patients who underwent attempted implantation, 383 (202 TAVR and 181 SAVR) had an STS PROM of 7% or less (median [interquartile range]: TAVR, 5.3% [4.3%-6.1%]; SAVR, 5.3% [4.1%-5.9%]). Two-year all-cause mortality for TAVR vs SAVR was 15.0% (95% CI, 8.9-10.0) vs 26.3% (95% CI, 19.7-33.0) (log rank P = .01). The 2-year rate of stroke for TAVR vs SAVR was 11.3% vs 15.1% (log rank P = .50). Quality of life by the Kansas City Cardiomyopathy Questionnaire summary score showed significant and equivalent increases in both groups at 2 years (mean [SD] TAVR, 20.0 [25.0]; SAVR, 18.6 [23.6]; P = .71; both P < .001 compared with baseline). Medical benefit, defined as alive with a Kansas City Cardiomyopathy Questionnaire summary score of at least 60 and a less than 10-point decrease from baseline, was similar between groups at 2 years (TAVR, 51.0%; SAVR, 44.4%; P = .28).

Conclusions and Relevance

Self-expanding TAVR compares favorably with SAVR in high-risk patients with STS PROM scores traditionally considered intermediate risk.

Trial Registration

Clinicaltrials.gov Identifier: NCT01240902.

Catecholamines alter the intrinsic variability of cortical population activity and perception

The ascending modulatory systems of the brain stem are powerful regulators of global brain state. Disturbances of these systems are implicated in several major neuropsychiatric disorders. Yet, how these systems interact with specific neural computations in the cerebral cortex to shape perception, cognition, and behavior remains poorly understood. Here, we probed into the effect of two such systems, the catecholaminergic (dopaminergic and noradrenergic) and cholinergic systems, on an important aspect of cortical computation: its intrinsic variability. To this end, we combined placebo-controlled pharmacological intervention in humans, recordings of cortical population activity using magnetoencephalography (MEG), and psychophysical measurements of the perception of ambiguous visual input. A low-dose catecholaminergic, but not cholinergic, manipulation altered the rate of spontaneous perceptual fluctuations as well as the temporal structure of "scale-free" population activity of large swaths of the visual and parietal cortices. Computational analyses indicate that both effects were consistent with an increase in excitatory relative to inhibitory activity in the cortical areas underlying visual perceptual inference. We propose that catecholamines regulate the variability of perception and cognition through dynamically changing the cortical excitation-inhibition ratio. The combined readout of fluctuations in perception and cortical activity we established here may prove useful as an efficient and easily accessible marker of altered cortical computation in neuropsychiatric disorders.

Neurological Events Following Transcatheter Aortic Valve Replacement and Their Predictors: A Report From the CoreValve Trials

BACKGROUND

The risk for stroke after transcatheter aortic valve replacement (TAVR) is an important concern. Identification of predictors for stroke is likely to be a critical factor aiding patient selection and management as TAVR use becomes widespread.

METHODS AND RESULTS

Patients enrolled in the CoreValve US Extreme Risk and High Risk Pivotal Trials or Continued Access Study treated with the self-expanding CoreValve bioprosthesis were included in this analysis. The 1-year stroke rate after TAVR was 8.4%. Analysis of the stroke hazard rate identified an early phase (0-10 days; 4.1% of strokes) and a late phase (11-365 days; 4.3% of strokes). Baseline predictors of early stroke included National Institutes of Health stroke scale score >0, prior stroke, prior transient ischemic attack, peripheral vascular disease, absence of prior coronary artery bypass surgery, angina, low body mass index (<21 kg/m(2)), and falls within the past 6 months. Significant procedural predictors were total time in the catheterization laboratory or operating room, delivery catheter in the body time, rapid pacing used during valvuloplasty, and repositioning of the prosthesis. Predictors of stroke between 11 and 365 days were small body surface area, severe aortic calcification, and falls within the past 6 months. There were no significant imaging predictors of early or late stroke.

CONCLUSIONS

Predictors of early stroke after TAVR included clinical and procedural factors; predictors of later stroke were limited to patient but not anatomic characteristics. These findings indicate that further refinement of imaging to identify anatomic factors predisposing to embolization may help improve stroke prediction in patients undergoing TAVR.

CLINICAL TRIAL REGISTRATIONS

URL: http://www.clinicaltrials.gov. Unique identifiers: NCT01240902, NCT01531374.

Action Planning and the Timescale of Evidence Accumulation

Perceptual decisions are based on the temporal integration of sensory evidence for different states of the outside world. The timescale of this integration process varies widely across behavioral contexts and individuals, and it is diagnostic for the underlying neural mechanisms. In many situations, the decision-maker knows the required mapping between perceptual evidence and motor response (henceforth termed “sensory-motor contingency”) before decision formation. Here, the integrated evidence can be directly translated into a motor plan and, indeed, neural signatures of the integration process are evident as build-up activity in premotor brain regions. In other situations, however, the sensory-motor contingencies are unknown at the time of decision formation. We used behavioral psychophysics and computational modeling to test if knowledge about sensory-motor contingencies affects the timescale of perceptual evidence integration. We asked human observers to perform the same motion discrimination task, with or without trial-to-trial variations of the mapping between perceptual choice and motor response. When the mapping varied, it was either instructed before or after the stimulus presentation. We quantified the timescale of evidence integration under these different sensory-motor mapping conditions by means of two approaches. First, we analyzed subjects’ discrimination threshold as a function of stimulus duration. Second, we fitted a dynamical decision-making model to subjects’ choice behavior. The results from both approaches indicated that observers (i) integrated motion information for several hundred ms, (ii) used a shorter than optimal integration timescale, and (iii) used the same integration timescale under all sensory-motor mappings. We conclude that the mechanisms limiting the timescale of perceptual decisions are largely independent from long-term learning (under fixed mapping) or rapid acquisition (under variable mapping) of sensory-motor contingencies. This conclusion has implications for neurophysiological and neuroimaging studies of perceptual decision-making.

2-Year Outcomes in Patients Undergoing Surgical or Self-Expanding Transcatheter Aortic Valve Replacement

BACKGROUND

The U.S. pivotal trial for the self-expanding valve found that among patients with severe aortic stenosis at increased risk for surgery, the 1-year survival rate was 4.9 percentage points higher in patients treated with a self-expanding transcatheter aortic valve bioprosthesis than in those treated with a surgical bioprosthesis.

OBJECTIVES

Longer-term clinical outcomes were examined to confirm if this mortality benefit is sustained.

METHODS

Patients with severe aortic stenosis who were at increased surgical risk were recruited. Eligible patients were randomly assigned in a 1:1 ratio to transcatheter aortic valve replacement with the self-expanding transcatheter valve (transcatheter aortic valve replacement [TAVR] group) or to aortic valve replacement with a surgical bioprosthesis (surgical group). The 2-year clinical and echocardiographic outcomes were evaluated in these patients.

RESULTS

A total of 797 patients underwent randomization at 45 centers in the United States. The rate of 2-year all-cause mortality was significantly lower in the TAVR group (22.2%) than in the surgical group (28.6%; log-rank test p < 0.05) in the as-treated cohort, with an absolute reduction in risk of 6.5 percentage points. Similar results were found in the intention-to-treat cohort (log-rank test p < 0.05). The rate of 2-year death or major stroke was significantly lower in the TAVR group (24.2%) than in the surgical group (32.5%; log-rank test p = 0.01).

CONCLUSIONS

In patients with severe aortic stenosis who are at increased surgical risk, the higher rate of survival with a self-expanding TAVR compared with surgery was sustained at 2 years. (Safety and Efficacy Study of the Medtronic CoreValve System in the Treatment of Symptomatic Severe Aortic Stenosis in High Risk and Very High Risk Subjects Who Need Aortic Valve Replacement; NCT01240902).

Analysis of mitral valve replacement outcomes is enhanced by meaningful clinical use of electronic health records

OBJECTIVE

Cardiac surgical mortality has improved during the last decade despite the aging of the population. An integrated US health plan developed a heart valve registry to track outcomes and complications of heart valve operations. This database was used for longitudinal evaluation of mitral valve (MV) outcomes from 1999 to 2008 at four affiliated hospitals.

METHODS

We identified 3130 patients in the Apollo database who underwent 3180 initial MV procedures. Internal administrative and Social Security Administration databases were merged to determine survival rates. Electronic health records were searched to ascertain demographics, comorbidities, and postoperative complications. Cox regression was used to evaluate mean survival and identify risk factors.

RESULTS

The procedures included 1160 mechanical valve replacements, 1159 tissue valve replacements, and 861 annuloplasties. The mean age of patients undergoing these procedures was 58 ± 11 years, 69 ± 12 years, and 62 ± 12 years, respectively. Mean survival was 8.9 ± 0.1 years for mechanical valve replacement, 7.0 ± 0.1 years for tissue valve replacement, and 7.7 ± 0.1 years for annuloplasty. Early in the study, there was a preference for implanting mechanical MVs. Beginning in 2003, more patients received tissue valve replacements rather than mechanical valves. Over time, there was an increasing trend of annuloplasty. Cox regression analysis identified the following risk factors for increased ten-year mortality: tissue valve implantation; advanced age; female sex; nonelective, nonisolated procedure; diabetes; postoperative use of banked blood products; previous cardiovascular intervention; dialysis; and longer perfusion time. Hospital location, reoperation, preoperative anticoagulation, and cardiogenic shock were not statistically significant risk factors.

CONCLUSIONS

When controlling for other risk factors, we observed a lower long-term survival rate for tissue valve replacement compared with mechanical valve replacement. Integrating electronic health records with existing electronic databases provided near-real-time analysis of longitudinal cardiac surgical outcomes.

The timescale of perceptual evidence integration can be adapted to the environment

A key computation underlying perceptual decisions is the temporal integration of "evidence" in favor of different states of the world. Studies from psychology and neuroscience have shown that observers integrate multiple samples of noisy perceptual evidence over time toward a decision. An influential model posits perfect evidence integration (i.e., without forgetting), enabling optimal decisions based on stationary evidence. However, in real-life environments, the perceptual evidence typically changes continuously. We used a computational model to show that, under such conditions, performance can be improved by means of leaky (forgetful) integration, if the integration timescale is adapted toward the predominant signal duration. We then tested whether human observers employ such an adaptive integration process. Observers had to detect visual luminance "signals" of variable strength, duration, and onset latency, embedded within longer streams of noise. Different sessions entailed predominantly short or long signals. The rate of performance improvement as a function of signal duration indicated that observers indeed changed their integration timescale with the predominant signal duration, in accordance with the adaptive integration account. Our findings establish that leaky integration of perceptual evidence is flexible and that cognitive control mechanisms can exploit this flexibility for optimizing the decision process.

Gastrointestinal complications associated with cardiopulmonary bypass procedures

Gastrointestinal complications after cardiopulmonary bypass (CPB) procedures are rare, but when they do occur, they carry a significant incidence of morbidity and mortality. Over a 5-year period spanning 1988-1992, 4923 CPB procedures were performed and 64 patients were identified who suffered a GI complication, giving an incidence of 1.3 per cent. The most frequent complications were GI bleeding (40%) and pancreatitis (34%). Other complications included acute cholecystitis (11%), perforated duodenal ulcer (8%), ischemic bowel (5%), and diverticulitis (2%). Complications occurred most frequently in patients undergoing procedures with longer pump and cross-clamp times, such as valvular and combination (CABG/valve) procedures. Redo procedures and the use of an intra-aortic balloon pump increased the risk of developing a GI complication 2.5 and 12 times, respectively. Patients were treated aggressively both medically and surgically, but suffered a higher mortality (16%) as compared to those not suffering a GI complication (3%). We conclude that GI complications after CPB procedures are infrequent but lethal. Clinical features are often subtle, and a high index of suspicion is needed for early diagnosis and aggressive treatment.

Glacier Surge Mechanism: 1982-1983 Surge of Variegated Glacier, Alaska

The hundredfold speedup in glacier motion in a surge of the kind the kind that took place in Variegated Glacier in 1982-1983 is caused by the buildup of high water pressure in the basal passageway system, which is made possible by a fundamental and pervasive change in the geometry and water-transport characteristics of this system. The behavior of the glacier in surge has many remarkable features, which can provide clues to a detailed theory of the surging process. The surge mechanism is akin to a proposed mechanism of overthrust faulting.