Stimulus statistics shape oscillations in nonlinear recurrent neural networks.

Rhythmic activity plays a central role in neural computations and brain functions ranging from homeostasis to attention, as well as in neurological and neuropsychiatric disorders. Despite this pervasiveness, little is known about the mechanisms whereby the frequency and power of oscillatory activity are modulated, and how they reflect the inputs received by neurons. Numerous studies have reported input-dependent fluctuations in peak frequency and power (as well as couplings across these features). However, it remains unresolved what mediates these spectral shifts among neural populations. Extending previous findings regarding stochastic nonlinear systems and experimental observations, we provide analytical insights regarding oscillatory responses of neural populations to stimulation from either endogenous or exogenous origins. Using a deceptively simple yet sparse and randomly connected network of neurons, we show how spiking inputs can reliably modulate the peak frequency and power expressed by synchronous neural populations without any changes in circuitry. Our results reveal that a generic, non-nonlinear and input-induced mechanism can robustly mediate these spectral fluctuations, and thus provide a framework in which inputs to the neurons bidirectionally regulate both the frequency and power expressed by synchronous populations. Theoretical and computational analysis of the ensuing spectral fluctuations was found to reflect the underlying dynamics of the input stimuli driving the neurons. Our results provide insights regarding a generic mechanism supporting spectral transitions observed across cortical networks and spanning multiple frequency bands

What makes medical students better listeners?

Diagnosing heart conditions by auscultation is an important clinical skill commonly learnt by medical students. Clinical proficiency for this skill is in decline [1], and new teaching methods are needed. Successful discrimination of heartbeat sounds is believed to benefit mainly from acoustical training [2]. From recent studies of auditory training [3,4] we hypothesized that semantic representations outside the auditory cortex contribute to diagnostic accuracy in cardiac auscultation. To test this hypothesis, we analysed auditory evoked potentials (AEPs) which were recorded from medical students while they diagnosed quadruplets of heartbeat cycles. The comparison of trials with correct (Hits) versus incorrect diagnosis (Misses) revealed a significant difference in brain activity at 280-310 ms after the onset of the second cycle within the left middle frontal gyrus (MFG) and the right prefrontal cortex. This timing and locus suggest that semantic rather than acoustic representations contribute critically to auscultation skills. Thus, teaching auscultation should emphasize the link between the heartbeat sound and its meaning. Beyond cardiac auscultation, this issue is of interest for all fields where subtle but complex perceptual differences identify items in a well-known semantic context

MDCT-findings in patients with non-occlusive mesenteric ischemia (NOMI): influence of vasoconstrictor agents.

To evaluate the influence of vasoconstrictor agents (VCAs) on signs of vasoconstriction and bowel ischemia on MDCT detected in patients with non-occlusive mesenteric ischemia (NOMI). This 8-year single-center retrospective study consecutively included all patients with histopathologically proven NOMI who underwent MDCT ≤ 48 h prior to surgical bowel resection. Two blinded radiologists jointly reviewed each examination for signs of bowel ischemia, abdominal organ infarct, mesenteric vessel size and regularity, and ancillary vascular findings. VCA administration (length and dosage), clinical and biochemical data, risk factors, and outcomes were retrieved from patients' medical records. Subgroup comparisons were performed. Ninety patients were included (59 males, mean age 65 years); 40 (44.4%) had received VCAs before MDCT. Overall mortality was 32% (n = 29), with no significant difference between the two groups. In patients treated with VCAs, the calibre of the superior mesenteric artery (SMA) was smaller (p = 0.032), and vasoconstriction of its branches tended to be more important (p = 0.096) than in patients not treated with VCAs. The presence and extent of bowel ischemia did not significantly correlate with VCA administration, but abdominal organ infarcts tended to be more frequent (p = 0.005) and involved more organs (p = 0.088). The VCA group had lower mean arterial pressure (p = 0.006) and lower hemoglobin levels (p < 0.001). Several biomarkers of organ failure and inflammation, differed significantly with VCA use, proving worse clinical condition. MDCT demonstrates more severe SMA vasoconstriction and tends to show increased abdominal organ infarcts after VCA administration in NOMI patients compared to NOMI patients not treated with VCAs. • In critically ill patients with NOMI, MDCT demonstrates VCA support via increased vasoconstriction of the main SMA and its branches. • VCA administration in NOMI patients tends to contribute to the development of organ infarcts, as shown on MDCT. • An important degree of vasoconstriction in NOMI patients may indicate insufficient resuscitation and, thus, help clinicians in further patient management

Representation of Sound Objects within Early-Stage Auditory Areas: A Repetition Effect Study Using 7T fMRI.

Environmental sounds are highly complex stimuli whose recognition depends on the interaction of top-down and bottom-up processes in the brain. Their semantic representations were shown to yield repetition suppression effects, i. e. a decrease in activity during exposure to a sound that is perceived as belonging to the same source as a preceding sound. Making use of the high spatial resolution of 7T fMRI we have investigated the representations of sound objects within early-stage auditory areas on the supratemporal plane. The primary auditory cortex was identified by means of tonotopic mapping and the non-primary areas by comparison with previous histological studies. Repeated presentations of different exemplars of the same sound source, as compared to the presentation of different sound sources, yielded significant repetition suppression effects within a subset of early-stage areas. This effect was found within the right hemisphere in primary areas A1 and R as well as two non-primary areas on the antero-medial part of the planum temporale, and within the left hemisphere in A1 and a non-primary area on the medial part of Heschl's gyrus. Thus, several, but not all early-stage auditory areas encode the meaning of environmental sounds

Emotional pre-eminence of human vocalizations.

Human vocalizations (HV), as well as environmental sounds, convey a wide range of information, including emotional expressions. The latter have been relatively rarely investigated, and, in particular, it is unclear if duration-controlled non-linguistic HV sequences can reliably convey both positive and negative emotional information. The aims of the present psychophysical study were: (i) to generate a battery of duration-controlled and acoustically controlled extreme valence stimuli, and (ii) to compare the emotional impact of HV with that of other environmental sounds. A set of 144 HV and other environmental sounds was selected to cover emotionally positive, negative, and neutral values. Sequences of 2 s duration were rated on Likert scales by 16 listeners along three emotional dimensions (arousal, intensity, and valence) and two non-emotional dimensions (confidence in identifying the sound source and perceived loudness). The 2 s stimuli were reliably perceived as emotionally positive, negative or neutral. We observed a linear relationship between intensity and arousal ratings and a "boomerang-shaped" intensity-valence distribution, as previously reported for longer, duration-variable stimuli. In addition, the emotional intensity ratings for HV were higher than for other environmental sounds, suggesting that HV constitute a characteristic class of emotional auditory stimuli. In addition, emotionally positive HV were more readily identified than other sounds, and emotionally negative stimuli, irrespective of their source, were perceived as louder than their positive and neutral counterparts. In conclusion, HV are a distinct emotional category of environmental sounds and they retain this emotional pre-eminence even when presented for brief periods

Brain mechanisms for perceiving illusory lines in humans.

Illusory contours (ICs) are perceptions of visual borders despite absent contrast gradients. The psychophysical and neurobiological mechanisms of IC processes have been studied across species and diverse brain imaging/mapping techniques. Nonetheless, debate continues regarding whether IC sensitivity results from a (presumably) feedforward process within low-level visual cortices (V1/V2) or instead are processed first within higher-order brain regions, such as lateral occipital cortices (LOC). Studies in animal models, which generally favour a feedforward mechanism within V1/V2, have typically involved stimuli inducing IC lines. By contrast, studies in humans generally favour a mechanism where IC sensitivity is mediated by LOC and have typically involved stimuli inducing IC forms or shapes. Thus, the particular stimulus features used may strongly contribute to the model of IC sensitivity supported. To address this, we recorded visual evoked potentials (VEPs) while presenting human observers with an array of 10 inducers within the central 5°, two of which could be oriented to induce an IC line on a given trial. VEPs were analysed using an electrical neuroimaging framework. Sensitivity to the presence vs. absence of centrally-presented IC lines was first apparent at ∼200 ms post-stimulus onset and was evident as topographic differences across conditions. We also localized these differences to the LOC. The timing and localization of these effects are consistent with a model of IC sensitivity commencing within higher-level visual cortices. We propose that prior observations of effects within lower-tier cortices (V1/V2) are the result of feedback from IC sensitivity that originates instead within higher-tier cortices (LOC)

Necrotizing pneumonia in children: Chest computed tomography vs. lung ultrasound.

The utilization of contrast-enhanced computed tomography (CT) of the chest for the diagnosis of necrotizing pneumonia (NP), a complication of community-acquired pneumonia, is controversial because of the inherent ionizing radiation involved. Over the past few years, the growing availability of bedside Lung Ultrasound (LUS) devices has led to increased use of this nonionizing imaging method for diagnosing thoracic pathology, including pneumonia. The objectives of this study were as follows: first, to compare the performance of LUS vs. CT in the identification of certain radiological signs of NP, and second, to determine whether LUS could replace CT in the diagnosis of NP. We compared retrospectively the CT and LUS images of 41 patients between 2005 and 2018 in whom at least one contrast-injected chest CT scan and one LUS had been undertaken fewer than 7 days apart. Pleural effusions were demonstrated almost systematically (100% on CT vs. 95.8% on LUS). Visualization of septations in pleural effusions was clearly superior on LUS (20.4% on CT vs 62.5% on LUS). Concerning the detection of necrosis, we observed a strong correlation between LUS and the gold-standard CT (95.8% on LUS vs. 93.7% on CT). Parenchymal cavities were more easily detected on CT than on LUS (79.1 vs. 35.4%). LUS has shown to be as effective as CT in the diagnosis of NP. The use of CT in patients with NP could be limited to the detection of complications such as bronchopleural fistulae in unfavorably evolving diseases

Effects of various generations of iterative CT reconstruction algorithms on low-contrast detectability as a function of the effective abdominal diameter: A quantitative task-based phantom study.

To investigate how various generations of iterative reconstruction (IR) algorithms impact low-contrast detectability (LCD) in abdominal computed tomography (CT) for different patient effective diameters, using a quantitative task-based approach. Investigations were performed using an anthropomorphic abdominal phantom with two optional additional rings to simulate varying patient effective diameters (25, 30, and 35 cm), and containing multiple spherical targets (5, 6, and 8 mm in diameter) with a 20-HU contrast difference. The phantom was scanned using routine abdominal protocols (CTDI <sub>vol</sub> , 5.9-16 mGy) on four CT systems from two manufacturers. Images were reconstructed using both filtered back-projection (FBP) and various IR algorithms: ASiR 50%, SAFIRE 3 (both statistical IRs), ASiR-V 50%, ADMIRE 3 (both partial model-based IRs), or Veo (full model-based IR). Section thickness/interval was 2/1 mm or 2.5/1.25 mm, except 0.625/0.625 mm for Veo. We assessed LCD using a channelized Hotelling observer with 10 dense differences of Gaussian channels, with the area under the receiver operating characteristic curve (AUC) as a figure of merit. For the smallest phantom (25-cm diameter) and smallest lesion size (5-mm diameter), AUC for FBP and the various IR algorithms did not significantly differ for any of the tested CT systems. For the largest phantom (35-cm diameter), Veo yielded the highest AUC improvement (8.5%). Statistical and partial model-based IR algorithms did not significantly improve LCD. In abdominal CT, switching from FBP to IR algorithms offers limited possibilities for achieving significant dose reductions while ensuring a constant objective LCD

Iterative Reconstructions in Reduced-Dose CT: Which Type Ensures Diagnostic Image Quality in Young Oncology Patients?

To compare adaptive statistical iterative reconstruction (ASIR) and model-based iterative reconstruction (MBIR) algorithms for reduced-dose computed tomography (CT). Forty-four young oncology patients (mean age 30 ± 9 years) were included. After routine thoraco-abdominal CT (dose 100%, average CTDI javax.xml.bind.JAXBElement@e7f585f 9.1 ± 2.4 mGy, range 4.4-16.9 mGy), follow-up CT was acquired at 50% (average CTDI javax.xml.bind.JAXBElement@2e35610f 4.5 ± 1.2 mGy, range 2.2-8.4 mGy) in 29 patients additionally at 20% dose (average CTDI javax.xml.bind.JAXBElement@37ad3473 1.9 ± 0.5 mGy, range 0.9-3.4 mGy). Each reduced-dose CT was reconstructed using both ASIR and MBIR. Four radiologists (two juniors and two seniors) blinded to dose and technique read each set of CT images regarding objective and subjective image qualities (high- or low-contrast structures), subjective noise or pixilated appearance, diagnostic confidence, and lesion detection. At all dose levels, objective image noise was significantly lower with MBIR than with ASIR (P < 0.001). The subjective image quality for low-contrast structures was significantly higher with MBIR than with ASIR (P < 0.001). Reduced-dose abdominal CT images of patients with higher body mass index (BMI) were read with significantly higher diagnostic confidence than images of slimmer patients (P < 0.001) and had higher subjective image quality, regardless of technique. Although MBIR images appeared significantly more pixilated than ASIR images, they were read with higher diagnostic confidence, especially by juniors (P < 0.001). Reduced-dose CT during the follow-up of young oncology patients should be reconstructed with MBIR to ensure diagnostic quality. Elevated body mass index does not hamper the quality of reduced-dose CT

Alcoholic liver disease confers a worse prognosis than HCV infection and non-alcoholic fatty liver disease among patients with cirrhosis: An observational study.

Cirrhosis is a heterogeneous clinical condition that includes patients at wide-ranging stages of severity. The role of the underlying liver disease on patient prognosis remains unclear. To assess the impact of the underlying liver disease on the occurrence of hepatocellular carcinoma (HCC) and death. Data related to the occurrence of HCC and death were collected during a 21-year period among patients with cirrhosis related to alcoholic liver disease (ALD) (n = 529), chronic hepatitis C virus (HCV) infection (n = 145) or non-alcoholic fatty liver disease (NAFLD) (n = 78). At inclusion, ALD patients were younger than HCV and NAFLD patients (56 vs. 67 vs. 63 years; p<0.001) and had worse liver function (percent of patients with Child-Pugh stages B or C: 48% vs. 8% vs. 17%; p<0.001). During follow-up, 85 patients developed HCC and 379 died. The 10-year cumulative incidence rate of HCC was lower in ALD patients than in HCV and NAFLD patients (8.4% vs. 22.0% vs. 23.7%; p<0.001). The 10-year cumulative incidence rates of mortality were not statistically different between ALD, HCV and NAFLD patients (58.1% vs. 47.7% vs. 49.9%; p = 0.078). Alcohol abstinence and viral eradication were associated with reduced mortality among ALD and HCV patients, respectively. In multivariate analyses, ALD was associated with a reduced risk of HCC (0.39; 95% CI, 0.20-0.76; p = 0.005) but with a higher risk of mortality (1.53; 95% CI, 1.20-1.95; p<0.001). ALD patients died more frequently from decompensation of cirrhosis. Despite a lower incidence of HCC, patients with ALD-related cirrhosis have a worse outcome than those with chronic HCV infection or NAFLD-related cirrhosis