Dissociable contribution of the parietal and frontal cortex to coding movement direction and amplitude

© 2015 Davare, Zénon, Desmurget and Olivier. To reach for an object, we must convert its spatial location into an appropriate motor command, merging movement direction and amplitude. In humans, it has been suggested that this visuo-motor transformation occurs in a dorsomedial parieto-frontal pathway, although the causal contribution of the areas constituting the “reaching circuit” remains unknown. Here we used transcranial magnetic stimulation (TMS) in healthy volunteers to disrupt the function of either the medial intraparietal area (mIPS) or dorsal premotor cortex (PMd), in each hemisphere. The task consisted in performing step-tracking movements with the right wrist towards targets located in different directions and eccentricities; targets were either visible for the whole trial (Target-ON) or flashed for 200 ms (Target-OFF). Left and right mIPS disruption led to errors in the initial direction of movements performed towards contralateral targets. These errors were corrected online in the Target-ON condition but when the target was flashed for 200 ms, mIPS TMS manifested as a larger endpoint spreading. In contrast, left PMd virtual lesions led to higher acceleration and velocity peaks—two parameters typically used to probe the planned movement amplitude—irrespective of the target position, hemifield and presentation condition; in the Target-OFF condition, left PMd TMS induced overshooting and increased the endpoint dispersion along the axis of the target direction. These results indicate that left PMd intervenes in coding amplitude during movement preparation. The critical TMS timings leading to errors in direction and amplitude were different, namely 160–100 ms before movement onset for mIPS and 100–40 ms for left PMd. TMS applied over right PMd had no significant effect. These results demonstrate that, during motor preparation, direction and amplitude of goal-directed movements are processed by different cortical areas, at distinct timings, and according to a specific hemispheric organization.ARC (Actions de Recherche Concertées, Communauté Française de Belgique); Fondation Médicale Reine Elisabeth (FMRE) and from the Fonds de la Recherche Scientifique (FNRS–FDP); BBSRC David Phillips fellowship (UK), the Royal Society (UK); FWO Odysseus project (Fonds WetenschappelijkOnderzoek,Belgium).AZisaSeniorResearch AssociatesupportedbyINNOVIRIS

Effects of caffeine on neuromuscular fatigue and performance during high-intensity cycling exercise in moderate hypoxia

Purpose: To investigate the effects of caffeine on performance, neuromuscular fatigue and perception of effort during high-intensity cycling exercise in moderate hypoxia. Methods: Seven adult male participants firstly underwent an incremental exercise test on a cycle ergometer in conditions of acute normobaric hypoxia (fraction inspired oxygen = 0.15) to establish peak power output (PPO). In the following two visits, they performed a time to exhaustion test (78 ± 3% PPO) in the same hypoxic conditions after caffeine ingestion (4 mg kg$^{−1}$) and one after placebo ingestion in a double-blind, randomized, counterbalanced cross-over design. Results: Caffeine significantly improved time to exhaustion by 12%. A significant decrease in subjective fatigue was found after caffeine consumption. Perception of effort and surface electromyographic signal amplitude of the vastus lateralis were lower and heart rate was higher in the caffeine condition when compared to placebo. However, caffeine did not reduce the peripheral and central fatigue induced by high-intensity cycling exercise in moderate hypoxia. Conclusion: The caffeine-induced improvement in time to exhaustion during high-intensity cycling exercise in moderate hypoxia seems to be mediated by a reduction in perception of effort, which occurs despite no reduction in neuromuscular fatigue

Bilateral extracephalic transcranial direct current stimulation improves endurance performance in healthy individuals

Background: Transcranial direct current stimulation (tDCS) has been used to enhance endurance performance but its precise mechanisms and effects remain unknown. Objective: To investigate the effect of bilateral tDCS on neuromuscular function and performance during a cycling time to task failure (TTF) test. Methods: Twelve participants in randomized order received a placebo tDCS (SHAM) or real tDCS with two cathodes (CATHODAL) or two anodes (ANODAL) over bilateral motor cortices and the opposite electrode pair over the ipsilateral shoulders. Each session lasted 10 min and current was set at 2mA. Neuromuscular assessment was performed before and after tDCS and was followed by a cycling time to task failure (TTF) test. Heart rate (HR), ratings of perceived exertion (RPE), leg muscle pain (PAIN) and blood lactate accumulation (?B[La-]) in response to the cycling TTF test were measured. Results: Corticospinal excitability increased in the ANODAL condition (P < 0.001) while none of the other neuromuscular parameters showed any change. Neuromuscular parameters did not change in the SHAM and CATHODAL conditions. TTF was significantly longer in the ANODAL (P = 0.003) compared to CATHODAL and SHAM conditions (12.61 ± 4.65 min; 10.61 ± 4.34 min; 10.21 ± 3.47 min respectively), with significantly lower RPE and higher ?B[La-] (P < 0.001). No differences between conditions were found for HR (P = 0.803) and PAIN during the cycling TTF test (P = 0.305). Conclusion: Our findings demonstrate that tDCS with the anode over both motor cortices using a bilateral extracephalic reference improves endurance performance

Active sensing with artificial neural networks

The fitness of behaving agents depends on their knowledge of the environment, which demands efficient exploration strategies. Active sensing formalizes exploration as reduction of uncertainty about the current state of the environment. Despite strong theoretical justifications, active sensing has had limited applicability due to difficulty in estimating information gain. Here we address this issue by proposing a linear approximation to information gain and by implementing efficient gradient-based action selection within an artificial neural network setting. We compare information gain estimation with state of the art, and validate our model on an active sensing task based on MNIST dataset. We also propose an approximation that exploits the amortized inference network, and performs equally well in certain contexts

The cost of cognitive activity in a predictive coding framework

Cognitive activity is effortful and we tend to avoid cognitively demanding tasks. Despite the profound socioeconomic implication, we still don’t understand the origin of this subjective cost. We propose that cognitive effort can be formalized in the framework of predictive coding. This influential theory posits that the brain develops a hierarchical model of the world and that percepts and actions are shaped by continuous predictions of the incoming sensory information. Hence, in order to maintain our predictions accurate, we have to dynamically update our internal models. Here, we propose that such model updating incurs a certain cost, which, in turn, determines our perception of cognitive effort. We designed a novel category learning task in order to dissect the link between various aspects of model updating on the one hand, and task aversion and effort perception on the other hand. We used standard questionnaires and pupil size recording to evaluate subjective effort. We also used Hierarchical Gaussian Filters to model the evolution of subjects’ beliefs about stimulus category and hence, infer internal model updating. Our preliminary results (N=28) show that effort estimates were considerably higher for high category overlap as compared to low overlap. Given that high category overlap condition was also characterized by increased model updating, these early findings seem to be in accordance with our initial hypothesis

Predictive coding through the lens of the pupil

Pupil size responds to a plethora of cognitive processes and is known to be a reliable marker of arousal. Accordingly, pupil size increases in response to surprising or salient events. However, it remains unclear whether these pupil dilations correspond to responses to centralized, behaviorally relevant events or to prediction errors (PE; i.e. the difference between expected and actual stimulus) distributed across the brain, in accordance with Predictive Coding frameworks. Here, we ran 2 series of experiments in order to tease these hypotheses apart. In the first series, we tested 1) how pupil responds to non-frequent statistical regularities (transitions between stimuli), 2) how attention modulates these responses and 3) the relation between these responses and the level of awareness of the transition statistics. We show that pupil responds to rare transitions even when unconscious, suggesting that relevant events do not need to reach consciousness to trigger pupillary responses. In the second series of experiments we tested whether the pupil responds to perceptual PE (i.e. the temporal or spatial predictability of a stimulus), by showing participants full-screen kinematograms with low or high levels of predictability. Our preliminary results suggest that pupil does not respond to perceptual PE per se. Ongoing experiments are investigating whether, rather than absolute PE, pupil size could be viewed as a marker of precision-weighted PE, which depends crucially on context

Cognitive task avoidance correlates with fatigue-induced performance decrement but not with subjective fatigue

Mentally demanding tasks feel effortful and are usually avoided. Furthermore, prolonged cognitive engagement leads to mental fatigue, consisting of subjective feeling of exhaustion and decline in performance. Despite the intuitive characterization of fatigue as an increase in subjective effort perception, the effect of fatigue on effort cost has never been tested experimentally. To this end, sixty participants in 2 separate experiments underwent a forced-choice working memory task following either a fatigue-inducing (i.e. cognitive task involving working memory, conflict and switch costs) or a control manipulation. We measured fatigue in terms of subjective feeling and performance decrement and assessed effort in terms of subjective perception and task avoidance. Subjects exhibited only weak avoidance of the working memory task, with stronger influence of reward than task difficulty on their decisions. In addition, we found that task avoidance did not systematically change following the fatigue manipulation but that variations in task avoidance correlated with fatigue-induced performance decline. The other measures of fatigue and effort were unrelated to each other. Our findings suggest that subjective fatigue may develop independently of task avoidance and suggest an "anticipatory regulation" model in which fatigue urges subjects to stop in anticipation of possible, future adverse consequences

ANÁLISE DA INFLUÊNCIA DA SUPERFÍCIE LIVRE DO FLUIDO NAS VIBRAÇÕES LIVRES NÃO LINEARES DA CASCA CILÍNDRICA

Serão analisadas neste trabalho as vibrações não lineares de cascas cilíndricas simplesmente apoiadas, parcialmente, ou completamente, preenchidas por um fluído incompreessível, irrotacional e não viscoso, considerando a influência da superfície livre no comportamento não linear do sistema. Utiliza-se a teoria não linear de Donnell e de Sanders para cascas abatidas para a representação do campo de deformação e das mudanças de curvatura da casca cilíndrica, enquanto que a fluído é dado por um potencial de velocidade, que atende a equação de Laplace e as condições de contorno do problema. Considera-se um modelo de baixa dimensão, para descrever as soluções do campo de deslocamentos da casca, obtido a partir do método da perturbação que prescreve os principais modos não lineares que se acoplam ao modo linear de vibração da casca cilíndrica. A partir da função de Lagrange da casca cilíndrica e da equação da superfície livre do fluido e empregando o método de Rayleigh-Ritz, encontram-se as equações não lineares de movimento da casca cilíndrica. Investigam-se a presença da superfície livre do fluido e da geometria da casca no comportamento das vibrações livres não lineares

Hoehere Veredlung von Schweinshaut

Ziel des Forschungsvorhabens war die Sicherung des Know-how der mittel-staendischen Schweinslederbetriebe in Deutschland. Die Untersuchungen zur substratabhaengigen Nasszurichtung dienten dem Ziel, die Nasszurichtung beherrschbarer zu machen. Zur Loesung der Aufgabe wurde die Wasseraufnahme der gefalzten Leder zur Charakterisierung ihrer Wechselwirkung mit den Flotten der Nasszurichtung herangezogen. Der zweite Komplex diente der Verbesserung der Farbegalitaet und-echtheit sowie der Weichheit der Leder durch Enzyme in der Nasszurichtung. Die Untersuchungen zur thermischen Strukturbeeinflussung dienten dem Ziel, durch thermische Effekte die Schweinslederqualitaet zu verbessern. Die thermische Behandlung der Schweinshaeute wirkte hautaufschliessend und strukturverbesserndSIGLEAvailable from TU Bergakademie, Freiberg (DE)-FILK gGmbH, under shelf-number:9341 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Wirtschaft BMWi, Bonn (Germany); Projekttraeger Arbeitsgemeinschaft industrieller Forschungsvereinigungen Otto von Guericke e.V. AiF, Bonn, Berlin (Germany)DEGerman