Cognitive loading affects motor awareness and movement kinematics but not locomotor trajectories during goal-directed walking in a virtual reality environment.

The primary purpose of this study was to investigate the effects of cognitive loading on movement kinematics and trajectory formation during goal-directed walking in a virtual reality (VR) environment. The secondary objective was to measure how participants corrected their trajectories for perturbed feedback and how participants' awareness of such perturbations changed under cognitive loading. We asked 14 healthy young adults to walk towards four different target locations in a VR environment while their movements were tracked and played back in real-time on a large projection screen. In 75% of all trials we introduced angular deviations of ±5° to ±30° between the veridical walking trajectory and the visual feedback. Participants performed a second experimental block under cognitive load (serial-7 subtraction, counter-balanced across participants). We measured walking kinematics (joint-angles, velocity profiles) and motor performance (end-point-compensation, trajectory-deviations). Motor awareness was determined by asking participants to rate the veracity of the feedback after every trial. In-line with previous findings in natural settings, participants displayed stereotypical walking trajectories in a VR environment. Our results extend these findings as they demonstrate that taxing cognitive resources did not affect trajectory formation and deviations although it interfered with the participants' movement kinematics, in particular walking velocity. Additionally, we report that motor awareness was selectively impaired by the secondary task in trials with high perceptual uncertainty. Compared with data on eye and arm movements our findings lend support to the hypothesis that the central nervous system (CNS) uses common mechanisms to govern goal-directed movements, including locomotion. We discuss our results with respect to the use of VR methods in gait control and rehabilitation

Altered visual feedback from an embodied avatar unconsciously influences movement amplitude and muscle activity

Evidence suggests that the sense of the position of our body parts can be surreptitiously deceived, for instance through illusory visual inputs. However, whether altered visual feedback during limb movement can induce substantial unconscious motor and muscular adjustments is not known. To address this question, we covertly manipulated virtual body movements in immersive virtual reality. Participants were instructed to flex their elbow to 90° while tensing an elastic band, as their virtual arm reproduced the same, a reduced (75°), or an amplified (105°) movement. We recorded muscle activity using electromyography, and assessed body ownership, agency and proprioception of the arm. Our results not only show that participants compensated for the avatar’s manipulated arm movement while being completely unaware of it, but also that it is possible to induce unconscious motor adaptations requiring significant changes in muscular activity. Altered visual feedback through body ownership illusions can influence motor performance in a process that bypasses awareness

Five-years surveillance of invasive aspergillosis in a university hospital

<p>Abstract</p> <p>Background</p> <p>As the most common invasive fungal infection, invasive aspergillosis (IA) remains a serious complication in immunocompromised patients, leading to increased mortality. Antifungal therapy is expensive and may result in severe adverse effects.</p> <p>The aim of this study was to determine the incidence of invasive aspergillosis (IA) cases in a tertiary care university hospital using a standardized surveillance method.</p> <p>Methods</p> <p>All inpatients at our facility were screened for presence of the following parameters: positive microbiological culture, pathologist's diagnosis and antifungal treatment as reported by the hospital pharmacy. Patients fulfilling one or more of these indicators were further reviewed and, if appropriate, classified according to international consensus criteria (EORTC).</p> <p>Results</p> <p>704 patients were positive for at least one of the indicators mentioned above. Applying the EORTC criteria, 214 IA cases were detected, of which 56 were proven, 25 probable and 133 possible. 44 of the 81 (54%) proven and probable cases were considered health-care associated. 37 of the proven/probable IA cases had received solid organ transplantation, an additional 8 had undergone stem cell transplantation, and 10 patients were suffering from some type of malignancy. All the other patients in this group were also suffering from severe organic diseases, required long treatment and experienced several clinical complications. 7 of the 56 proven cases would have been missed without autopsy. After the antimycotic prophylaxis regimen was altered, we noticed a significant decrease (p = 0.0004) of IA during the investigation period (2003-2007).</p> <p>Conclusion</p> <p>Solid organ and stem cell transplantation remain important risk factors for IA, but several other types of immunosuppression should also be kept in mind. Clinical diagnosis of IA may be difficult (in this study 13% of all proven cases were diagnosed by autopsy only). Thus, we confirm the importance of IA surveillance in all high-risk patients.</p

The sense of agency as tracking control

Does sense of agency (SoA) arise merely from action-outcome associations, or does an additional real-time process track each step along the chain? Tracking control predicts that deviant intermediate steps between action and outcome should reduce SoA. In two experiments, participants learned mappings between two finger actions and two tones. In later test blocks, actions triggered a robot hand moving either the same or a different finger, and also triggered tones, which were congruent or incongruent with the mapping. The perceived delay between actions and tones gave a proxy measure for SoA. Action-tone binding was stronger for congruent than incongruent tones, but only when the robot movement was also congruent. Congruent tones also had reduced N amplitudes, but again only when the robot movement was congruent.We suggest that SoA partly depends on a real time tracking control mechanism, since deviant intermediate action of the robot reduced SoA over the tone

How does it feel to act together?

This paper on the phenomenology of joint agency proposes a foray into a little explored territory at the intersection of two very active domains of research: joint action and sense of agency. I explore two ways in which our experience of joint agency may differ from our experience of individual agency. First, the mechanisms of action specification and control involved in joint action are typically more complex than those present in individual actions, since it is crucial for joint action that people coordinate their plans and actions. I discuss the implications that these coordination requirements might have for the strength of the sense of agency an agent may experience for a joint action. Second, engagement in joint action may involve a transformation of agentive identity and a partial or complete shift from a sense of self-agency to a sense of we-agency. I discuss several factors that may contribute to shaping our sense of agentive identity in joint action

Multisensory Stimulation Can Induce an Illusion of Larger Belly Size in Immersive Virtual Reality

Background: Body change illusions have been of great interest in recent years for the understanding of how the brain represents the body. Appropriate multisensory stimulation can induce an illusion of ownership over a rubber or virtual arm, simple types of out-of-the-body experiences, and even ownership with respect to an alternate whole body. Here we use immersive virtual reality to investigate whether the illusion of a dramatic increase in belly size can be induced in males through (a) first person perspective position (b) synchronous visual-motor correlation between real and virtual arm movements, and (c) self-induced synchronous visual-tactile stimulation in the stomach area.Methodology: Twenty two participants entered into a virtual reality (VR) delivered through a stereo head-tracked wide field-of-view head-mounted display. They saw from a first person perspective a virtual body substituting their own that had an inflated belly. For four minutes they repeatedly prodded their real belly with a rod that had a virtual counterpart that they saw in the VR. There was a synchronous condition where their prodding movements were synchronous with what they felt and saw and an asynchronous condition where this was not the case. The experiment was repeated twice for each participant in counter-balanced order. Responses were measured by questionnaire, and also a comparison of before and after self-estimates of belly size produced by direct visual manipulation of the virtual body seen from the first person perspective.Conclusions: The results show that first person perspective of a virtual body that substitutes for the own body in virtual reality, together with synchronous multisensory stimulation can temporarily produce changes in body representation towards the larger belly size. This was demonstrated by (a) questionnaire results, (b) the difference between the self-estimated belly size, judged from a first person perspective, after and before the experimental manipulation, and (c) significant positive correlations between these two measures. We discuss this result in the general context of body ownership illusions, and suggest applications including treatment for body size distortion illnesses

TMS stimulation over the inferior parietal cortex disrupts prospective sense of agency

Sense of agency refers to the feeling of controlling an external event through one's own action. On one influential view, sense of agency is inferred after an action, by "retrospectively" comparing actual effects of actions against their intended effects. However, it has been recently shown that earlier processes, linked to action selection, may also contribute to sense of agency, in advance of the action itself, and independently of action effects. The inferior parietal cortex (IPC) may underpin this "prospective" contribution to agency, by monitoring signals relating to fluency of action selection in dorsolateral prefrontal cortex (DLPFC). Here, we combined transcranial stimulation (TMS) with subliminal priming of action selection to investigate the causal role of these regions in the prospective coding of agency. In a first experiment, we showed that TMS over left IPC at the time of action selection disrupts perceived control over subsequent effects of action. In a second experiment, we exploited the temporal specificity of single-pulse TMS to pinpoint the exact timing of IPC contribution to sense of agency. We replicated the reduction in perceived control at the point of action selection, while observing no effect of TMS-induced disruption of IPC at the time of action outcomes

Approche neuroéconomique de la prise de risque à l’adolescence

International audienceRisk-taking behaviors represent the main cause of morbi-mortality in adolescence. Here, we analyze their neural correlates, based on a neuroeconomics approach. This approach postulates that risk-taking behaviors result from multiple decision-making biases that impair the selection of the most appropriate action among alternatives based on their subjective evaluation. Specifically, we investigate three important domains in value-based decision-making: risk aversion, loss aversion and intertemporal choice.Les comportements à risque représentent la principale source de morbimortalité à l’adolescence. Nous proposons ici une revue des apports de l’approche neuroéconomique à la compréhension des bases physiopathologiques des comportements à risque dans cette tranche d’âge. Les outils de la neuroéconomie suggèrent en effet que les conduites à risque résultent d’un certain nombre de biais affectant le processus de prise de décision des individus – processus guidant la sélection d’un comportement adapté parmi plusieurs alternatives en fonction de leur évaluation subjective. Il a ainsi été montré que les adolescents tendent à choisir les options les plus risquées car ils ressentiraient moins d’aversion au risque et à la perte que les adultes, et parce qu’ils dévalueraient de manière particulièrement importante les conséquences futures de leurs choix. Nous présentons également dans cette revue des résultats suggérant que la fréquence élevée des comportements à risque à l’adolescence peut être reliée aux processus de maturation de deux systèmes neuronaux majeurs : les régions cérébrales du système motivationnel et celles du cortex préfrontal

Analyse de la Connectivité Structurelle Cérébrale en Fonction du Quotient Intellectuel chez l’Adolescent

International audienc