Rehabilitation of working memory after acquired brain injury and multiple sclerosis: A systematic review.

The objective is to study the effectiveness of working memory (WM) rehabilitation after Acquired brain injury (ABI) and multiple sclerosis (MS). A systematic database search of published studies, following PRISMA recommendations, with assessment of methodological quality and risk of bias, was conducted. The results were analysed according to the rehabilitation method used. 31 studies (including 14 class I) were included, and 11 different training programs were identified. Despite great variability in training methodology and outcome measures, the results were positive overall. However, only three rehabilitation programs showed a transfer effect to WM (near) and daily life with long-term maintenance. The results were more variable for protocols limited to the use of computerized n-back training tasks. Overall, the current evidence supports multi-task WM training rather than single-task-limited program. It also supports early and long duration training, with some therapist support. However, it is not possible, to date, to make strong recommendations regarding the rehabilitation program to be used preferentially. Although results are encouraging, level of evidence remains modest, particularly regarding the maintenance of the therapeutic effect after the end of training, and the transfer to everyday life skills. The influence of rehabilitation parameters (training duration, therapist involvement … ) remains difficult to assess.

The stochastic edge in adaptive evolution.

In a recent article, Desai and Fisher proposed that the speed of adaptation in an asexual population is determined by the dynamics of the stochastic edge of the population, that is, by the emergence and subsequent establishment of rare mutants that exceed the fitness of all sequences currently present in the population. Desai and Fisher perform an elaborate stochastic calculation of the mean time tau until a new class of mutants has been established and interpret 1/tau as the speed of adaptation. As they note, however, their calculations are valid only for moderate speeds. This limitation arises from their method to determine tau: Desai and Fisher back extrapolate the value of tau from the best-fit class's exponential growth at infinite time. This approach is not valid when the population adapts rapidly, because in this case the best-fit class grows nonexponentially during the relevant time interval. Here, we substantially extend Desai and Fisher's analysis of the stochastic edge. We show that we can apply Desai and Fisher's method to high speeds by either exponentially back extrapolating from finite time or using a nonexponential back extrapolation. Our results are compatible with predictions made using a different analytical approach (Rouzine et al.) and agree well with numerical simulations.

The traveling-wave approach to asexual evolution: Muller's ratchet and speed of adaptation.

We use traveling-wave theory to derive expressions for the rate of accumulation of deleterious mutations under Muller's ratchet and the speed of adaptation under positive selection in asexual populations. Traveling-wave theory is a semi-deterministic description of an evolving population, where the bulk of the population is modeled using deterministic equations, but the class of the highest-fitness genotypes, whose evolution over time determines loss or gain of fitness in the population, is given proper stochastic treatment. We derive improved methods to model the highest-fitness class (the stochastic edge) for both Muller's ratchet and adaptive evolution, and calculate analytic correction terms that compensate for inaccuracies which arise when treating discrete fitness classes as a continuum. We show that traveling-wave theory makes excellent predictions for the rate of mutation accumulation in the case of Muller's ratchet, and makes good predictions for the speed of adaptation in a very broad parameter range. We predict the adaptation rate to grow logarithmically in the population size until the population size is extremely large.

Universal tree structures in directed polymers and models of evolving populations.

By measuring or calculating coalescence times for several models of coalescence or evolution, with and without selection, we show that the ratios of these coalescence times become universal in the large size limit and we identify a few universality classes.

Empathy examined through the neural mechanisms involved in imagining how I feel versus how you feel pain.

Perspective-taking is a stepping stone to human empathy. When empathizing with another individual, one can imagine how the other perceives the situation and feels as a result. To what extent does imagining the other differs from imagining oneself in similar painful situations? In this functional magnetic resonance imaging experiment, participants were shown pictures of people with their hands or feet in painful or non-painful situations and instructed to imagine and rate the level of pain perceived from different perspectives. Both the Self's and the Other's perspectives were associated with activation in the neural network involved in pain processing, including the parietal operculum, anterior cingulate cortex (ACC; BA32) and anterior insula. However, the Self-perspective yielded higher pain ratings and involved the pain matrix more extensively in the secondary somatosensory cortex, the ACC (BA 24a'/24b'), and the insula proper. Adopting the perspective of the Other was associated with specific increase in the posterior cingulate/precuneus and the right temporo-parietal junction. These results show the similarities between Self- and Other-pain representation, but most interestingly they also highlight some distinctiveness between these two representations, which is a crucial aspect of human empathy. It may be what allows us to distinguish empathic responses to others versus our own personal distress. These findings are consistent with the view that empathy does not involve a complete Self-Other merging.

Exactly soluble noisy traveling-wave equation appearing in the problem of directed polymers in a random medium.

We calculate exactly the velocity and diffusion constant of a microscopic stochastic model of N evolving particles which can be described by a noisy traveling-wave equation with a noise of order N(-1/2). Our model can be viewed as the infinite range limit of a directed polymer in random medium with N sites in the transverse direction. Despite some peculiarities of the traveling-wave equations in the absence of noise, our exact solution allows us to test the validity of a simple cutoff approximation and to show that, in the weak noise limit, the position of the front can be completely described by the effect of the noise on the first particle.

Fluctuations of the winding number of a directed polymer in a random medium.

For a directed polymer in a random medium lying on an infinite cylinder that is in 1+1 dimensions with finite width and periodic boundary conditions on the transverse direction, the winding number is simply the algebraic number of turns the polymer does around the cylinder. This paper presents exact expressions of the fluctuations of this winding number due to, first, the thermal noise of the system and, second, the different realizations of the disorder in the medium.

Abnormalities of brain function during a nonverbal theory of mind task in schizophrenia.

Theory of mind (ToM), the specific ability to attribute thoughts and feelings to oneself and others is generally impaired in schizophrenia. Previous studies demonstrated a deficit of the attribution of intentions to others among patients having formal thought disorder. During nonverbal tasks, such a function requires both the visual perception of human figures and the understanding of their intentions. These processes are considered to involve the superior temporal sulcus and the medial prefrontal cortex, respectively. Are the functional patterns of activation associated with those processes abnormal in schizophrenia? Seven schizophrenic patients on medication performed a nonverbal attribution of intentions task as well as two matched physical logic tasks, with and without human figures, while H2O15 PET-scanning was performed. Data from the patients were compared to those of eight healthy controls matched for verbal IQ and sex. The experimental design allowed dissociating the effect of the perception of human figures from that of the attribution of intentions. During attribution of intentions, significant activations in the right prefrontal cortex were detected in the control subjects. Those activations were not found in the schizophrenic group. However, in both groups, the perception of human figure elicited bilateral activation of the occipitotemporal regions and of the posterior part of the superior temporal sulcus. Schizophrenic patients performing a nonverbal attribution of intentions task have an abnormal cerebral activity.

Reasoning about physical causality and other's intentions in schizophrenia.

INTRODUCTION: Several studies have shown that schizophrenic patients have impaired theory-of-mind skills involving the attribution of false beliefs and intentions to others. Despite the methodological difficulties of false belief protocols, experiments have concluded that the deficit is specific and cannot be explained in terms of a general cognitive impairment. The situation, however, remains unclear as far as the attribution of intentions to others is concerned. We propose the use of nonverbal control tasks based on physical causality to demonstrate the specificity of the impairment of attribution of intentions. METHODS: We compared the performances of schizophrenic patients and normal subjects on the attribution of intentions and on two control tasks involving physical causality (reasoning about the weight, location, speed, and the physical properties of objects). 25 schizophrenic patients and 25 healthy subjects participated in the study. Each subject was assessed under three conditions using comic strips: attribution of intentions, physical causality with characters, physical causality without characters. RESULTS: The performances of schizophrenic patients differed significantly from those of healthy subjects only in the attribution of intentions condition. This difference was also found when only subjects having optimal performances in physical logic were considered and when verbal IQ was considered as a co-variable. CONCLUSIONS: Nonverbal attribution of intentions to others is specifically impaired in schizophrenia. This conclusion is in agreement with recent neuroimaging findings.