Willingness towards cognitive engagement: a preliminary study based on a behavioural entropy approach

Faced with a novel task some people enthusiastically embark in it and work with determination, while others soon lose interest and progressively reduce their efforts. Although cognitive neuroscience has explored the behavioural and neural features of apathy, the why’s and how’s of positive engagement are only starting to be understood. Stemming from the observation that the left hemisphere is commonly associated to a proactive (‘do something’) disposition, we run a preliminary study exploring the possibility that individual variability in eagerness to engage in cognitive tasks could reflect a preferred left- or right-hemisphere functioning mode. We adapted a task based on response-independent reinforcement and used entropy to characterize the degree of involvement, diversification, and predictability of responses. Entropy was higher in women, who were overall more active, less dependent on instructions, and never reduced their engagement during the task. Conversely, men showed lower entropy, took longer pauses, and became significantly less active by the end of the allotted time, renewing their efforts mainly in response to negative incentives. These findings are discussed in the light of neurobiological data on gender differences in behaviour

Willingness towards cognitive engagement: a preliminary study based on a behavioural entropy approach

Faced with a novel task some people enthusiastically embark in it and work with determination, while others soon lose interest and progressively reduce their efforts. Although cognitive neuroscience has explored the behavioural and neural features of apathy, the why’s and how’s of positive engagement are only starting to be understood. Stemming from the observation that the left hemisphere is commonly associated to a proactive (‘do something’) disposition, we run a preliminary study exploring the possibility that individual variability in eagerness to engage in cognitive tasks could reflect a preferred left- or right-hemisphere functioning mode. We adapted a task based on response-independent reinforcement and used entropy to characterize the degree of involvement, diversification, and predictability of responses. Entropy was higher in women, who were overall more active, less dependent on instructions, and never reduced their engagement during the task. Conversely, men showed lower entropy, took longer pauses, and became significantly less active by the end of the allotted time, renewing their efforts mainly in response to negative incentives. These findings are discussed in the light of neurobiological data on gender differences in behaviour

Gliomes de bas grade et plasticité cérébrale : Implications fondamentales et cliniques

La plasticité cérébrale post-lésionnelle (PCPL) décrit l’ensemble des processus permettant au système nerveux central de se réorganiser après une atteinte physique. Depuis l’influent travail de Broca et la prise de pouvoir des modèles « localisationnistes », il est largement admis que la PCPL est limitée, voire impossible, au sein des aires fonctionnelles majeures, dites éloquentes. Pourtant, depuis quelques années, de nouvelles données issues de la chirurgie des gliomes infiltrants de bas-grade (GIBG) sont venues bousculer ce dogme. Il apparaît en effet de plus en plus clairement que des excisions cérébrales massives peuvent être intégralement compensées, pour ne laisser place à aucun déficit fonctionnel détectable. Des techniques d’imagerie pré- et post-chirurgicales, ainsi que des procédures de stimulation peropératoire, permettent de suivre la nature et la cinétique de ces compensations. Celles-ci débutent avant la chirurgie, en réaction à l’invasion tumorale, et se consolident pendant et après la procédure opératoire. Les mécanismes de la compensation pré- et post-lésionnelle impliquent les aires périlésionnelles, les structures cérébrales ipsilatérales distantes et les homologues controlatéraux des zones réséquées. De tels résultats ont d’évidentes implications fondamentales et cliniques, et ouvrent d’importantes perspectives pour la compréhension de la dynamique cérébrale et des phénomènes de plasticité.Post-lesional plasticity (PLP) describes the processes that reorganize cerebral connections after an injury. Since Broca’s influential contribution and the common endorsement of “localisationist” models of brain physiology, it has been widely admitted that PLP was limited, not to say impossible in the so-called “eloquent areas”. However, recent observations associated with the surgical treatments of low grade gliomas have called this dogma into question. Indeed, more and more evidence suggest that large cerebral resections can be compensated so efficiently that no functional deficits can be detected after the surgery. Pre and post surgical investigations based on imaging techniques, as well as intra-surgical investigations involving electrical stimulations, allow to track the nature and the temporal characteristics of these compensations. Compensatory reactions begin before the operation, in response to the tumoral growth. They remain active during and after the surgery. These compensations can involve the perilesional adjacent areas, the distant ipsilateral cerebral structures and the homologous contra-lateral regions. When considered together these results have obvious fundamental and clinical implications. They open new perspectives for understanding cerebral dynamics and the process of brain plasticity

Prehension movements in a patient (AC) with posterior parietal cortex damage and posterior callosal section

Prehension movements of the right hand were recorded in a right-handed man (AC), with an injury to the left posterior parietal cortex (PPC) and with a section of the left half of the splenium. The kinematic analysis of AC’s grasping movements in direct and perturbed con- ditions was compared to that of Wve control subjects. A novel eVect in prehension was revealed—a hemispace eVect—in healthy controls only. Movements to the left hemispace were faster, longer, and with a smaller grasp aperture; perturbation of both object position and distance resulted in the attenuation of the direction eVect on movement time and the time to velocity peak, with a reverse pattern in the time to maximum grip aperture. Nevertheless, the correlation between transport velocity amplitude and grasp aperture remained stable in both perturbed and non-perturbed movements, reXecting the coordination between reaching and grasping in control subjects. In contrast, transport and grasp, as well as their coordination in both direct and perturbed conditions, were negatively aVected by the PPC and sple- nium lesion in AC, suggesting that transport and grasp rely on two functionally identiWable subsystems

Adaptation of eye and hand movements to target displacements of different size

Previous work has documented that the direction of eye and hand movements can be adaptively modified using the double-step paradigm. Here we report that both motor systems adapt not only to small direction steps (5° gaze angle) but also to large ones (28° gaze angle). However, the magnitude of adaptation did not increase with step size, and the relative magnitude of adaptation therefore decreased from 67% with small steps to 15% with large steps. This decreasing efficiency of adaptation may reflect the participation of directionally selective neural circuits in double-step adaptation

Impaired peripheral reaching and on-line corrections in patient DF: optic ataxia with visual form agnosia

An influential model of vision suggests the presence of two visual streams within the brain: a dorsal occipito-parietal stream which mediates action and a ventral occipito-temporal stream which mediates perception. One of the cornerstones of this model is DF, a patient with visual form agnosia following bilateral ventral stream lesions. Despite her inability to identify and distinguish visual stimuli, DF can still use visual information to control her hand actions towards these stimuli. These observations have been widely interpreted as demonstrating a double dissociation from optic ataxia, a condition observed after bilateral dorsal stream damage in which patients are unable to act towards objects that they can recognize. In Experiment 1, we investigated how patient DF performed on the classical diagnostic task for optic ataxia, reaching in central and peripheral vision. We replicated recent findings that DF is remarkably inaccurate when reaching to peripheral targets, but not when reaching in free vision. In addition we present new evidence that her peripheral reaching errors follow the optic ataxia pattern increasing with target eccentricity and being biased towards fixation. In Experiments 2 and 3, for the first time we examined DF’s on-line control of reaching using a double-step paradigm in fixation-controlled and free-vision versions of the task. DF was impaired when performing fast on-line corrections on all conditions tested, similarly to optic ataxia patients. Our findings question the long-standing assumption that DF’s dorsal visual stream is functionally intact and that her on-line visuomotor control is spared. In contrast, in addition to visual form agnosia, DF also has visuomotor symptoms of optic ataxia which are most likely explained by bilateral damage to the superior parietal occipital cortex. We thus conclude that patient DF can no longer be considered as an appropriate single-case model for testing the neural basis of perception and action dissociations

When One Size Does Not Fit All: A Simple Statistical Method to Deal with Across-Individual Variations of Effects

In science, it is a common experience to discover that although the investigated effect is very clear in some individuals, statistical tests are not significant because the effect is null or even opposite in other individuals. Indeed, t-tests, Anovas and linear regressions compare the average effect with respect to its inter-individual variability, so that they can fail to evidence a factor that has a high effect in many individuals (with respect to the intra-individual variability). In such paradoxical situations, statistical tools are at odds with the researcher’s aim to uncover any factor that affects individual behavior, and not only those with stereotypical effects. In order to go beyond the reductive and sometimes illusory description of the average behavior, we propose a simple statistical method: applying a Kolmogorov-Smirnov test to assess whether the distribution of p-values provided by individual tests is significantly biased towards zero. Using Monte-Carlo studies, we assess the power of this two-step procedure with respect to RM Anova and multilevel mixed-effect analyses, and probe its robustness when individual data violate the assumption of normality and homoscedasticity. We find that the method is powerful and robust even with small sample sizes for which multilevel methods reach their limits. In contrast to existing methods for combining p-values, the Kolmogorov-Smirnov test has unique resistance to outlier individuals: it cannot yield significance based on a high effect in one or two exceptional individuals, which allows drawing valid population inferences. The simplicity and ease of use of our method facilitates the identification of factors that would otherwise be overlooked because they affect individual behavior in significant but variable ways, and its power and reliability with small sample sizes (<30–50 individuals) suggest it as a tool of choice in exploratory studies