The social cognitive dimension of pantomime.

Pantomime production is commonly interpreted as reflecting tool-use-related cognitive processes. Yet, in everyday life, pantomime deserves a communication function and the exaggeration of amplitude found during pantomime compared to real tool use may reflect the individual's attempt to communicate the intended gesture. Therefore, the question arises about whether pantomime is a communicative behavior that is nevertheless supported only by non-social cognitive processes. We contribute to answering this question by using kinematic analyses. Participants performed the pantomime of using a saw or a hammer from visual presentation in three conditions: Free (no specific instructions), Self (focus on the real tool-use action), and Others (focus on the communicative dimension). Finally, they used the tool with the corresponding object (Actual condition). Participants' social cognition were assessed using gold standard questionnaires. Our results indicated that the manipulation of instructions had a minor effect on the exaggeration of amplitude during pantomime. We reported a link between the social cognition score and the amplitude in the Others condition for the hammer, which suggests that social cognitive processes could take part in pantomime production in some conditions. Nevertheless, this result does not alter our conclusion that social cognitive processes might be far from necessary for pantomime production.

Non-invasive brain stimulation shows possible cerebellar contribution in transfer of prism adaptation after-effects from pointing to throwing movements.

Whether sensorimotor adaptation can be generalized from one context to others represents a crucial interest in the field of neurological rehabilitation. Nonetheless, the mechanisms underlying transfer to another task remain unclear. Prism Adaptation (PA) is a useful method employed both to study short-term plasticity and for rehabilitation. Neuro-imaging and neuro-stimulation studies show that the cerebellum plays a substantial role in online control, strategic control (rapid error reduction), and realignment (after-effects) in PA. However, the contribution of the cerebellum to transfer is still unknown. The aim of this study was to test whether interfering with the activity of the cerebellum affected transfer of prism after-effects from a pointing to a throwing task. For this purpose, we delivered cathodal cerebellar transcranial Direct Current Stimulation (tDCS) to healthy participants during PA while a control group received cerebellar Sham Stimulation. We assessed longitudinal evolutions of pointing and throwing errors and pointing trajectories orientations during pre-tests, exposure and post-tests. Results revealed that participants who received active cerebellar stimulation showed (1) altered error reduction and pointing trajectories during the first trials of exposure; (2) increased magnitude but reduced robustness of pointing after-effects; and, crucially, (3) slightly altered transfer of after-effects to the throwing task. Therefore, the present study confirmed that cathodal cerebellar tDCS interferes with processes at work during PA and provides evidence for a possible contribution of the cerebellum in after-effects transfer.

Prisms to Shift Pain Away: Pathophysiological and Therapeutic Exploration of CRPS with Prism Adaptation.

Complex Regional Pain Syndrome (CRPS) is an invalidating chronic condition subsequent to peripheral lesions. There is growing consensus for a central contribution to CRPS. However, the nature of this central body representation disorder is increasingly debated. Although it has been repeatedly argued that CRPS results in motor neglect of the affected side, visual egocentric reference frame was found to be deviated toward the pain, that is, neglect of the healthy side. Accordingly, prism adaptation has been successfully used to normalize this deviation. This study aimed at clarifying whether 7 CRPS patients exhibited neglect as well as exploring the pathophysiological mechanisms of this manifestation and of the therapeutic effects of prism adaptation. Pain and quality of life, egocentric reference frames (visual and proprioceptive straight-ahead), and neglect tests (line bisection, kinematic analyses of motor neglect and motor extinction) were repeatedly assessed prior to, during, and following a one-week intense prism adaptation intervention. First, our results provide no support for visual and motor neglect in CRPS. Second, reference frames for body representations were not systematically deviated. Third, intensive prism adaptation intervention durably ameliorated pain and quality of life. As for spatial neglect, understanding the therapeutic effects of prism adaptation deserves further investigations.

Effect of juggling expertise on pointing performance in peripheral vision.

Juggling is a very complex activity requiring motor, visual and coordination skills. Expert jugglers experience a "third eye" monitoring leftward and rightward ball zenith positions alternately, in the upper visual fields, while maintaining their gaze straight-ahead. This "third eye" reduces their motor noise (improved body stability and decrease in hand movement variability) as it avoids the numerous head and eye movements that add noise into the system and make trajectories more uncertain. Neuroimaging studies have shown that learning to juggle induces white and grey matter hypertrophy at the posterior intraparietal sulcus. Damage to this brain region leads to optic ataxia, a clinical condition characterised by peripheral pointing bias toward gaze position. We predicted that expert jugglers would, conversely, present better accuracy in a peripheral pointing task. The mean pointing accuracy of expert jugglers was better for peripheral pointing within the upper visual field, compatible with their subjective experience of the "third eye". Further analyses showed that experts exhibited much less between-subject variability than beginners, reinforcing the interpretation of a vertically asymmetrical calibration of peripheral space, characteristic of juggling and homogenous in the expert group. On the contrary, individual pointing variability did not differ between groups neither globally nor in any sector of space, showing that the reduced motor noise of experts in juggling did not transfer to pointing. It is concluded that the plasticity of the posterior intraparietal sulcus related to juggling expertise does not consist of globally improved visual-to-motor ability. It rather consists of peripheral space calibration by practicing horizontal covert shifts of the attentional spotlight within the upper visual field, between left and right ball zenith positions.

Feeling without localizing: exploring tactile misperception in a patient with uncommon parietal left brain damage.

Introduction: We report a very unique clinical presentation of a patient who complained, after a left parietal brain damage, about feeling tactile stimulations on his right upper limb without being able to localize them. Methods: Using a single case study approach, we report three experiments relying on several custom-made tasks to explore the different levels of somatosensory information processing, ranging from somato-sensation to somato-representation. Results: Our results showed a preserved ability to localize tactile stimuli applied on the right upper limb when using pointing responses while the ability to localize was less efficient when having to name the stimulated part (akin Numbsense). When the stimuli were applied on more distal locations (i.e., on the hand and on fingers), the number of correct responses decreased significantly independently of the modality of response. Finally, when visually presented with a stimulus delivered on the hand of an examiner in synchrony with the stimulation on the hidden hand of the patient, responses were largely influenced by the visual information available. Altogether, the convergence of these different customized tasks revealed an absence of autotopagnosia for motor responses for the right upper limb, associated with altered abilities to discriminate stimulus applied on distal and restricted/closer zones in the hand. Discussion: The somato-representation of our patient seemed to significantly rely on visual information, leading to striking deficits to localize tactile stimuli when vision and somesthesic afferences are discordant. This case report offers a clinical illustration of pathological imbalance between vision and somesthesia. Implications of these troubles in somato-representation on higher cognitive level processes are discussed.

Does anodal cerebellar tDCS boost transfer of after-effects from throwing to pointing during prism adaptation?

Prism Adaptation (PA) is a useful method to study the mechanisms of sensorimotor adaptation. After-effects following adaptation to the prismatic deviation constitute the probe that adaptive mechanisms occurred, and current evidence suggests an involvement of the cerebellum at this level. Whether after-effects are transferable to another task is of great interest both for understanding the nature of sensorimotor transformations and for clinical purposes. However, the processes of transfer and their underlying neural substrates remain poorly understood. Transfer from throwing to pointing is known to occur only in individuals who had previously reached a good level of expertise in throwing (e.g., dart players), not in novices. The aim of this study was to ascertain whether anodal stimulation of the cerebellum could boost after-effects transfer from throwing to pointing in novice participants. Healthy participants received anodal or sham transcranial direction current stimulation (tDCS) of the right cerebellum during a PA procedure involving a throwing task and were tested for transfer on a pointing task. Terminal errors and kinematic parameters were in the dependent variables for statistical analyses. Results showed that active stimulation had no significant beneficial effects on error reduction or throwing after-effects. Moreover, the overall magnitude of transfer to pointing did not change. Interestingly, we found a significant effect of the stimulation on the longitudinal evolution of pointing errors and on pointing kinematic parameters during transfer assessment. These results provide new insights on the implication of the cerebellum in transfer and on the possibility to use anodal tDCS to enhance cerebellar contribution during PA in further investigations. From a network approach, we suggest that cerebellum is part of a more complex circuitry responsible for the development of transfer which is likely embracing the primary motor cortex due to its role in motor memories consolidation. This paves the way for further work entailing multiple-sites stimulation to explore the role of M1-cerebellum dynamic interplay in transfer.

Constraint therapy versus intensive training: implications for motor control and brain plasticity after stroke.

Many studies have demonstrated that constraint induced movement therapy (CIMT) improves upper limb motor impairment following stroke. This rehabilitation method combines constraint of the less-affected upperlimb with intensive training of the paretic limb. The aim of the present study was to evaluate, in a single case study, the respective effects of each of these two therapeutic interventions. The patient selected was a 32-year-old right-handed woman. Three and a half years prior to inclusion, she suffered a left capsular infarct responsible for a right hemiparesis. Several assessments were carried out before and after constraint therapy and then after intensive training. Each assessment included measures of hand function as well as a three-dimensional (3D) analysis of prehension. Results showed a significant improvement of motor performance after the constraint period and an additional amelioration after the intensive training period. Kinematic analysis showed that the transport phase of movement (movement time and velocity peaks) was improved after the constraint period, whereas the grasping phase (maximum grip aperture) was modified after intensive training. These data could reflect a specific effect of treatment on each phase of the prehension task, or a more general proximal-to-distal gradient of recovery. Although firm conclusions are not warranted on the basis of this single case study, we confirm the utility of 3D motion analysis to evaluate objectively the effectiveness of a therapeutic intervention. We also discuss the implications of our findings for understanding processes of motor control reorganisation.

Inter-task transfer of prism adaptation depends on exposed task mastery.

The sensorimotor system sets up plastic alterations to face new demands. Terms such as adaptation and learning are broadly used to describe a variety of processes underlying this aptitude. The mechanisms whereby transformations acquired to face a perturbation generalize to other situations or stay context-dependent remain weakly understood. Here, we compared the performance of hand pointing vs throwing to visual targets while facing an optical shift of the visual field (prismatic deviation). We found that the transfer of compensations was conditioned by the task performed during exposure to the perturbation: compensations transferred from pointing to throwing but not at all from throwing to pointing. Additionally, expertise on the task performed during exposure had a marked influence on the amount of transfer to the non-exposed task: throwing experts (dart players) remarkably transferred compensations to the pointing task. Our results reveal that different processes underlying these distinct transfer properties may be at work to face a given perturbation. Their solicitation depends on mastery for the exposed task, which is responsible for different patterns of inter-task transfer. An important implication is that transfer properties, and not only after-effects, should be included as a criterion for adaptation. At the theoretical level, we suggest that tasks may need to be mastered before they can be subjected to adaptation, which has new implications for the distinction between learning and adaptation.

Tool Use and Generalized Motor Programs: We All Are Natural Born Poly-Dexters.

For most people, human tool use is inextricably entwined with manual dexterity. This folk belief is widespread among scientists too. In this line, human tool use is based on motor programs about how the hand interacts with tools, implying that the use of end-effectors other than the hand should generate motor control difficulties (e.g., inability to reproduce a specific tool-use action over time), because these so-called programs characterize the spatiotemporal parameters of hand movements, but not of other end-effectors. To test this, we asked participants to perform three tool-use actions (e.g., pounding a nail) with four end-effectors (i.e., right foot, right elbow, left hand, right hand). We show that participants not only spontaneously performed the tool-use actions effectively, but also crucially kept tools' spatiotemporal parameters constant among the end-effectors. This phenomenon, which we call poly-dexterity, is at odds with the view that the human brain stores hand-centered motor programs for tool use. Poly-dexterity is instead consistent with the idea that, once the tool-use action is formed mentally, general motor programs can be applied to a variety of end-effectors. Reversing the usual evolutionary perspective, our findings support that, in the course of evolution, manual dexterity has come after tool-use skills.

Complex regional pain syndrome associated with hyperattention rather than neglect for the healthy side: A comprehensive case study.

Complex regional pain syndrome (CRPS) is a dehabilitating chronic condition occurring with peripheral lesions. There is growing consensus for a central contribution to CRPS. Although the nature of this central body representation disorder is increasingly debated, it has been repeatedly argued that CRPS results in motor neglect of the affected side. The present article describes a comprehensive and quantitative case report demonstrating that: (1) not all patients with chronic CRPS exhibit decreased spatial attention for the affected side and (2) patients may actually exhibit a substantial, broad and reliable attentional bias toward the painful side, akin to spatial neglect for the healthy side. This unexpected result agrees with the idea that patients can be hyper-attentive toward their pathological side as a manifestation of lowered pain threshold, allodynia and kinesiophobia.

Muscle Activation during Gait in Children with Duchenne Muscular Dystrophy.

The aim of this prospective study was to investigate changes in muscle activity during gait in children with Duchenne muscular Dystrophy (DMD). Dynamic surface electromyography recordings (EMGs) of 16 children with DMD and pathological gait were compared with those of 15 control children. The activity of the rectus femoris (RF), vastus lateralis (VL), medial hamstrings (HS), tibialis anterior (TA) and gastrocnemius soleus (GAS) muscles was recorded and analysed quantitatively and qualitatively. The overall muscle activity in the children with DMD was significantly different from that of the control group. Percentage activation amplitudes of RF, HS and TA were greater throughout the gait cycle in the children with DMD and the timing of GAS activity differed from the control children. Significantly greater muscle coactivation was found in the children with DMD. There were no significant differences between sides. Since the motor command is normal in DMD, the hyper-activity and co-contractions likely compensate for gait instability and muscle weakness, however may have negative consequences on the muscles and may increase the energy cost of gait. Simple rehabilitative strategies such as targeted physical therapies may improve stability and thus the pattern of muscle activity.

Dopa-Responsive Dystonia and gait analysis: A case study of levodopa therapeutic effects.

INTRODUCTION: Patients suffering Dopa-Responsive Dystonia present dystonia, abnormal postural balance and gait impairment. Treatment with levodopa typically improves these three symptoms. The present study provides an extensive analysis of gait and posture in a patient with Dopa-Responsive Dystonia, prior to and during levodopa therapy. METHOD: The patient was assessed with the Unified Dystonia Rating Scale, underwent motion analysis with an optoelectronic system and postural analysis with force plates. RESULTS: This study provides a detailed quantification of gait parameters in a Dopa-Responsive Dystonia patient. Prior to treatment, mean walking speed was severely reduced, gait cadence and step length were decreased and stride width was increased. Right lower limb and pelvis showed kinematic defects, trunk and Centre of Mass were backwards. During levodopa therapy, the walking speed was doubled, gait cadence and step length were increased and stride width was reduced. Nearly all kinematic parameters of lower limbs were significantly improved. The patient's Centre of Mass during gait and Centre of pressure in static position both shifted forward. CONCLUSION: Levodopa dramatically decreased dystonia and improved spatio-temporal, kinematic and posture parameters. Our main pathophysiological hypothesis is that trunk tilt and its consequences on the Centre of Mass position have a pivotal influence on gait and balance, explaining both the initial impairments and the therapeutic effects. Gait analysis proves to be an effective tool to understand the pathophysiology of this patient, the therapeutic effects and mild residual gait defects in order to plan further rehabilitation strategy for this DRD patient. We propose that it will also prove to be useful for the exploration of other dystonic patients.

Objective evaluation of body displacements during activities using the wearable inertial system ActimedARM.

This paper presents an algorithm for the objective assessment of the motion of a body during health-evaluation physical tests using our inertial sensor, namely the ActimedARM. With the orientation quaternions provided by the sensor and integrating twice the calibrated acceleration measurements, we are able to compute the displacement of the sensor worn by a patient. To validate our data we have made measurements with both our sensor and a reference optical system. The displacement curves provided by our algorithm were correlated to the gold-standard system with a mean rate of 94.96%.

Testing for optic ataxia in a blind field.

Optic ataxia is a component of Balint's syndrome and is a disorder that results from damage to the posterior parietal cortex (PPC) leading to deficits in reaching and grasping objects presented in the visual field opposite to the damaged hemisphere. It is also often the case that Balint's syndrome is accompanied by visual field defects due to the proximity of parietal and occipital cortices and also due to the subcortical pathway relaying visual information from the retina to the visual cortex passing underneath the parietal cortex. The presence of primary visual defects such as hemianopia often prevents clinicians from diagnosing higher-level visual deficits such as optic ataxia; the patient cannot reach to targets he/she cannot see. Here, we show that through the use of a paradigm that takes advantage of remapping mechanisms, we were able to observe optic ataxia in the blind field. We measured reach endpoints of a patient presenting with left optic ataxia as well as a quadrantanopia in the left lower visual field in eye-static and eye-dynamic conditions. In static conditions, we first asked the patient to reach to targets viewed in her non-optic ataxic intact right visual field (fixating on the left of the target array). In this case, the patient showed undershoots equivalent to controls. Next, we asked her to reach to (the same) targets viewed in the upper left optic ataxic but intact visual field (fixating to the right of the target array). The undershooting pattern increased greatly, consistent with unilateral left optic ataxia. In dynamic conditions, we asked her to view targets in her good (right lower) visual field before reorienting her line of sight to the opposite side, causing the internal representation of the target to be updated into the opposite (ataxic) blind visual field. The patient then reached to the remembered (and updated) location of the target. We found errors typical of optic ataxia for reaches guided toward the quadrantanopic field. This confirmed that reaching errors depended on the updated internal representation of the target and not on where the target was viewed initially. In both the patient and the controls, the updating of target location was partial, with reaching errors observed subsequent to an eye movement made from left to right fixation positions being intermediate between the left and right static conditions. Thus, using this remapping paradigm, we were able to observe optic ataxia in the blind field. In conclusion, this remapping paradigm would allow clinicians to test for visuo-manual transformation deficits (optic ataxia) even when it is associated with hemianopia.