Seeing action simulation as it unfolds: The implicit effects of action scenes on muscle contraction evidenced through the use of a grip-force sensor.

Action simulation is a cognitive process that mentally simulates a motor act without performing it in the true external world. Simulation mechanisms play a key role in perceiving, feeling and understanding actions executed by others. However, very little is known about the process dynamics because of the absence of a behavioral tool to probe directly the action simulation process as it unfolds. Twenty-seven healthy adults were required to hold a force sensor in a relaxed pinch-grip while viewing action videos of different intensities: wait (null); touch (low); move (medium); crush (high). When contrasting the variations in grip force (GFv) across conditions, results indicated that GFv started to increase and peaked respectively 200 and 400 ms after the moment of effector-object contact. In the wait condition, GFv remained flat throughout the trial confirming an absence of simulation engagement. Peak GFv was greater for the high and medium than for the low intensity videos suggesting greater brain activity overflow to the peripheral motor system when simulating more effortful body movements. These effects were negatively correlated with the motor imagery abilities of the participants, with greater GFv in the poor imagers as determined by the Movement Imagery Questionnaire. Our results confirm the possibility of using a non-invasive grip force sensor to detect not only when individuals are cognitively engaged in action simulation but also to reveal the dynamics of the process. With various sets of videos, this paradigm offers new perspectives in the study of action simulation and its role in human cognition.

Association between motor timing and treatment outcomes in patients with alcohol and/or cocaine use disorder in a rehabilitation program.

BACKGROUND: Individuals with Substance Use Disorders (SUDs) have disruptions in the brain's dopaminergic (DA) system and the functioning of its target neural substrates (striatum and prefrontal cortex). These substrates are important for the normal processing of reward, inhibitory control and motivation. Cognitive deficits in attention, impulsivity and working memory have been found in individuals with SUDs and are predictors of poor SUD treatment outcomes and relapse in alcohol and cocaine dependence specifically. Furthermore, the DA system and accompanying neural substrates play a key role in the timing of motor acts (motor timing). Motor timing deficits have been found in DA system related disorders and more recently also in individuals with SUDs. Motor timing is found to correlate with attention, impulsivity and working memory deficits. To our knowledge motor timing, with regards to treatment outcome and relapse, has not been investigated in populations with SUDs. METHODS/DESIGN: This study aims to investigate motor timing and its relation to treatment response (at 8 weeks) and relapse (at 12 months) in cocaine and/or alcohol dependent individuals. The tested sensitivity values of motor timing parameters will be compared to a battery of neurocognitive tests, owing to the novelty of the motor task battery, the confounding effects of attention and working memory on motor timing paradigms, and high impulsivity levels found in individuals with SUDs. DISCUSSION: This research will contribute to current knowledge of neuropsychological deficits associated with treatment response in SUDs and possibly provide an opportunity to individualize and modify currently available treatments through the possible prognostic value of motor task performance in cocaine and/or alcohol dependent individuals.

[Production of rhythms in schizophrenia: the central role of attention]. / Production de rythmes dans la schizophrénie : rôle central de l'attention.

BACKGROUND: Schizophrenia is a psychiatric illness that is characterised by a deficit in the fluent sequencing of thought and action. This problem of discoordination might be due to unreliable timing processes associated with a difficulty in allocating sufficient attention. In the present study, we placed ourselves within the hypothesis that schizophrenic patients may have difficulties in producing rhythmic tapping actions and that this deficit may be correlated with the degree of attention abnormalities. METHOD: Subjects were required to tap in rhythm with alternating force levels and/or alternating time intervals (<1s) during trials lasting 24s. In addition, all patients performed an attention task (D2 test). A qualitative analysis of the tap trials was conducted in order to characterise the nature of the deficits that patients revealed. RESULTS: Results showed that all patients revealed significant difficulties in performing the tapping trials. The number of trials removed was correlated with the level of attention dysfunction. Finally, our qualitative analysis revealed that 60% of patients presented attentional lapses - which were never observed in the healthy controls. CONCLUSION: This study revealed deficits in the timing of action that resemble, at least on a behaviour level, the clinical lapses observed in schizophrenia. These lapses seem to be correlated to the degree of attention deficits. Future studies are now required in order to gain better understanding of the nature of the attention deficits in schizophrenia. More specifically, a better definition of the possible functional relationship between clinical lapses, cognitive lapses and action freezing is needed to develop innovating tools for rehabilitation.

[Sense of agency: experiencing is not judging]. / Agentivité: se vivre ou se juger agent?

INTRODUCTION: Experiencing oneself as the author of an action defines the sense of agency, which is a component of the self. A deficit affecting this process is thought to cause the principle symptoms characterizing schizophrenia - e.g. delusions of control and auditive hallucinations would exist because patients do not experience themselves as the author of their own actions. LITERATURE FINDINGS: To explore this specific problem of the sense of agency in schizophrenia, Frith et al. collected a serie of experimental data that lead them to propose that the sense of agency relied on the automatic motor system, processes that enable the predictive adjustment of action. An impairment in these processes (called <> in the literature) would lead to the problem of dissociation between our own actions and those performed by others. More specifically, the problem would lay in the comparison between the predicted state and the desired state (figure 1). Jeannerod et al. from Lyon used attribution judgements that suggested that the sense of agency would not depend uniquely on the motor mechanisms but would also involve conscious processes. Recently, Frith et al. have published new data that integrates both preceding models. According to this theory, the sense of agency would depend on the processes involved in the predictive control of action but at a conscious level: the attenuation of the sensory feedback, specific of our own actions. This attenuation would depend on the accuracy of comparison between the predicted state and the actual state. Moreover, the sense of agency would also imply the management of social frame, which normally gives the means to cope with human interaction. DISCUSSION: The conception of the sense of agency has greatly evolved over the years, mainly because of the various experimental methods employed. The consequences of this are the various theoretical interpretations given to the characteristics of the sense of agency. They can be explained in two main points: a non-unified definition of the sense of agency and an absence of experimental data testing alternative interpretations. First, protocols using attribution judgements have proven to be useful to gain better understanding of the attribution mechanism in schizophrenia. However, findings obtained with these judgments have often been used to conclude on deficits of the sense of agency in schizophrenia, whereas the sense of agency is only a sub component of these judgements. CONCLUSION: More work must be conducted in order to show that generalization from judgements to self-agency is possible. Secondly, data have not been collected in order to go against the accepted proposition that the sense of agency (1) implies conscious processes, comes (2) secondary to action execution because based on sensory attenuation and (3) has subjective consequences only. Further studies would be useful to explore these points, so as to improve our understanding of the physiopathologyogy of schizophrenia.

Efficiency of grip force adjustments for impulsive loading during imposed and actively produced collisions.

During object manipulation, both predictive feedforward and reactive feedback mechanisms are available to adjust grip force (GF) levels to compensate for the destabilizing effects of load force changes. During collisions, load force increases impulsively (< 20 ms). Thus, only predictive control of GF can be used to ensure grasp stabilization. A collision paradigm is here used to investigate the effects of practice and vision on the efficiency of the predictive control of GF. Subjects actively produced or received an imposed collision with a pendulum. Subjects were more efficient (used smaller GF for identical loads) when producing than when receiving the collisions. Effects of practice were evident in the active producing task only, with GF levels reducing over repetitions, suggesting that sensorimotor memory for the task was used to adjust GF more efficiently. With imposed collisions, GF levels did not reduce with repetition, which suggests that a direct relation between motor action and sensory feedback may be necessary to improve efficiency. Nevertheless, in this condition GF was lower with visual feedback, indicating potential for more efficient grip possibly associated with subjects degree of confidence. We discuss the implications of these results for accounts of the predictive and the reactive control of movement.