Simultaneous action execution and observation optimise grasping actions

Action observation and execution share overlapping neural resonating mechanisms. In the present study, we sought to examine the effect of the activation of this system during concurrent movement observation and execution in a prehension task, when no a priori information about the requirements of grasping action was available. Although it is known that simultaneous activation by observation and execution influences motor performance, the importance of the delays of these two events and the specific effect of movement observation itself (and not the prediction of the to-be-observed movement) on action performance are poorly known. Fine-grained kinematic analysis of both the transport and grasp components of the movement should provide knowledge about the influence of movement observation on the precision and the performance of the executed movement. The experiment involved two real participants who were asked to grasp a different side of a single object that was composed of a large and a small part. In the first experiment, we measured how the transport component and the grasp component were affected by movement observation. We tested whether this influence was greater if the observed movement occurred just before the onset of movement (200 ms) or well before the onset of movement (1 s). In a second experiment, to reproduce the previous experiment and to verify the specificity of the grasping movements, we also included a condition consisting of pointing towards the object. Both experiments showed two main results. A general facilitation of the transport component was found when observing a simultaneous action, independent of its congruency. Moreover, a specific facilitation of the grasp component was present during the observation of a congruent action when movement execution and observation were nearly synchronised. While the general facilitation may arise from a competition between the two participants as they reached for the object, the specific facilitation of the grasp component seems to be directly related to mirror neuron system activity induced by action observation itself. Moreover, the time course of the events appears to be an essential factor for this modulation, implying the transitory activation of the mirror neuron system.