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Successful non-verbal social interaction between human beings requires dynamic and efficient encoding of others' gestures. Our study aimed at identifying neural markers of social interaction and goal variations in a non-verbal task. For this, we recorded simultaneously the electroencephalogram from two participants (dual-EEG), an actor and an observer, and their arm/hand kinematics in a real face-to-face paradigm. The observer watched "biological actions" performed by the human actor and "non-biological actions" performed by a robot. All actions occurred within an interactive or non-interactive context depending on whether the observer had to perform a complementary action or not (e.g., the actor presents a saucer and the observer either places the corresponding cup or does nothing). We analysed the EEG signals of both participants (i.e., beta (~20 Hz) oscillations as an index of cortical motor activity and motor related potentials (MRPs)). We identified markers of social interactions by synchronising EEG to the onset of the actor's movement. Movement kinematics did not differ in the two context conditions and the MRPs of the actor were similar in the two conditions. For the observer, however, an observation-related MRP was measured in all conditions but was more negative in the interactive context over fronto-central electrodes. Moreover, this feature was specific to biological actions. Concurrently, the suppression of beta oscillations was observed in the actor's EEG and the observer's EEG rapidly after the onset of the actor's movement. Critically, this suppression was stronger in the interactive than in the non-interactive context despite the fact that movement kinematics did not differ in the two context conditions. For the observer, this modulation was observed independently of whether the actor was a human or a robot. Our results suggest that acting in a social context induced analogous modulations of motor and sensorimotor regions in observer and actor. Sharing a common goal during an interaction seems thus to evoke a common representation of the global action that includes both actor and observer movements., (© 2013 Elsevier Ltd. All rights reserved.)

We have previously shown that mental rehearsal can replace up to 75% of physical practice for learning a visuomotor task (Allami, Paulignan, Brovelli, & Boussaoud, (2008). Experimental Brain Research, 184, 105-113). Presumably, mental rehearsal must induce brain changes that facilitate motor learning. We tested this hypothesis by recording scalp electroencephalographic activity (EEG) in two groups of subjects. In one group, subjects executed a reach to grasp task for 240 trials. In the second group, subjects learned the task through a combination of mental rehearsal for the initial 180 trials followed by the execution of 60 trials. Thus, one group physically executed the task for 240 trials, the other only for 60 trials. Amplitudes and latencies of event-related potentials (ERPs) were compared across groups at different stages during learning. We found that ERP activity increases dramatically with training and reaches the same amplitude over the premotor regions in the two groups, despite large differences in physically executed trials. These findings suggest that during mental rehearsal, neuronal changes occur in the motor networks that make physical practice after mental rehearsal more effective in configuring functional networks for skilful behaviour., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

We investigated the extent to which the right hemisphere is involved in the control of the ipsilateral hand by analysing the kinematics of right-hand prehension in right brain-damaged (RBD) patients. We required patients to grasp one of five possible objects, equally-sized and distributed over a 40 degrees wide workspace. With the purpose of investigating the right hemisphere contribution to the on-line visuo-motor control, we also assessed patients' ability to correct their movement "in-flight", in response to a sudden change of object position. Patients' performance was compared to that of aged-matched controls. A Younger group of healthy subjects, matching the population classically tested on double-step paradigms, was also evaluated to fully assess whether patients' kinematics could be partially due to normal ageing. As a further aim, the possible influence of hemispatial neglect was evaluated by comparing the performances of right brain-damaged patients with and without neglect. In normal subjects, the results confirmed and extended the notion of (a). positional tuning of grip formation, and (b). fast reactions following a change in object position. In addition, subtle effects of ageing on visuo-motor behaviour were shown by less efficient movement correction in the Elderly group. Patients executing reach-to-grasp actions into the left contralesional hemispace were selectively affected in both temporal and spatial aspects of movements. While their performances were relatively well preserved in the right hemispace, patients did not show positional tuning of grip formation, nor fast corrections of their movements when acting in the left hemispace. Interestingly, similar deficits were found irrespective of the presence of neglect. These results show that the right hemisphere contributes to the processing of visuo-motor information that is necessary for executing actions with the ipsilateral hand in the contralateral space.

With the help of kinematic analysis, the temporal organization of the complex daily activity 'drinking from a bottle with a glass' was described in detail. The analysis focused on the sequential action structure, the prehensile acts, and the bimanual coordination as well as on the effect of different instruction modalities on these parameters to explore the underlying representation for this complex action. Movements of the two arms were recorded in three-dimensional space with the help of an optoelectronic device in 12 normal subjects under four conditions: (1) action pantomime after verbal instruction; (2) action imitation after observation of the action performed by the experimenter without the objects; (3) action pantomime while seeing, but not touching the objects; and finally (4) action execution with objects. Despite high execution variability, the temporal structure of the action could be precisely described by the relative duration and peak velocity of action segments, by the MGA-object size-correlation, and by linear regression analysis between the onsets of functionally related action segments. A similar structure of the action as characterized by these kinematic parameters was retained across different instruction modalities. Only when the action was executed with the objects, the interval between the movement onsets of either hand and the peak velocity of the manipulative acts were reduced, while no change was observed across the other three instruction modalities. This stability of the temporal structure suggests the existence of a level in the representation of an action where all the modalities converge.