Motor awareness modulates the temporal representation of the action

Anosognosia for hemiplegia (AHP) refers to patients’ inability to appreciate their hemi-paralysis after right-hemisphere damage. This negatively impacts on rehabilitation outcome due to lack of motivation. Although action observation modulates the AHP symptoms, the relationship between unawareness and action representation is not clear. Here we explored the relationship between motor awareness and the temporal representation of actions. 25 right (LBD) and left (RBD) hemiplegic patients (6 AHP) and 35 healthy controls were recruited. The neuropsychological assessment controlled for cognitive deficits. In the experimental task (Action Time Estimation–ATE) videos of actions with objects were presented in two conditions: i) hands performing actions; ii) objects moving without effector. In two control tasks, videos showed a ball moving toward a bar and a still circle. The durations of the videos were 3000ms, 4500ms, 6500ms. Participants were asked to estimate the video duration on a 0-8 seconds scale. When the hand was shown, AHP patients performed like controls, while RBD and LBD patients underestimated the action duration. Yet, RBD and AHP patients’ performances did not differ from controls’ in control tasks. LBD group underestimated the duration in all the tasks. These results suggest that motor-awareness deficits modulate the temporal representation of actions. While RBD did not accurately estimate the action video durations compared to controls, AHP showed the opposite pattern, indicating that unawareness prevents of action representations according to the current body-state and abilities. Control tasks excluded the possibility of a general time estimation deficit, which could be instead present in LBD group.