Awareness affects motor planning for goal-oriented actions.

We studied pre-movement cortical activity related to praxic actions performed at self-paced rate and having ecological meanings and functions. Motor-related cortical potentials were recorded using 64-channels EEG in two experiments. Experiment 1 included 15 subjects performing in separate blocks two object-oriented actions: grasping a tea-cup and impossible grasping of a tea-cup (same goal but the grasp was mechanically hindered). Experiment 2 included a subset of 7 subjects from Exp. 1 and the action was reaching a tea-cup; this control condition had a different goal but was kinematically similar to impossible grasping. Different activity patterns in terms of onset, amplitude, duration and, at least in part, sources were recorded in the preparation phase (BP component) according to the specific action and to the possibility of accomplishing it. The main result is that parietal areas were involved in grasping preparation (called "posterior" BP) and not in reaching and impossible grasping preparation. The anterior frontal-central activity (called "anterior" BP) during preparation for grasping started earlier than the other two conditions. The cortical activity during preparation for reaching was similar to that for impossible grasping, except for a frontal activity only detected in the latter condition. It is concluded that the action preparation, even in its early phase, is affected by action meaning and by the awareness of being able to perform the requested action.