Neural substrates for observing and imagining non-object-directed actions.

The present fMRI study was aimed at assessing the cortical areas active when individuals observe non-object-directed actions (mimed, symbolic, and meaningless), and when they imagine performing those same actions. fMRI signal increases in common between action observation and motor imagery were found in the premotor cortex and in a large region of the inferior parietal lobule. While the premotor cortex activation overlapped that previously found during the observation and imagination of object-directed actions, in the parietal lobe the signal increase was not restricted to the intraparietal sulcus region, known to be active during the observation and imagination of object-directed actions, but extended into the supramarginal and angular gyri. When contrasting motor imagery with the observation of non-object-directed actions, signal increases were found in the mesial frontal and cingulate cortices, the supramarginal gyrus, and the inferior frontal gyrus. The opposite contrast showed activation virtually limited to visual areas. In conclusion, the present data define the common circuit for observing and imagining non-object-directed actions. In addition, they show that the representation of non-object-directed actions include parietal regions not found to be involved in coding object-directed actions.