What is "mirror" in the Premotor Cortex? A Review

We review the findings of 24 fMRI studies examining activations in the premotor cortex (Brodmann's areas 6 and 44) during passive observation of actions. We found that such activations regularly occurred. Looking for functional differentiation in the premotor cortex, we found that one parameter was associated with systematic differences in location: this was the presence or absence of targets. Observing biological actions with a physical target, compared to a visual control showing no action at all, consistently activated the ventral premotor cortex (BA 6), and did so significantly more than observing target-less actions (with the same control). In contrast, the activity in BA 44 ("Broca's area") was not modulated by the presence or absence of targets. We propose that the ventral precentral gyrus, and not BA 44, shares the visual properties of "mirror" neurons found in area F5 of the macaque brain.