Is Broca's Area Crucial for Imitation?

Some neuroimaging studies have reported activation by imitation in the left Brodmann area 44 (BA 44), a part of Broca's area considered to be a neural substrate for speech production. However, in these previous studies the subjects were required to perform the same movements repeatedly so that the experimental stimuli could be viewed as cues when to do the given movements rather than a specification of what to do. Activation in the left BA 44 has also been observed in delayed motor execution tasks. This may confound the activity in BA 44 for imitation tasks used in the former studies. We tested the involvement of bilateral BA 44 and BA 45 in imitation and delayed execution tasks by functional magnetic resonance imaging with cytoarchitectonically defined BA 44 and BA 45 as volumes of interest. Our tasks required the subjects to perform a transformation from visual information (photographs of hand postures or symbolic specification of the postures) into a new hand movement in each trial. A three-way analysis of variance was performed with factors instruction, execution timing and area. The results revealed significant main effect by execution timing and by area, but not by instruction. We conclude that Broca's area does not play a pivotal role in imitation.