From gestures to words: Spontaneous verbal labeling of complex sequential hand movements reduces fMRI activation of the imitation-related regions

The association of verbal labels with visuo-spatial patterns and sequences detectably alters neuronal activity in the brain in ways that have yet to be fully characterized. This study investigated the neural substrates involved in the effect of spontaneous verbal labeling on memorizing increasingly complex sequences of hand movements. We used functional magnetic resonance imaging (fMRI) to test our hypothesis that when verbal labels were employed, neuronal activity in imitation-related regions, such as the left inferior frontal gyrus (IFG), would be reduced, whereas without verbal labels, neuronal activation would increase. Sixteen healthy adults satisfactorily performed an immediate imitation task involving six levels of increasing complexity. After the fMRI experiment, participants reported at which complexity level they had formed verbal labels. Based on the self-report, we categorized the task blocks at each complexity level as either with verbal labeling (VL+) or without (VL-). Compared with VL+, the VL- condition activated the left IFG, bilateral middle frontal gyri, left precentral gyrus, and the right angular gyrus, whereas the opposite contrast revealed no significant brain activation. Verbal labeling seems to serve as an efficient heuristic that reduces the cost of cortical activation in the imitation-related regions.