Actions or hand-object interactions? Human inferior frontal cortex and action observation.

Cells in macaque ventral premotor cortex (area F5c) respond to observation or production of specific hand-object interactions. Studies in humans associate the left inferior frontal gyrus, including putative F5 homolog pars opercularis, with observing hand actions. Are these responses related to the realized goal of a prehensile action or to the observation of dynamic hand movements? Rapid, event-related fMRI was used to address this question. Subjects watched static pictures of the same objects being grasped or touched while performing a 1-back orienting task. In all 17 subjects, bilateral inferior frontal cortex was differentially activated in response to realized goals of observed prehensile actions. Bilaterally, precentral gyrus was most frequently activated (82%) followed by pars triangularis (73%) and pars opercularis (65%).