Motor resonance in monkey parietal and premotor cortex during action observation: Influence of viewing perspective and effector identity

Observing others performing motor acts like grasping has been shown to elicit neural responses in the observer's parieto-frontal motor network, which typically becomes active when the observer would perform these actions him/herself. While some human studies suggested strongest motor resonance during observation of first person or egocentric perspectives compared to third person or allocentric perspectives, other research either report the opposite or did not find any viewpoint-related preferences in parieto-premotor cortices. Furthermore, it has been suggested that these motor resonance effects are lateralized in the parietal cortex depending on the viewpoint and identity of the observed effector (left vs right hand). Other studies, however, do not find such straightforward hand identity dependent motor resonance effects. In addition to these conflicting findings in human studies, to date, little is known about the modulatory role of viewing perspective and effector identity (left or right hand) on motor resonance effects in monkey parieto-premotor cortices. Here, we investigated the extent to which different viewpoints of observed conspecific hand actions yield motor resonance in rhesus monkeys using fMRI. Observing first person, lateral and third person viewpoints of conspecific hand actions yielded significant activations throughout the so-called action observation network, including STS, parietal and frontal cortices. Although region-of-interest analysis of parietal and premotor motor/mirror neuron regions AIP, PFG and F5, showed robust responses in these regions during action observation in general, a clear preference for egocentric or allocentric perspectives was not evident. Moreover, except for lateralized effects due to visual field biases, motor resonance in the monkey brain during grasping observation did not reflect hand identity dependent coding.