Sensorimotor integration in sequential manual actions: shared parietal activation across planning, execution and observation.

Sequential manual actions involving object manipulation, whether performed ourselves or observed in others, are a fundamental part of our daily lives. Motor representations within internal action models have been linked to both action execution and observation, but it is less clear how brain activity associated with planning, execution and observation of complex sequential actions differs and overlap. Here, using event-related fMRI, we examined brain activity during sequential manual action in planning, execution and observation in a sample of healthy adults (N = 28). Comparing actions under different task complexity (complex, rotation > baseline, no rotation), we found increased activation in parietal, precentral and sensory-motor regions during action execution planning. Execution of complex actions engaged ipsilateral parieto-frontal regions, while observation activated parietal regions. Planning to observe complex actions engaged occipito-parietal, precentral and cerebellar regions. Importantly, across all four conditions, we found a significant overlap in brain activity in the bilateral intraparietal sulcus. This suggests that the inferior parietal lobe is an important node for complex sequential manual actions.