Temporal dynamics of cortical representation for action

TLDR

Brain‑imaging studies show that Broca’s region and precentral motor cortex are activated during both execution and observation of hand actions, and the mirror system is thought to help us understand others’ actions. The study aimed to clarify the temporal dynamics of cortical activation during execution, imitation, and observation of right‑hand reaching movements ending in a precision pinch. This was investigated using neuromagnetic recordings during execution, online imitation, and observation of the movements. During execution, left BA44 activated first (~250 ms before pinching), followed by left BA4 and then right BA4; during imitation and observation the sequence began in left BA19, with strongest activation during imitation and only occipital activation when observing reaching without pinching, indicating that left BA44 orchestrates the mirror neuron system and is strongly involved in action imitation.

Abstract

Brain-imaging studies have shown that the human Broca's region and precentral motor cortex are activated both during execution of hand actions and during observation of similar actions performed by other individuals. We aimed to clarify the temporal dynamics of this cortical activation by neuromagnetic recordings during execution, on-line imitation, and observation of right-hand reaching movements that ended with a precision pinch of the tip of a manipulandum. During execution, the left inferior frontal cortex [Brodmann's area (BA) 44] was activated first (peak ≈250 ms before the pinching); this activation was followed within 100–200 ms by activation in the left primary motor area (BA4) and 150–250 ms later in the right BA4. During imitation and observation, the sequence was otherwise similar, but it started from the left occipital cortex (BA19). Activation was always strongest during action imitation. Only the occipital activation was detected when the subject observed the experimenter reaching his hand without pinching. These results suggest that the left BA44 is the orchestrator of the human “mirror neuron system” and is strongly involved in action imitation. The mirror system matches action observation and execution and probably contributes to our understanding of actions made by others.