Activation of human primary motor cortex during action observation: A neuromagnetic study

TLDR

Neural activity in premotor areas during both action execution and observation has been observed in monkeys, and transcranial magnetic stimulation indicates a comparable observation/execution matching system in humans. Using magnetoencephalography, the study measured 15–25 Hz rolandic rebound after median‑nerve stimulation in 10 volunteers during rest, object manipulation, and action observation, with control conditions confirming the effect’s specificity. The 15–25 Hz rebound was strongly suppressed during object manipulation and also significantly reduced during action observation, indicating that the primary motor cortex is engaged when observing others’ movements, which may inform our understanding of action recognition.

Abstract

The monkey premotor cortex contains neurons that discharge during action execution and during observation of actions made by others. Transcranial magnetic stimulation experiments suggest that a similar observation/execution matching system also is present in humans. We recorded neuromagnetic oscillatory activity of the human precentral cortex from 10 healthy volunteers while ( i ) they had no task to perform, ( ii ) they were manipulating a small object, and ( iii ) they were observing another individual performing the same task. The left and right median nerves were stimulated alternately (interstimulus interval, 1.5 s) at intensities exceeding motor threshold, and the poststimulus rebound of the rolandic 15- to 25-Hz activity was quantified. In agreement with previous studies, the rebound was strongly suppressed bilaterally during object manipulation. Most interestingly, the rebound also was significantly diminished during action observation (31–46% of the suppression during object manipulation). Control experiments, in which subjects were instructed to observe stationary or moving stimuli, confirmed the specificity of the suppression effect. Because the recorded 15- to 25-Hz activity is known to originate mainly in the precentral motor cortex, we concluded that the human primary motor cortex is activated during observation as well as execution of motor tasks. These findings have implications for a better understanding of the machinery underlying action recognition in humans.