EEG and neuronavigated single-pulse TMS in the study of the observation/execution matching system: Are both techniques measuring the same process?

It is now well established that the human brain is endowed with a system that matches the observation of actions with their execution. At the motor cortex level, EEG mu rhythm modulation (8–12 Hz) and TMS-induced motor evoked potentials (MEPs) are two techniques commonly used to assess brain activity during action observation. While both techniques have reliably demonstrated similarities in the pattern of activity induced by action production and action observation, the relationship they bear with each other remains elusive. In the present study, we combined ongoing EEG recordings and single-pulse TMS during the execution, imagination and observation of simple hand actions. Relationship between MEPs and EEG frequency bands at the individual level was investigated. Our results replicate those obtained independently with both techniques: a significant increase in MEP amplitude and a significant attenuation of the mu rhythm during action observation, imagination and execution compared to rest. Surprisingly, we found no significant correlation between MEP amplitude and mu rhythm modulation. However, modulation in the low to midrange beta (12–18 Hz) was related to MEP size during the rest and execution conditions. These results suggest that although mu rhythm and TMS-induced MEPs are sensitive to motor resonance mechanisms, they may reflect different processes taking place within the observation/execution matching system.