Motor imagery drives the effects of combined action observation and motor imagery on corticospinal excitability for coordinative lower-limb actions.

Combined action observation and motor imagery (AOMI) facilitates corticospinal excitability (CSE) and may potentially induce plastic-like changes in the brain in a similar manner to physical practice. This study used transcranial magnetic stimulation (TMS) to explore changes in CSE for AOMI of coordinative lower-limb actions. Twenty-four healthy adults completed two baseline (BL, BL) and three AOMI conditions, where they observed a knee extension while simultaneously imagining the same action (AOMI), plantarflexion (AOMI), or dorsiflexion (AOMI). Motor evoked potential (MEP) amplitudes were recorded as a marker of CSE for all conditions from two knee extensor, one dorsi flexor, and two plantar flexor muscles following TMS to the right leg representation of the left primary motor cortex. A main effect for experimental condition was reported for all three muscle groups. MEP amplitudes were significantly greater in the AOMI condition compared to the BL condition (p = .04) for the knee extensors, AOMI condition compared to the BL condition (p = .03) for the plantar flexors, and AOMI condition compared to the two baseline conditions for the dorsi flexors (ps ≤ .01). The study findings support the notion that changes in CSE are driven by the imagined actions during coordinative AOMI.