Attentional focus and imagery vividness facilitate corticospinal excitability during contralateral action observation and motor imagery

Action Observation (AO) and Motor Imagery (MI) are widely used techniques in motor simulation research and are applied in motor skill learning and rehabilitation. The Dual-Action Simulation Hypothesis (DASH) suggests that AO and MI function independently, while the Visual Guidance Hypothesis (VGH) proposes that AO supports MI, where MI acts as the primary driver of corticospinal excitability (CSE) facilitation. In this study, we examined the individual and interactive effects of AO and MI on CSE facilitation. Furthermore, we examined self-reported perceptions of attentional focus and imagery vividness, potential factors often neglected in this context. Twenty-one right-handed participants received single-pulse Transcranial Magnetic Stimulation (TMS) while observing hand actions performed with the contralateral or ipsilateral hand while simultaneously imagining the same or the opposite hand movement. This manipulation dissociated laterality (contralateral vs ipsilateral) from action-imagery congruency, yielding congruent pairings (same hand for AO and MI) and coordinative pairings (different hands for AO and MI). Motor-evoked potentials (MEPs) were recorded from the first dorsal interosseous (FDI) muscle contralateral to the stimulated hemisphere and normalised across participants. Results indicated that AO and MI alone did not elicit CSE facilitation. However, individuals reporting greater attentional focus exhibited significantly greater facilitation during contralateral AO. Similarly, reported scores of vivid motor imagery predicted stronger CSE responses during contralateral MI but not ipsilateral. These findings suggest that CSE during concurrent AO and MI may depend less on the specific combination of observed and imagined actions and more on engagement-related factors such as attentional focus and imagery vividness.