Self-selected conscious strategies do not modulate motor cortical output during action observation

Area of Science:

• Neuroscience
• Motor Control
• Cognitive Psychology

Background:

• The human motor system activates during both action execution and observation, a phenomenon known as the mirror response.
• Factors influencing the mirror response are often studied by manipulating actions or contexts.
• The impact of an observer's intentions and motivation on this response remains largely unexplored.

Purpose of the Study:

• To investigate if observers can consciously control their mirror response by being instructed to either increase or decrease it.
• To explore the role of top-down intentions in modulating motor excitability during action observation.

Main Methods:

• Utilized transcranial magnetic stimulation (TMS) to measure motor-evoked potentials (MEPs) in a thumb abductor muscle.
• Participants (n=13) watched videos of a hand squeezing a rubber ball.
• MEP size, relative to fixation cross observation, served as the index of mirroring. Participants were instructed to observe, then increase, then decrease mirroring.

Main Results:

• No significant differences in MEP facilitation or absolute motor excitability were found across the three experimental blocks (observation, increase, decrease).
• This indicates a lack of conscious control over motor excitability during action observation under the tested conditions.

Conclusions:

• Conscious control over the mirror response appears limited, particularly without a specific, maintained strategy.
• The findings suggest that motor excitability during action observation may be largely automatic and not easily modulated by direct volitional commands.