Rapid online selection between multiple motor plans.

Area of Science:

• Neuroscience
• Motor Control
• Human Movement Science

Background:

• Voluntary movement theories suggest precomputation of multiple motor strategies.
• Online decisional processing during movement execution remains an area of active research.

Purpose of the Study:

• To investigate rapid decisional processing and motor strategy selection during human reaching movements.
• To examine the timing and nature of corrective responses to perturbations and goal changes.

Main Methods:

• Participants performed reaching movements with obstacles and experienced unexpected mechanical perturbations.
• Electromyography measured muscle stretch responses during different movement epochs.
• Experiments manipulated obstacle proximity and the number of potential movement targets.

Main Results:

• Two distinct motor strategies were observed when a perturbation directed the limb toward an obstacle, with muscle response differences emerging within 60 ms (R2 epoch).
• The choice between strategies correlated with the estimated limb position at the time of perturbation.
• Movement redirection to alternative targets after perturbation showed distinct muscle responses around 75 ms (R3 epoch).

Conclusions:

• Decisional processes are rapidly integrated into ongoing movement execution.
• A hierarchical control structure is suggested, with R2 epoch responses related to 'how' to achieve a goal and R3 epoch responses related to 'what' goal to pursue.