Startle evokes nearly identical movements in multi-jointed, two-dimensional reaching tasks

Area of Science:

• Neuroscience
• Motor Control
• Biomechanics

Background:

• StartReact, the involuntary release of planned movements by the startle reflex, is well-documented in simple tasks.
• Previous research indicated no kinematic or muscle activation differences between StartReact and voluntary movements in single-joint actions.
• The robustness and equivalence of StartReact in complex multi-joint movements remained largely unevaluated.

Purpose of the Study:

• To investigate if StartReact evokes accurate and precise multi-joint reaching movements in an unrestricted, multi-directional workspace.
• To compare movement kinematics and muscle activation patterns of StartReact with voluntary movements during multi-joint reaching.
• To determine the robustness and equivalence of StartReact in tasks with multiple degrees of freedom.

Main Methods:

• Participants performed multi-joint reaching movements in a multi-directional workspace.
• Loud acoustic stimuli were presented to evoke StartReact responses.
• Movement kinematics and muscle activation patterns were recorded and analyzed for both StartReact and voluntary movements.

Main Results:

• StartReact movements were successfully evoked in all tested directions.
• Muscle activation occurred stereotypically earlier in StartReact responses.
• Despite earlier activation, the relative timing of agonist/antagonist muscle firing pairs remained similar between StartReact and voluntary movements.
• Movement accuracy and precision were comparable between StartReact and voluntary multi-joint reaching.

Conclusions:

• StartReact is a robust phenomenon present and equivalent in multi-joint reaching tasks.
• The findings support the potential clinical utility of StartReact for assessing both healthy and impaired motor control.
• StartReact provides a reliable method to study involuntary movement release mechanisms in complex actions.