Do we use a priori knowledge of gravity when making elbow rotations?

Area of Science:

• * Neuroscience
• * Motor Control
• * Biomechanics

Background:

• * Understanding how the brain adapts motor commands to changing environmental conditions, such as gravity, is crucial for motor control research.
• * Previous studies suggest rapid adaptation to altered sensory feedback, but the role of prior knowledge of gravity in movement planning remains unclear.

Purpose of the Study:

• * To investigate if motor commands are customized for movement orientation relative to gravity from the first trial.
• * To determine if participants utilize a priori knowledge of gravity during movement planning when changing body orientation.

Main Methods:

• * Participants performed fast elbow flexions and extensions in the transverse plane.
• * Movements practiced in reclined orientations (with or against gravity) were compared to those in upright orientation.
• * Analysis focused on the first trial in the new orientation and later trials after familiarization.

Main Results:

• * A decrease in peak angular velocity and movement amplitude was observed in the first trials after changing body orientation.
• * These initial decrements disappeared after a 30-trial familiarization block in the upright position.
• * The observed effects were consistent regardless of whether prior movements were with or against gravity.

Conclusions:

• * Motor command customization for gravity is not immediate upon changing body orientation.
• * Participants employed a general motor strategy, likely due to unreliable or limited information about external conditions.
• * A priori knowledge of gravity was not specifically used to customize motor commands for neutral gravity conditions.