Influence of central set on human postural responses.

Area of Science:

• Human motor control
• Neuroscience
• Biomechanics

Background:

• Automatic postural responses are crucial for maintaining balance.
• Central set, influenced by prior experience, can modulate these responses.
• Understanding central set's role is key to explaining adaptive postural control.

Purpose of the Study:

• To investigate how central set affects automatic postural responses to support-surface perturbations.
• To examine the influence of prior experience with stimulus velocity and amplitude on postural control.
• To analyze electromyograph (EMG) and torque responses under varying central set conditions.

Main Methods:

• Subjects experienced horizontal support-surface perturbations with varied stimulus velocities and amplitudes under serial, random, expected, unexpected, practiced, and unpracticed conditions.
• Measured leg and trunk electromyograph (EMG) activations and associated ankle torque responses.
• Analyzed the pattern and magnitude of these responses in relation to central set variations.

Main Results:

• Randomizing perturbation amplitudes eliminated the scaling of initial electromyograph (EMG) and torque responses, indicating central set to anticipated amplitudes.
• Expectation of stimulus amplitude significantly affected initial torque responses (over- or under-responding).
• Unexpected stimulus velocities led to consistent over-responses, suggesting a difference in encoding velocity versus amplitude information.

Conclusions:

• Central set, particularly expectation of amplitude, plays a significant role in modulating the magnitude of automatic postural responses.
• Late antagonist muscle activation (tibialis) can partially correct initial response errors.
• Two distinct neural mechanisms likely underlie the adaptive effects of central set on postural control.