Effect of head position on postural orientation and equilibrium

Area of Science:

• Neuroscience
• Biomechanics
• Motor Control

Background:

• Head position is crucial for maintaining postural stability in many species.
• Understanding how the head influences postural control is vital for diagnosing and treating balance disorders.

Purpose of the Study:

• To investigate the impact of altered head positions on postural orientation during quiet stance.
• To determine if head position changes affect the rapid postural response to support surface translations.

Main Methods:

• Cats were trained to stand in various head positions (center, left, right, up, down) on a movable platform.
• Support surface translations in 16 directions perturbed stance, with responses quantified via ground reaction forces, kinematics, dynamics, center of mass trajectory, and electromyographic (EMG) activity.
• Analysis included tonic and evoked EMG responses in limb and trunk muscles, as well as joint torques.

Main Results:

• Significant changes in head position involved neck, scapular, and trunk rotation.
• Tonic electromyographic (EMG) levels were modulated in forelimb and scapular muscles, but not hindlimb muscles.
• Despite large head orientation changes, postural equilibrium was maintained during translations; body center of mass trajectory was consistent.
• Forelimb joint torques showed the most significant changes.
• Evoked EMG responses in forelimb and scapular muscles varied in magnitude but not spatial tuning; hindlimb responses were unaffected.

Conclusions:

• The spatial and temporal patterns of automatic postural responses are robust to changes in head position.
• Modulation of evoked activity amplitudes, rather than pattern changes, is the primary adjustment to altered head orientation.
• These findings highlight the adaptability of the feline postural control system.