Large Postural Sways Prevent Foot Tactile Information From Fading: Neurophysiological Evidence

Area of Science:

• Neuroscience
• Biomechanics
• Human Motor Control

Background:

• Cutaneous foot receptors are crucial for maintaining balance during quiet standing.
• Receptor activation is influenced by the speed and amplitude of postural oscillations.
• Prolonged small postural sways may lead to receptor adaptation and reduced sensory transmission.

Purpose of the Study:

• To investigate the hypothesis that cutaneous input transmission to the cortex is reduced during prolonged small postural sways.
• To explore central mechanisms that might trigger larger postural sways to reactivate adapted receptors.
• To compare somatosensory cortical potentials during small versus large postural sways.

Main Methods:

• 16 young adults stood with eyes closed, undergoing electrical stimulation of the foot sole.
• Somatosensory cortical potentials (P50N90 amplitudes) were measured during small and large postural sways.
• Cortical source analyses examined brain activity during specific pre-sway intervals.

Main Results:

• P50N90 amplitudes were significantly greater during large sways than small sways, indicating increased cutaneous transmission.
• Preceding large sways, postural oscillations had smaller amplitudes, suggesting sustained foot sole compression.
• Cortical source analysis showed decreased somatosensory cortex activity and increased motor planning area activity before large sways.

Conclusions:

• Large postural sways during quiet standing are a functional behavior to release skin compression and reactivate mechanoreceptors.
• These self-generated motor commands create sensory reafference that aids in controlling postural sway.
• The findings highlight the dynamic interplay between sensory adaptation and motor control in maintaining balance.