Somatosensory loss increases vestibulospinal sensitivity.

Area of Science:

• Neuroscience
• Biomechanics
• Human Physiology

Background:

• Diabetic peripheral neuropathy (PNP) causes somatosensory loss, potentially impacting balance control.
• The vestibular system's role in postural stability is well-established, but its compensatory function in sensory loss is less understood.

Purpose of the Study:

• To investigate if somatosensory loss in diabetic peripheral neuropathy leads to increased sensitivity to vestibular stimulation.
• To compare the postural responses to galvanic vestibular stimulation (GVS) in individuals with and without PNP, under normal and unstable surface conditions.

Main Methods:

• Bipolar galvanic stimulation (GVS) was applied at varying intensities to subjects with and without PNP.
• Postural lean was measured using center of foot pressure (CoP) displacement while subjects stood with eyes closed on stable and compliant foam surfaces.
• Trunk segment movement and center of mass (CoM) angle were analyzed to understand postural control strategies.

Main Results:

• Subjects with PNP demonstrated significantly greater forward CoP displacement in response to GVS compared to controls, indicating heightened vestibular sensitivity.
• This increased sensitivity was more pronounced at higher GVS intensities and when standing on an unstable surface.
• GVS had a greater effect on trunk orientation than on CoM angle, suggesting vestibular control of trunk posture.

Conclusions:

• The study provides evidence for increased vestibular system sensitivity in individuals with peripheral neuropathy, acting as a compensatory mechanism for disrupted somatosensory input.
• Altered vestibular gain, potentially increased central vestibular gain compensating for decreased peripheral somatosensory gain, may underlie these findings.
• The vestibular system appears to prioritize trunk orientation control for maintaining posture, especially when other sensory information is unreliable.