Fingertip-Coupled Spindle Signaling Does Not Contribute to Reduce Postural Sway Under Light Touch

Area of Science:

• Human sensorimotor control
• Biomechanics
• Neuroscience

Background:

• Light touch (LT) is known to improve postural stability, but the underlying sensory mechanisms are not fully understood.
• Muscle afferents from the touching fingertip are hypothesized to contribute significantly to this postural control.
• Investigating the role of muscle afferents is crucial for understanding sensory integration in balance.

Purpose of the Study:

• To determine the specific contribution of muscle afferents from the fingertip to postural sway reduction during light touch.
• To test the hypothesis that removing muscle afferent feedback would increase postural sway.
• To elucidate the sensory feedback pathways involved in light touch-mediated postural control.

Main Methods:

• Eleven participants stood with eyes closed on an unstable surface, performing postural sway measurements.
• Experimental conditions included light touch with partial muscle afferents (PMA) and no muscle afferents (NMA).
• A no-touch (NT) condition served as the control, with center of pressure displacement recorded in anteroposterior (AP) and mediolateral (ML) axes.

Main Results:

• Light touch (LT) significantly decreased all measured postural sway quantifiers compared to the no-touch (NT) condition.
• Withdrawal of muscle afferent information (NMA) did not increase postural sway.
• A statistically significant decrease in AP center of pressure variability was observed in the NMA condition, contrary to the hypothesis.

Conclusions:

• Muscle afferent input from the fingertip may not contribute to, or could even impair, sensory feedback for postural control during light touch.
• Non-spindle fingertip afferents appear to provide the primary sensory feedback during light touch of a stable surface for quiet standing.
• These findings challenge traditional views on the role of muscle afferents in tactile-mediated postural adjustments.