How Plantar Exteroceptive Efficiency Modulates Postural and Oculomotor Control: Inter-Individual Variability

Area of Science:

• Neuroscience
• Biomechanics
• Human Physiology

Background:

• Previous research indicated thin plantar inserts enhance postural control and alter vergence in healthy young adults.
• Significant inter-individual variability in response to plantar inserts suggests underlying differences in sensory processing.

Purpose of the Study:

• To investigate the hypothesis that variability in postural control and oculomotor responses to plantar stimulation is due to differing reliance on foot cutaneous afferents.
• To classify subjects based on their reliance on plantar afferents using the Plantar Quotient (PQ) and analyze group differences.

Main Methods:

• Re-analysis of data from 31 healthy young adults who previously participated in an experiment involving plantar inserts.
• Classification of subjects into two groups: Plantar-Independent Subjects (PQ < 100) and Normal Plantar Quotient Subjects (PQ > 100), based on their response to foam surfaces.
• Assessment of postural control and oculomotor (vergence) responses to plantar stimulation in both groups.

Main Results:

• Plantar-Independent Subjects (PQ < 100) showed minimal to no change in postural control and were completely insensitive to plantar stimulation regarding oculomotor control.
• Normal Plantar Quotient Subjects (PQ > 100) exhibited responses consistent with reliance on plantar afferents.
• The degree of plantar reliance, as indicated by PQ, explained the observed inter-individual variability in the initial experiment.

Conclusions:

• Inter-individual variability in postural and oculomotor control related to plantar stimulation is significantly influenced by an individual's reliance on plantar cutaneous afferents.
• Plantar independence may represent a dysfunctional state characterized by inefficient processing of somatosensory information from the feet, potentially due to a latent somatosensory dysfunction.
• This dysfunction, termed Plantar Irritating Stimulus, could impair the central nervous system's ability to utilize foot afferents for balance and vergence, with implications for researchers and clinicians studying foot sole stimulation.