Selective facilitation of short latency postural reflexes by instability

Area of Science:

• Neuroscience
• Biomechanics
• Human Physiology

Background:

• Postural reflexes are vital for maintaining balance.
• The neural mechanisms underlying reflex modulation during instability are not fully understood.

Purpose of the Study:

• To investigate if leaning-induced instability enhances postural reflexes.
• To identify the neural level mediating these reflex enhancements.

Main Methods:

• Healthy participants adopted leaning postures to induce instability.
• Recordings of muscle activity (postural, eye, neck) and cerebellar responses were taken during stable stance and leaning.
• Trunk and mastoid perturbations were applied to assess reflex responses.

Main Results:

• Short-latency reflexes in the soleus muscle were enhanced during forward lean.
• Cerebellar responses to trunk stimuli were larger during anterior lean.
• Reflexes in leg muscles were generally larger during leaning compared to upright stance.

Conclusions:

• Instability enhances axially-evoked postural reflexes in specific leg muscles (soleus), but not others (tibialis anterior).
• These enhancements are likely mediated by modulation of descending brainstem pathways.