Can prepared anticipatory postural adjustments be updated by proprioception?

Area of Science:

• Neuroscience
• Biomechanics
• Motor Control

Background:

• Anticipatory postural adjustments (APAs) are crucial for obstacle negotiation, involving center of pressure (CoP) shifts before stepping.
• Sensory information's role in APAs is established, but online modification of feedforward commands remains unclear.

Purpose of the Study:

• To investigate how the central nervous system (CNS) modulates APAs in response to altered proprioceptive input before or during stepping initiation.
• To determine if sensory information can be used online to adjust the feedforward command of APAs.

Main Methods:

• Subjects stepped over obstacles with eyes closed, synchronized to a tone.
• Ankle muscle vibration was used to modify proprioceptive inflow, applied either during APA initiation or before APA onset.
• Postural reactions and subsequent step thrust amplitude were analyzed.

Main Results:

• Vibration during APA initiation minimally affected early APAs, except for cutaneous stimulation, suggesting reduced reliance on proprioception.
• Only the final CoP adjustment incorporated biased proprioceptive information.
• Pre-APA vibration induced a postural reaction, and subsequent stepping adjusted thrust amplitude accordingly.

Conclusions:

• The CNS can update planned motor commands for APAs online before they are triggered.
• Proprioceptive feedback plays a role in the later stages of APA execution and can influence subsequent motor planning.