Cortical responses to balance perturbations persist without active postural control.

Area of Science:

• Neuroscience
• Biomechanics
• Human Motor Control

Background:

• Standing balance involves complex neural processing, including rapid reflexes and longer-latency cortical activity.
• Electroencephalography (EEG) studies identify balance N1 and midfrontal theta power as markers of cortical activity during postural disturbances.
• The precise role of these cortical markers in active postural control versus general sensory event detection remains unclear.

Purpose of the Study:

• To determine if balance N1 and midfrontal theta responses depend on active postural control or reflect general sensory processing.
• To dissociate the neural processing of balance perturbations from the motor execution of corrective actions.

Main Methods:

• Participants underwent identical support-surface perturbations in a robotic balance simulator.
• Cortical (EEG) and muscle activity were measured during active balancing and passive motion conditions.
• Sensory feedback (whole-body vs. footplate-only) and motor engagement (isometric contraction vs. relaxed) were systematically manipulated.

Main Results:

• Balance N1 and midfrontal theta responses persisted with only modest amplitude reductions during passive motion, despite significant reductions in muscle activity.
• Cortical responses remained even in relaxed postures with minimal muscle engagement and altered sensory feedback.
• Muscle responses were markedly suppressed in passive and relaxed conditions, while cortical markers showed persistence.

Conclusions:

• Balance N1 and midfrontal theta are not dependent on active postural control.
• These cortical markers index the early detection and evaluation of unexpected sensory events, rather than the generation of corrective actions.
• Findings suggest a role in prediction error or surprise processing during postural disturbances.