When one sensory input becomes unreliable (for example, eyes closed on a moving platform), which of the following best describes the CNS response?

• A. The CNS downweights the unreliable input and upweights reliable inputs (vision, proprioception, vestibular) to maintain balance, altering sway patterns.
• B. The CNS stops processing sensory information.
• C. The CNS ignores all inputs and relies on random movement.
• D. The CNS upweights the unreliable input to test stability.

Answer: (A)

When balance is threatened by a unreliable input, the brain adjusts by reweighting sensory information to rely more on cues that remain trustworthy. In this scenario, vision is unavailable because the eyes are closed, and the moving platform disrupts the reliability of proprioceptive feedback from the feet. The CNS therefore downplays the unreliable input (vision) and increases reliance on the remaining reliable sources, especially vestibular information about head motion and orientation, to stabilize posture. This reweighting shifts how sway is produced, typically changing sway amplitude and timing as the system depends more on vestibular cues to maintain the center of mass over the base of support.