Processing moving visual scenes during upright stance in elderly patients with mild cognitive impairment.

Background: The ability to maintain balance in an upright stance gradually worsens with age and is even more difficult for patients with cognitive disorders. Cognitive impairment plays a probable role in the worsening of stability. The purpose of this study was to expose subjects with mild cognitive impairment (MCI) and healthy, age-matched controls to moving visual scenes in order to examine their postural adaptation abilities.

Methods: We observed postural responses to moving visual stimulation while subjects stood on a force platform. The visual disturbance was created by interposing a moving picture in four directions (forward, backward, right, and left). The pre-stimulus (a static scene for 10 s), stimulus (a dynamic visual scene for 20 seconds) and post-stimulus (a static scene for 20 seconds) periods were evaluated. We separately analyzed the total path (TP) of the center of pressure (COP) and the root mean square (RMS) of the COP displacement in all four directions.

Results: We found differences in the TP of the COP during the post-stimulus period for all stimulus directions except in motion towards the subject (left  = 0.006, right  = 0.004, and away from the subject  = 0.009). Significant RMS differences between groups were also observed during the post-stimulus period in all directions except when directed towards the subject (left  = 0.002, right  = 0.007, and away from the subject  = 0.014).

Conclusion: Exposing subjects to a moving visual scene induced greater destabilization in MCI subjects compared to healthy elderly controls. Surprisingly, the moving visual scene also induced significant aftereffects in the MCI group. Our findings indicate that the MCI group had diminished adaptation to the dynamic visual scene and recovery. These results suggest that even mild cognitive deficits can impair sensory information integration and alter the sensory re-weighing process.