The influence of having the eyelids open or closed on undisturbed postural control

To assess the possible interactions between the physiological mechanisms involved in eyelid closure and stance maintenance, 20 healthy adults were required to keep their eyes open in the dark (EOd), in daylight (EO), or to close them normally (EC), respectively and in random order. The analysis was focused on elementary motions computed from the complex centre of pressure (CP) trajectories, that is to say the vertical projection of the centre of gravity (CGv) and the difference between CP and CGv (CP-CGv). The results indicate that the mean amplitudes of the CP-CGv spectra are statistically reduced in EOd when compared to the EC condition. This diminution is thought to express a decrease in the level of activity of lower limb muscles involved in stance control. Interestingly, the CNS does not really seem to gain from these reduced horizontal accelerations at the CG level since the CGv amplitudes are in turn only slightly reduced. It can thus be hypothesised that, despite the fact that visual information in the EOd condition remains unavailable, the somesthetic cues continue to play a minor role in the detection-correction process aimed at controlling undisturbed stance.