The effects of simulated microgravity on characteristics of slow presaccadic potentials

The parameters of saccades and presaccadic slow potentials were studied in seven right-handed male volunteers with a dominant right eye before and after exposure to 6-day dry immersion. Visual stimuli were presented using three light diodes, which were located in the center of the visual field (the central fixation stimulus) and 10° to the right and left of it (peripheral stimuli (PSs)). The subjects performed a test with simple saccades to a PS and a test with antisaccades to the point located symmetrically in the opposite visual field. The EEG (19 monopolar leads) and electrooculogram were recorded. To isolate slow potentials, backward EEG averaging was performed, with the moment of switching on the PS serving as a trigger for the averaging. It was found that the characteristics of saccadic eye movements did not substantially change after exposure to immersion. However, both tests revealed a change in topography and a decrease in the amplitude of presaccadic slow negative potentials (PSNPs) during immersion. Characteristically, the focus of presaccadic negativity shifted to the right hemisphere so that the PSNP amplitude sharply decreased in the left and increased in the right hemisphere. A significant decrease in the PSNP amplitude on day 6 of immersion was found in the midline and left-hemispheric frontal and parietal leads. It may be suggested that, because of support unloading and a decrease in proprioceptive input, exposure to microgravity causes a decrease in the activity of the left hemisphere and prefrontal and parietal cortices, initially involved in preparation and realization of motor responses. The activation of the right hemisphere could be of compensatory character.