Effects of simulated microgravity on human emotion processing and startle reflex habituation

The aim of the present study was to investigate the influences of simulated microgravity on psychophysiological responses to emotional pictures. For this purpose, we selected a sample of 22 male subjects with characteristics similar to those of an astronaut. A group of 11 males submitted to simulated microgravity (BR; 4-hours head-down bed rest) were compared with a matched group of 11 sitting controls. The experimental session consisted of passive viewing of 75 affective pictures, divided in three emotional categories: pleasant, neutral and unpleasant. Slides were randomly presented for 6 seconds. During picture viewing, startle reflex, pre-pulse inhibition (PPI), and evoked potentials from three scalp sites (Pz, F7, and F8) were recorded. Results showed an impaired startle reflex habituation in BR subjects compared to controls. The PPI task, which reflects orienting of attention towards primary stimulus, showed in BR a reduced elaboration of unpleasant stimuli compared to pleasant stimuli. Furthermore, evoked potentials showed specific cortical inhibition to arousing emotional pictures in BR subjects compared to controls, this occurred at both, intermediate component (P300) and late positive complex (SPW). Results point to an impairment of emotional processing in humans under microgravity condition. This altered perception could threaten the success of spatial missions, for instance in case of impaired capability of astronauts to adequately perceive an emergency situation.