Effects of 45 Days -6°Head-down Bed Rest on Males' Frontal Alpha Asymmetry and Emotion

Suffering from the anxiety and depression under spaceflight may impair astronauts' cognitive performance. It is difficult to investigate human emotion changes in real space environment. Previous studies suggested that the head-down bed rest(HDBR) which simulated weightlessness environment was used to evaluate emotion changes with self-reported scales and turned out to be useful tools. In addition, scientific research suggests that emotional responses are composed of initial emotional reactivity and ongoing emotion regulation. However, it is still uncertain that whether the emotion regulation competence will be impaired or not under HDBR. Therefore, we investigated the effects of 45 day-6° HDBR on participants' self-reported anxiety and depression as well as the frontal EEG asymmetry which represents their emotion regulation competence.Sixteen healthy non-smoking young men whose mean age was 26.33 years old(SD = 4.13) were recruited in the experiment. The participants had no history of chronic or acute diseases and normal vision. They were right-handed, non-athletes and none of them were allowed to use medication, tobacco, or caffeine-containing drinks during the experiment. They should keep lying in the bed with-6 degree for 45 days. EEG data and Beck Anxiety Inventory(BAI) as well as the Beck Depression Inventory(BDI) were assessed and analyzed on two days before HDBR, 11 th, 20 th, 32 nd and 40 th day under HDBR together with the 8th day after HDBR respectively. According to the previous studies, we mainly measured EEG alpha asymmetry in the frontal area(FP1, FP2, F3 and F4) and the EEG was referenced on-line to the left mastoid and re-referenced off-line to the Cz electrode. Throughout the EEG recording, the impedance of the electrodes was maintained under 5 k?. The electroencephalogram(EEG) was recorded by 40 Ag/AgCl electrodes mounted on a custom-made cap according to the extended 10-20 system and continuously sampled at 1000 Hz by a Neuroscan NuAmps amplifier. The band-pass filter range of 0.01 to 200 Hz was used during the EEG recording. The artifact-free EEG was analyzed with Discrete Fourier Transforms(DFT) which use a Hanning window of one second width and 5% overlap. Power was extracted from the 8~13 Hz frequency band and measured with mean square microvolt as its unit. The raw data of power was then transformed in the natural log(ln) in order to normalize the data distribution.The value of the frontal EEG asymmetry was calculated by subtracting the value of the left EEG power from the value of the right EEG power. Statistic analyses were performed using two-way [Time points(pre-HDBR, HDBR11, HDBR20, HDBR32, HDBR40 and post-HDBR) × electrode sites algorithm(lnFP2-lnFP1 vs. lnF4-lnF3)] repeated-measures ANOVAs with SPSS 13.0 Software. Statistically significant differences were assessed at 0.05 level and power of the effect was assessed with partial eta-squared(η2) and the correction was done by Greenhouse-Geisser coefficient. Frontal EEG asymmetry was clear to perform a linear increase curve(F(5, 75) = 2.91, p = 0.019, η2 = 0.16) across all six time points. The main effect of electrode sites algorithm was not significant(F(1, 15) = 0.03, p = 0.855, η2 0.001), and there was no significant interaction between time points and electrode sites algorithm(F(5, 75) = 0.45, p = 0.813, η2 = 0.03), either. The self-reported anxiety(F(5, 75) = 2.09, p = 0.076; η2 = 0.12) and depression(F(5, 75) = 0.55, p = 0.738; η2 = 0.04) showed no significant changes before, during and after the HDBR. These results indicate that under extreme environment, people who prefer to maintain the stability of their emotional state paid many efforts to regulate their negative emotions. Only in this way can they reported stable anxiety and depression feelings. Above all, their anxiety and depression symptoms did not fluctuate significantly under simulated weightlessness environment.