Effect of artificial gravity on neurocognitive performance during head-down tilt bedrest

Abstract

This study evaluated the acute and chronic effects of intermittent and continuous Artificial Gravity (AG) on cognitive performance during 60 days of Head-down tilt bedrest (HDTBR), a well-established ground-based spaceflight analogue method. Participants were randomly assigned to three groups: intermittent AG, continuous AG, and HDTBR control group without AG exposure. Task performance and electrophysiological measures of attention and working memory were investigated during Simple and Complex tasks in the Visual and the Auditory modality. Compared to baseline, faster reaction time and better accuracy was present during HDTBR regarding the Complex tasks, however, the practice effect was diminished in the three HDTBR groups compared to an ambulatory control group. Brain potentials showed a modality-specific decrease, as P3a was decreased only in the Auditory, while P3b decreased in the Visual modality. No evidence for acute or chronic AG-related cognitive impairments during HDTBR was found.

Fig. 1. Schematic figure of the experiment setup, experiment timeline, and tasks.

a Experiment setup. Participants performed the experimental tasks in a lying position, looking at a computer screen via a cylindrical tube and responses were given using a controller. They wore an EEG cap linked with NIRS optodes throughout performing the experimental tasks. b Schematic figure of the experiment timeline and the HDTBR Phases regarding the HDTBR groups. AMBCtrl group had the same timeline without undergoing HDTBR and AG. c Stimulus presentation in the Visual tasks. Participants had to indicate whether two successively presented lines (Reference and Probe stimuli) had the same orientation or not. Twenty percent of the Probe stimuli were replaced by a task-irrelevant picture (Irrelevant stimulus). d Stimulus presentation in the Auditory tasks. Participants had to indicate whether two successively presented sound beeps (Reference and Probe stimuli) had the same pitch or not. Twenty percent of the Probe stimuli were replaced by task-irrelevant environmental noises (Irrelevant stimulus).

Fig. 2. Behavioral task performance in the three HDTBR experimental groups (iAG, cAG and ctrlAG averaged together).

a RT in the HDTBR groups (iAG, cAG and ctrlAG averaged together) comparing the three Phases (BDC, HDT and R). Regarding Simple tasks, a significant RT change was only present in the Auditory modality between the indicated Phases, while for the Complex tasks, a significant difference was found in both the Visual and the Auditory modality between the indicated Phases. b Accuracy in the HDTBR groups (iAG, cAG and ctrlAG averaged together) comparing the three Phases (BDC, HDT and R). The Simple and the Complex tasks are shown separately. A significant difference in Accuracy was only present in the Auditory modality and was limited to the Complex task between the indicated Phases. Error bars represent standard deviation (SD). *p < 0.05; **p < 0.01.

Fig. 3. The practice effect in RT was estimated by a linear model fitted on all 9 sessions.

The linear function equation was y = mx + b, (where y is the RT, x is the session number, and m is the slope of the RT), which was calculated separately for all four tasks for the HDTBR experimental groups (iAG, cAG, and ctrlAG averaged together) and for the AMBCtrl group. a Simple tasks, with increased RT in the HDTBR and decreased RT in the AMBCtrl in both Modalities. b A decreasing trend in the Complex tasks in both Modalities for the HDTBR and the AMBCtrl.

Fig. 4. Amplitudes of ERP components (P3a and P3b) in the HDTBR experimental groups (iAG, cAG and ctrlAG averaged together).

Complex tasks are analyzed in both modalities. a P3a amplitude (Irrelevant stimuli) in the HDTBR groups comparing the three Phases (BDC, HDT and R). b P3b amplitude (Target stimuli) in the HDTBR groups comparing the three Phases (BDC, HDT and R). Error bars represent standard deviation (SD). *p < 0.05; **p < 0.01.