Continuous and Intermittent Artificial Gravity as a Countermeasure to the Cognitive Effects of 60 Days of Head-Down Tilt Bed Rest

Abstract

Environmental and psychological stressors can adversely affect astronaut cognitive performance in space. This study used a 6° head-down tilt bed rest (HDBR) paradigm to simulate some of the physiologic changes induced by microgravity. Twenty-four participants (mean ± SD age 33.3 ± 9.2 years, N = 16 men) spent 60 consecutive days in strict HDBR. They were studied in three groups of eight subjects each. One group served as Control, whereas the other two groups received either a continuous or intermittent artificial gravity (AG) countermeasure of 30 min centrifugation daily (1 g acceleration at the center of mass and 2 g at the feet). Participants performed all 10 tests of NASA's Cognition battery and a brief alertness and mood survey repeatedly before, during, and after the HDBR period. Test scores were adjusted for practice and stimulus set difficulty effects. A modest but statistically significant slowing across a range of cognitive domains was found in all three groups during HDBR compared to baseline, most consistently for sensorimotor speed, whereas accuracy was unaffected. These changes were observed early during HDBR and did not further worsen or improve with increasing time in HDBR, except for emotion recognition performance. With increasing time spent in HDBR, participants required longer time to decide which facial emotion was expressed. They were also more likely to select categories with negative valence over categories with neutral or positive valence. Except for workload, which was rated lower in the Control group, continuous or intermittent AG did not modify the effect of HDBR on cognitive performance or subjective responses. Participants expressed several negative survey responses during HDBR relative to baseline, and some of the responses further deteriorated during recovery, which highlights the importance of adequate medical and psychological support during extended duration HDBR studies. In conclusion, 60 days of HDBR were associated with moderate cognitive slowing and changes in emotion recognition performance, but these effects were not mitigated by either continuous or intermittent exposure to AG for 30 min daily.

Keywords: bed rest; cognition; emotion recognition; microgravity; performance; spaceflight.

Figure 1

Cognitive speed, accuracy, and efficiency across cognitive domains relative to the 60-day head-down tilt (HDT) bed rest period (gray background) for the Control group (black circles), continuous artificial gravity group (cAG; white squares), and intermittent artificial gravity group (iAG; white triangles). Estimates reflect unadjusted means z-transformed based on baseline (pre-HDT) performance within each of the 10 Cognition tests and then averaged across tests. To reflect the analytical approach (adjusting for baseline performance), means were shifted within groups to reflect a pre-HDT baseline performance of 0 (zero).

Figure 2

Change in cognitive performance in the head-down tilt (HDT) bed rest period relative to pre-HDT baseline. Estimates reflect z-scores based on the mean and SD of pre-HDT baseline performance. Error bars reflect unadjusted 95% confidence intervals. (A) Estimates for the Control group (black circles), cAG group (white squares), and iAG group (white triangles); (B) Estimates for the difference cAG-Control (squares) and iAG-Control (triangles); ^*adjusted p < 0.05; ^**adjusted p < 0.01; ^***adjusted p < 0.001; MP, Motor Praxis; VOLT, Visual Object Learning Test; F2B, Fractal 2-Back; AM, Abstract Matching; LOT, Line Orientation Test; ERT, Emotion Recognition Test; MRT, Matrix Reasoning Test; DSST, Digit Symbol Substitution Test; BART, Balloon Analog Risk Test; PVT, Psychomotor Vigilance Test; ALL, scores averaged across cognitive domains.

Figure 3

Change in survey responses during head-down tilt (HDT) bed rest (A) and post-HDT recovery (B) relative to pre-HDT baseline for the Control group (black circles), cAG group (white squares), and iAG group (white triangles). Estimates reflect points on an 11-point scale. For each variable, the negative response anchor is shown (e.g., “unhappy” and “very sleepy”). Positive scores reflect more negative assessments relative to baseline (graphs on the left) or control (graphs on the right). Error bars reflect unadjusted 95% confidence intervals. ^*adjusted p < 0.05; ^**adjusted p < 0.01; ^***adjusted p < 0.001; ^****adjusted p < 0.0001.

Figure 4

Speed and accuracy on the Emotion Recognition Test (ERT) relative to the 60-day HDT bed rest period (gray background) for the control group (black circles), cAG group (white squares), and iAG group (white triangles). Estimates reflect unadjusted means (SEs) z-transformed based on baseline (pre-HDT) performance. To reflect the analytical approach (adjusting for baseline performance), means were shifted within groups to reflect a pre-HDT baseline performance of 0 (zero).

Figure 5

Change in cognitive performance in post-HDT recovery period relative to pre-HDT baseline. Estimates reflect z-scores based on the mean and SD of pre-HDT baseline performance. Error bars reflect unadjusted 95% confidence intervals. (A) Estimates for the Control group (black circles), cAG group (white squares), and iAG group (white triangles); (B) Estimates for the difference cAG-Control (white squares) and iAG-Control (white triangles); ^*adjusted p < 0.05; ^**adjusted p < 0.01; MP, Motor Praxis; VOLT, Visual Object Learning Test; F2B, Fractal 2-Back; AM, Abstract Matching; LOT, Line Orientation Test; ERT, Emotion Recognition Test; MRT, Matrix Reasoning Test; DSST, Digit Symbol Substitution Test; BART, Balloon Analog Risk Test; PVT, Psychomotor Vigilance Test; ALL, scores averaged across cognitive domains.