Short Duration Simulated Microgravity Models Improve Executive Function

Abstract

PURPOSE: To determine whether executive function is altered during two variations of simulated microgravity head down tilt protocols. METHODS: 26 healthy volunteers (n=19 females and 7 males; 20.0 ± 1.7 years; 165.6 ± 24.5 cm; 71.1 ± 15.9 kg; mean±SD) took part in two randomly assigned separate simulated microgravity sessions consisting of 1.5 hours at -6° head down tilt (HDT) sessions. Each testing session lasted approximately 2.5 hours. One session consisted of the broadly used -6° HDT facing up (HDT-FU), while the other consisted of a -6° HDT facing down (HDT-FD) modification of the standard method. For each condition, the participant completed a computerized Stroop Color and Word Test during a thirty-minute horizontal position (0° tilt) prior to the interventions and again prior to the end of the 1.5-hour HDT protocols. The Stroop Color and Word Test consisted of 3 tasks (60 trials per task) including: 1) a Naming task, 2) an Inhibition task, and 3) an Inhibition/Switching task. To minimize the learning effect, both the HDT-FU and HDT-FD sessions were counterbalanced amongst all participants and were separated by a minimum of 48 hours. RESULTS: Our cognitive reaction time results demonstrate a main effect of time (pre HDT 777.60 ± 18.08ms vs post HDT 749.30 ± 19.11ms, p<0.01) and a main effect of Stroop Test (Naming < Inhibition < Inhibition/Switching, p<0.01). Additionally, we observed that the 1.5-hour protocol selectively improved the Inhibition/Switching reaction times (the most executive component) for both the HDT-FU (pre HDT-FU 945.68 ± 32.87ms vs post HDT-FU 903.16 ± 33.78ms, p=0.02) and HDT-FD (pre HDT-FD 961.25 ± 38.55ms vs post HDT-FD 868.91 ± 30.40ms, p<0.01). CONCLUSION: When executive demand is increased under short-term simulated microgravity head down tilt conditions, regardless of the position (face up or face down), cognitive reaction time is decreased, suggesting an improvement in overall cognitive function.