Retention of cross-coupled illusion training to allow for a shorter radius space centrifuge

During space exploration missions, prolonged exposure to microgravity causes physiological deconditioning in astronauts. Artificial gravity (AG) through centrifugation has the potential be a comprehensive countermeasure to this deconditioning. However, a fast spinning environment causes the Coriolis cross-coupled (CC) illusion when head tilts are made, which is disorienting and leads to motion sickness. To reduce the spin rate, a much larger centrifuge is required to produce a desired gravitational level. Previous research has shown humans can be adapted to the CC illusion, such that higher spin rates become tolerable with training. However, it remains unclear if this adaptation can be retained for an extended period of time (e.g., If the training occurs pre-flight, how much is retained by the time astronauts are centrifuged in transit?). In the current study, we investigated CC illusion training retention by retesting subjects after 30 days since the conclusion of their original 10-day training. We compared the level of adaptation (i.e., the spin rate at which the CC illusion was just barely sub-threshold) in three days of retention tests to their level at the end of the original 10-day training and to the first three days of original training in a control group (never experienced any prior training). Preliminary results suggest that a substantial portion of the original adaptation was retained, even after this extended layoff. The CC illusion threshold was lower in some subjects after 30 days off compared to that individual's threshold at the end of the 10-day training period; however, it was typically higher than pretraining thresholds, suggesting some level of retention. Furthermore, across three consecutive days of retraining, some subjects tended to increase their CC illusion threshold much more quickly than during the first three days of the original training. This retained training may make AG a more feasible countermeasure for spaceflight-induced physiological deconditioning, enhancing human space exploration capabilities.