The Effects of 30 Minutes of Artificial Gravity on Cognitive and Sensorimotor Performance in a Spaceflight Analog Environment

Abstract

The altered vestibular signaling and somatosensory unloading of microgravity result in sensory reweighting and adaptation to conflicting sensory inputs. Aftereffects of these adaptive changes are evident postflight as impairments in behaviors such as balance and gait. Microgravity also induces fluid shifts toward the head and an upward shift of the brain within the skull; these changes are well-replicated in strict head-down tilt bed rest (HDBR), a spaceflight analog environment. Artificial gravity (AG) is a potential countermeasure to mitigate these effects of microgravity. A previous study demonstrated that intermittent (six, 5-mins bouts per day) daily AG sessions were more efficacious at counteracting orthostatic intolerance in a 5 day HDBR study than continuous daily AG. Here we examined whether intermittent daily AG was also more effective than continuous dosing for mitigating brain and behavioral changes in response to 60 days of HDBR. Participants (n = 24) were split evenly between three groups. The first received 30 mins of continuous AG daily (cAG). The second received 30 mins of intermittent AG daily (6 bouts of 5 mins; iAG). The third received no AG (Ctrl). We collected a broad range of sensorimotor, cognitive, and brain structural and functional assessments before, during, and after the 60 days of HDBR. We observed no significant differences between the three groups in terms of HDBR-associated changes in cognition, balance, and functional mobility. Interestingly, the intermittent AG group reported less severe motion sickness symptoms than the continuous group during centrifugation; iAG motion sickness levels were not elevated above those of controls who did not undergo AG. They also had a shorter duration of post-AG illusory motion than cAG. Moreover, the two AG groups performed the paced auditory serial addition test weekly while undergoing AG; their performance was more accurate than that of controls, who performed the test while in HDBR. Although AG did not counteract HDBR-induced gait and balance declines, iAG did not cause motion sickness and was associated with better self-motion perception during AG ramp-down. Additionally, both AG groups had superior cognitive performance while undergoing AG relative to controls; this may reflect attention or motivation differences between the groups.

Keywords: artificial gravity; cognition; head-down tilt bed rest; sensorimotor; spaceflight.

FIGURE 1

Testing Timeline. Entering head-down tilt bed rest (HDBR) occurred on day 0. Cognitive and sensorimotor measures were collected at various points before, during and following HDBR. Peri-centrifugation tasks only occurred during HDBR. Filled black dots represent data collection time points for the Purdue Pegboard and cognitive assessments. The open filled black circles represent the data collection time points of the posture and balance tasks. The half-filled dot indicates that all sensorimotor and cognitive assessments were collected at that time. The blue dots represent the peri-centrifugation task collections. The day relative to entering HDBR upon which the data were collected is plotted. Only data collection time points used for statistical analysis are included in this figure.

FIGURE 2

Functional Mobility Test (FMT) performance changes pre- to post-HDBR and post-HDBR recovery. HDBR resulted in a significant increase in completion time (p = 0.0002) for all subjects regardless of AG group. Completion time recovered to pre-HDBR levels by 10 days post-HDBR (p = 0.013). Significant differences are noted by *.

FIGURE 3

Balance (SOT-5M) changes from pre-HDBR to post-HDBR and post-HDBR recovery. The Sensory Organization Task 5 with head movements (SOT-5M) performance changes in Equilibrium Score indicate an effect of HDBR on balance performance for all groups regardless of AG (p = 0.0002). There was a significant recovery of performance post-HDBR (p = 0.043). Significant differences are noted by *.

FIGURE 4

Paced Auditory Serial Addition Task (PASAT) changes during HDBR. PASAT accuracy results indicate that both AG groups performed with higher accuracy throughout HDBR (p = 0.015) than the control group, although all groups increased accuracy through HDBR (p = 0.0001). There was also a significant group by time interaction (p = 0.01) for PASAT reaction times. Significant differences are noted by *.

FIGURE 5

Motion Sickness Response throughout HDBR. Motion sickness response scores indicate a significant group difference between the two AG groups, cAG and iAG, that is maintained throughout the entirety of HDBR (p = 0.04). This group difference is noted by the * in the figure. The iAG group had less motion sickness than the cAG group. There is also a significant group by HDBR interaction of these two AG groups (p = 0.032).

FIGURE 6

Post-AG Illusory Motion throughout HDBR. Post-AG response times indicate that iAG had a lower level of post-AG illusory motion (p = 0.036), indicating that they perceived coming to a stop sooner than the cAG participants.