EFFECTS OF LOWER BODY NEGATIVE PRESSURE AND EXERCISE DURING 30 DAYS OF STRICT HEAD-DOWN-TILT BED REST ON VISUAL SEARCH PERFORMANCE AND ASSOCIATED OCULOMOTOR METRICS

Abstract

Human space exploration requires appropriate countermeasures against spaceflight-related environmental stressors to ensure astronauts’ health. Microgravity as one of these stressors has been observed to cause a variety of ocular symptoms, referred to as spaceflight-associated neuro-ocular syndrome (SANS). Current research suggests that SANS and spaceflight-associated cognitive impairments might be attributable to a shared mechanism: a microgravity-induced headward fluid redistribution [1]. During SANS CM, a NASA study recently conducted at German Aerospace Center’s :envihab, microgravity was simulated via 30 days of 6° Head-Down-Tilt Bed Rest (HDBR). The aim of SANS CM was to evaluate the effectiveness of two countermeasures against the headward fluid shift and consequently, SANS. The first countermeasure group was treated with Lower Body Negative Pressure (LBNP), the second one performed ergometer training with veno-occlusive thigh cuffs to induce prolonged fluid accumulation in the lower extremities. One ‘optimal’ control group was exposed to reinstated gravity along the upright body axis by daily upright sitting, and one strict bed rest control group received no treatment. As an annex study, a cognitive test battery was conducted by the German Aerospace Center. Reaction speed, accuracy, and exploratorily, eye movements, were determined in two visual search tasks assessing selective attention. Measurements were effectuated one day before, on the last day, and after the bed rest phase. Results suggested negative effects of HDBR on reaction times in visual search tasks, while accuracy remained unaffected. LBNP did not counteract the reaction time deterioration during bed rest, but accelerated recovery. The exercise group was least affected, implying an adequate effectiveness against attentional and oculomotor changes. It has recently been suggested that due to a mechanism of sensory reweighting, HDBR also induces microgravity-related sensorimotor alterations [2,3]. In clinical contexts, exercise has long been used as a treatment against sensorimotor and vestibular deficits [4]. In a HDBR study, exercise has been demonstrated to have beneficial sensorimotor effects as well [5]. Since sensorimotor and vestibular information is also involved in saccadic activity [6], mainly through cerebellar contribution [7], it is possible that in addition to counteracting the headward fluid shift, exercise had further beneficial effects by counteracting HDBR-related sensorimotor changes. Therefore, it might have prevented simulated-microgravity-induced alterations of saccade planning and execution, and consequentially, visual search performance. Future studies should determine whether oculomotor metrics could be a sensitive diagnostic of more complex sensorimotor functions during HDBR, and how they are moderated by exercise.