Sleep fragmentation exacerbates executive function impairments induced by protracted low dose rate neutron exposure

Abstract

Purpose

Astronauts on the planned missions to Mars are expected to have to work more autonomously than on previous missions. Thus mission success may be influenced by the astronauts’ ability to respond quickly to unexpected problems, processes that require several executive functions. The purpose of this study was to determine the impact that prolonged low dose and low dose rate exposure to neutrons had on two executive functions, and whether the severity and incidence of cognitive impairment was altered by sleep fragmentation.

Materials and methods

In this study we assessed the impact that prolonged (six month) low dose rate neutron exposure had on the ability of male Wistar rats to perform in two executive function tasks (i.e. attentional set shifting (ATSET) – a constrained cognitive flexibility task and the UCFlex assay – an unconstrained cognitive flexibility task). In recognition of the fact that astronauts also have to contend with inadequate sleep quantity and quality for much of their time in space, we determined the impact that relatively mild sleep disruption had on the ability to perform in the ATSET test in sham and neutron-irradiated rats.

Results

Chronic low dose (18 cGy) and dose-rate (1 mGy/day) exposure of rats to mixed neutron and photon over the course of six months resulted in significant impairment of simple discrimination (SD) performance. Should similar effects occur in astronauts subjected to low dose rate exposure to Space Radiation, the impairment of SD performance would result in a decreased ability to identify and learn the ‘rules’ required to respond to a new task or situation. Analysis of the behavioral data by kernel density estimation revealed that 40% of rats had severe ATSET impairments. This value may be a best-case scenario because exposure to neutrons also adversely impacted performance in the UCFlex task. Furthermore, when the good performing rats were reevaluated after they had been subjected to sleep fragmentation, additional ATSET performance decrements were observed in the set shifting stages of the ATSET test, with only 7.4% of the neutron exposed rats able to successfully perform ATSET under normal and sleep fragmented conditions, as opposed to ∼55% of shams.

Conclusion

Protracted low dose and low dose rate neutron exposures impairs executive functions in a high percentage of rats that were normally rested, however further detriments in performance become evident when the rats are subjected to sleep fragmentation.

Keywords:

• Space radiation
• neutrons
• executive function
• sleep fragmentation
• creative problem solving
• attentional set shifting

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was funded by NASA grant support [NNX15AI22G] and [NNX16AC40G].

Notes on contributors

Richard A. Britten

Richard A. Britten, Ph.D., is a Professor of Radiation Oncology at the Eastern Virginia Medical School, Norfolk, VA, USA.

Vania D. Duncan

Vania D. Duncan, BS, is a research associate in the Department of Radiation Oncology at the Eastern Virginia Medical School, Norfolk, VA, USA.

Arriyam S. Fesshaye

Arriyam S. Fesshaye, M.S., is a research associate in the Department of Radiation Oncology at the Eastern Virginia Medical School, Norfolk, VA, USA.

Laurie L. Wellman

Laurie L. Wellman, Ph.D., is an Associate Professor of Pathology and Anatomy at the Eastern Virginia Medical School, Norfolk, VA, USA.

Christina M. Fallgren

Christina M. Fallgren, BS, is a research associate in the Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO, USA.

Larry D. Sanford

Larry D. Sanford, Ph.D., is a Professor of Pathology and Anatomy at the Eastern Virginia Medical School, Norfolk, VA, USA.