Comparison of the effects of partial- or whole-body exposures to ¹⁶O particles on cognitive performance in rats.

Studies using a ground-based system (NASA Space Radiation Laboratory) to examine the effects of exposure to high-energy charged particles or HZE particles on cognitive performance have interchangeably used whole-body exposures or exposures restricted to the head of the subject. For this study, we hypothesized that different types of exposure such as whole body vs. head only vs. body only might modulate the impact of irradiation on cognitive performance in different ways with the resulting cognitive performance outcomes being either independent of exposure type or strongly dependent on exposure type with each producing performance outcomes. To test these possibilities, three groups of rats were exposed to ¹⁶O particles (1,000 MeV/n): (1) head only; (2) body only; (3) whole body. Cognitive performance was measured using the elevated plus-maze, novel object recognition, spatial location memory and operant responding on an ascending fixed-ratio schedule. The results indicated that the performance of the rats on the spatial location memory task was markedly different when they received head-only irradiation compared to whole-body exposure. For the operant responding task, irradiation of the whole body resulted in a more severe performance decrement than exposures restricted to the head. The results are discussed in terms of nontargeted effects of HZE particles and the findings suggest that studies that utilize different patterns of exposure may not be directly comparable and that astronauts may be at a greater risk for HZE particle-induced cognitive deficits than previously thought.