Effects of the cranial irradiation with high-energy protons on visuomotor task performance in non-human primates
Abstract
During long-duration space missions exposure to galactic cosmic rays, consisting mostly of protons (92%), leads to unavoidable early damage to perceptive, integrative and executive brain systems of humans. This may disturb operator activity of astronauts, which requires correct interaction among these systems. Therefore, the exact influence of proton irradiation on human operator activity should be studied in model experiments. Primates are the most adequate model animals for such experiments as their oculomotor behaviour and its physiological mechanisms are similar to human.
In present study we used two male monkeys (Macaca mulatta). One monkey (O+) was exposed to a single cranial proton irradiation (170meV, 3Gy) and for the control animal (O-) irradiation was simulated. The animals were trained to perform conditioned instrumental task involving saccadic and manual reactions. Monkeys were to fix gaze on a small square in the centre of the visual field and then execute a saccade to peripheral stimulus, fix gaze on it and respond to its dimming by pressing manually the ipsilateral lever. The peripheral stimuli of different eccentricities were presented in 34 locations, simulating visual navigation within visual field of 39x26 deg. Only correct responses were rewarded. The experimental session was terminated if incorrect responses occurred in more than 10% of trials, making the number of trials in one experimental session (NT per session) a measure of motivation of an animal. Evaluation of coherence of complex processes such as attention focusing and movement programming and execution is based on assessment of saccade latencies (SLs) and manual reaction latencies (MLs). Performance efficacy of both animals was relatively unaffected in course of 3 month after irradiation (a.i.) and remained in the range from 80% to 90%; slight increase can be explained by prolonged learning (O+: r=0.413, p=0.036; O-: r=0.361, p=0.02). In the same time, NT per session decreased significantly in consecutive experimental sessions in irradiated animal (r=-0.624, p<0.001), while control animal showed no significant decrease in this parameter (r=-0.156, p=0.329). This suggests decrease in motivation occurring contrary to slight increase in efficacy in exposed monkey. As to temporal properties of operator activity, we noticed slight (4-5% ) and substantial (11-17% ) increases in saccade latencies (SLs) of O+ monkey at the 32nd and from the 63rd to the 87th days a.i., respectively (r=0.543, p=0.013). SLs of O- monkey insignificantly decreased in the same period (r=-0.337, p=0.093). Manual reaction latencies (MLs) of O+, but not O-, demonstrated similar dynamics: there was a substantial increase (13-20%) from the 46th to the 87th day a.i. (r=0.555, p=0.007). In O+ both parameters returned to normal level by the 94th day a.i.. We can conclude that irradiation had a transient negative effect on eye and hand movements control in O+ while no effect was noticed in O-.\hspace{6mm} These results demonstrate that proton irradiation can substantially affect brain motivation circuits without decrease in performance efficacy, while complex visuomotor processes are generally resistant to the effects of proton irradiation, although a significant early temporary decrease in SLs and MLs can be noticed. This suggests existence of early and transient negative effects of radiation on mechanisms of attention focusing, movements programming and their execution. The research was funded by Russian Fund of Basic Research (project No. 17-29-01027).- Publication:
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43rd COSPAR Scientific Assembly. Held 28 January - 4 February
- Pub Date:
- January 2021
- Bibcode:
- 2021cosp...43E1829S