Prolonged exposure to these cosmic rays would also affect what's known as "fear extinction" -- a process which helps suppress unpleasant or stressful associations -- and potentially induce extreme anxiety. Understandably, this could spell out big, big trouble for anyone who's hundreds of millions from home and surrounded by nothing but black nothingness.
So why doesn't this sort of thing happen to astronauts like Scott Kelly, who have spent a hell of a long time floating around the International Space Station without any problems? It's because visitors to the ISS aren't exposed to the same types of dangerous rays, since it orbits within the earth's protective magnetosphere.
It's not necessarily a foregone conclusion that anyone who dares travel to Mars is doomed to live with brain damage for the rest of their lives, though. The study points to some preventative measures worth looking into, including a special protective barrier area of the spacecraft where astronauts could retreat to sleep and spend down time, and a vaccine of sorts that would collect free radicals and prevent them from entering your brain.