What Being in Space Does to Your Brain

The human body has no business being in space. Without the familiar tug of gravity, bones can decalcify, muscles can atrophy, blood pressure can plunge, heart rate can grow erratic, and fluids can rise and pool in the head, leading to pain, congestion, vision problems, and even kidney stones as less water is flushed and excreted as urine. Exercise and proper hydration can alleviate some of these problems, but any stay in space can still exact a price—especially the long, six- to 12-month shifts that many space station astronauts pull. And that’s only the physical toll. Less studied, but no less worrisome, is what long-duration space flight can do to an astronaut’s cognitive abilities.

Now, a new study published in Frontiers in Physiology has some answers—mostly encouraging. While the brain, like the rest of the body, can take a hit when it leaves the planet, the investigators found that astronauts for the most part keep their intellectual and behavioral wits about them, adapting dependably, if sometimes slowly, to their rarefied surroundings.

The research, led by neuropsychologist Sheena Dev, of NASA’s behavioral health and performance laboratory, was extensive. It involved 25 astronauts who underwent a battery of 10 different cognitive tests before, during, and after six-month rotations aboard the International Space Station. The subjects sat for the first set of tests 90 days before leaving Earth. This provided a baseline against which their later performance could be measured. They followed that up by repeating the exercises during their first and last months aloft, and then again ten days and 30 days after returning to Earth.

There were a lot of reasons to expect the subjects’ performance to suffer as a result of their time in space. Among the psychological and emotional factors Dev and her colleagues considered were isolation, confinement, distance from home, overwork, disruption of circadian rhythms, and sleep deprivation. 

“Even on Earth, processing speed, working memory, and attention are cognitive domains that can show temporary changes when an individual is under stress,” said Dev in a statement that accompanied the release of the study. “If you happen to have a really busy day, but couldn’t get much sleep the night before, you might feel like it’s hard to pay attention, or that you need more time to complete tasks.”

Microgravity and exposure to cosmic radiation were also seen as potential variables contributing to cognitive decline. While Dev and her colleagues did not speculate exactly how these factors could create problems, they did not rule out damage to brain tissue and the central nervous system. 

Before beginning the cognitive exercises, the astronauts would report how many hours of sleep they had gotten the night before and what their current level of alertness was on a zero to 10 scale. That would help determine if any deficits in their performance were due to immediate, transient factors or longer-term, background stressors. Each of the tests they then took was designed to measure a particular cognitive skill. 

In one test called the Visual Object Learning Task, for example, they were shown three-dimensional figures, instructed to memorize them, and then required to pick them out of a later, larger assortment of shapes. In the Emotion Recognition Task, they were shown photographs of people exhibiting a range of emotions and told to identify them as either happy, sad, angry, fearful, or emotionless. In the Matrix Reasoning Task they were shown a series of shapes that changed according to a predictable pattern—though one shape was missing from somewhere in the middle of the sequence. They were then required to look at a number of other shapes and find the one that correctly completed the pattern. In the Balloon Analog Risk Test they played a video game in which they attempted to inflate an on-screen balloon as large as possible without popping it. The more pumps of imaginary air they gave it the more points they would win, unless they inflated it too much and it popped. That test was less a measure of the astronauts’ cognitive skills than their willingness to take chances in pursuit of a larger reward as opposed to playing it safe for a smaller but guaranteed one.

The good news—for both the individual subjects and the larger human enterprise of traveling in space—is that the astronauts’ abilities did not significantly decline across the pre-flight, in-orbit, and post-flight months. “Astronaut performance was stable throughout the flight,” says Dev. “[There was] no evidence of significant impairment or neurodegenerative decline.”

But that’s not to say space travel took no toll at all. The astronauts’ processing speed, working memory, and attention were all slower in space than they were on Earth—with assigned tasks taking at least a little longer to complete—but no less accurate. Not all of the faculties were recovered at the same time or to the same extent. Reduced ability to pay attention, for example, was evidenced only early in the mission before eventually rebounding, while processing speed stayed slightly slower throughout the entire six months in space before returning to normal when the astronauts were back on Earth. 

Performance on the emotion recognition task improved throughout the mission—an overall plus when it comes to living and working with other people in close quarters. Risk tolerance, as evidenced by the balloon test, declined over the six months in space, with the astronauts showing less inclination to pump the balloon to bursting—a result, perhaps, of an overall tendency toward caution bred of living in an inherently dangerous environment. Performance on the Matrix Reasoning Task—the pattern completion exercise—improved steadily throughout the time in space.

“Even in areas with observed declines, astronauts were still able to compensate and effectively complete their tasks,” Dev said in a statement.

Six months, of course, is only a fraction of the time future crews will spend in space—less even than the eight-month minimum it takes to get to Mars, never mind the time spent on the surface and the trip back home. But the current results do show that a species that came of age exploring its own planet may well have the temperamental and neurological wherewithal to go much farther—for much longer. 

As Dev summed up: “Living and working in space was not associated with widespread cognitive impairment that would be suggestive of significant brain damage.”