One day, astronauts might travel through the solar system onboard spinning spaceships. Can human brains adapt?
July 23, 2004: Next time you go to a playground, try this: Bring along a ball and a friend, and get on the merry-go-round. Try throwing the ball to your friend across the ride from you, or even just a few feet beside you, and see if they can catch it on the first attempt.
They won't be able to, guaranteed. In fact, your throw will be way off. You'll feel your arm pulled strangely to one side as you make the throw, and once in flight, the ball will veer wildly.
Physicists call this the "Coriolis effect," and it happens on any spinning platform. Hurricanes swirl because of the Coriolis effect, the spinning platform being Earth itself. Contrary to popular belief, Coriolis forces do not control your bathroom drains--Earth doesn't spin that fast. But playing ball on a merry-go-round is definitely a Coriolis experience.
Space travel could be a Coriolis experience, too.
The problem is, spinning spaceships also come with a strong Coriolis effect. Tossed objects veer. Reach out to touch a button ... and your finger lands in the wrong spot. Could astronauts adapt to this? And if so, could they adapt well enough to perform dependably in the life-threatening environment of space?
That's what researchers James Lackner and Paul DiZio are trying to figure out. With support from NASA's Office of Biological and Physical Research, these two scientists are performing a series of experiments with people in rotating chambers to learn how well astronauts might adjust to life onboard spinning spaceships. They also hope to find training techniques that could help ease the transition from non-spinning to spinning, and back again.
Above: An artist's concept of a spinning spaceship. Click to view a 300 kb Quicktime movie of the Mars-bound ship in motion. Credit: John Frassanito & Associates, Inc.
"Experiments done in the 1960s seemed to show that people did not adapt well to rotation," says Lackner, the Meshulam and Judith Riklis Professor of Physiology at Brandeis University in Waltham, Massachusetts. "But in those experiments, the subjects didn't have well-defined goals for their movements. We've found that when a specific goal is given for the motion, people adapt rather quickly."
Given specific motion goals (such as reaching out to touch a target), people in their study learned to move accurately after only 10 to 20 attempts. Such a rapid adjustment surprised the researchers.
Says DiZio, an associate professor of psychology at Brandeis, "we speculate that when a goal is present, the brain dictates the desired motion to the muscles more precisely. Deviations from that motion are detected more readily by sensory feedback to the brain."
Why should people have this natural ability to adapt to rotation?
Our bodies and brains might have evolved, to a degree, to deal with the Coriolis effect. Every time you turn and reach for something simultaneously, you have a brief Coriolis experience. Turning atop an office chair. Playing basketball. Spinning to see what made that strange noise behind you! In each case, your brain makes on-the-fly Coriolis adjustments.
Right: A rotating room used by Lackner and DiZio in their experiments at the Ashton Graybiel Spatial Orientation Laboratory, Brandeis University. [More]
Other discoveries surprised the researchers, too. For example, after rotating for a while, people in their study no longer perceived the Coriolis effect. The veering pull on their arms and legs seemed to vanish. Their brains had compensated for it, so their minds no longer took notice of it.
Even stranger, when test-subjects first return to a non-rotating environment, they report feeling a Coriolis-pull in the opposite direction. It's just a trick of the mind, notes DiZio. After another 10 to 20 attempts at a goal-oriented motion, their brains readjust to the non-rotating world, and the phantom effect goes away.
DiZio and Lackner have found that people can adapt to rotational speeds as fast as a carnival-ride-like 25 rpm. That's about as fast as people turn their bodies during day-to-day life. For comparison, a spinning spaceship would likely rotate more slowly, perhaps 10 rpm, depending on the size and design of the craft.
Below: James Lackner (left) and Paul DiZio (right) are co-directors of the Ashton Graybiel Spatial Orientation Laboratory at Brandeis University. [More]
To exert more control over the conditions of their experiment, the researchers have tried something innovative: simulating the Coriolis effect with a robotic arm. Seated subjects would try to make certain motions with their arm while the robotic arm gently pulls on their wrist in a way that mimics the Coriolis effect.
The advantage of this approach is that the robotic arm can be reprogrammed to pull in a variety of ways, thus testing how subjects respond to different conditions. Using the arm, DiZio and Lackner have discovered that people can adapt to a small, variable force even when it's masked by a larger, constant force. So, for example, astronauts should be able to adapt to a variable Coriolis effect in spite of some constant background force, such as the steady push of a spacecraft's ion-propulsion thrusters.
Many questions remain un-answered. Do results based on arm motions apply to the whole body? Does carrying heavy tools make a difference? After adapting once, can a person re-adapt more easily later? What's the best way to train astronauts for life in a rotating home?
Lackner and DiZio plan to tackle these questions and more as their research continues in the months to come.