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This raises a series of questions.

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What if we grew up in weightlessness instead? Does the balance system need inputs from gravity to develop and work properly? Would the pressure sensors in the cardiovascular system—and the connections they make—be normal if they were not stimulated by gravity? How would the postural muscles that work against gravity fare if they did not have the loading that gravity normally supplies? Several Neurolab experiments were focused on answering these questions, and the results were surprising. As shuttle crew members, we not only studied the brain and body changes that took place, but also, in many instances, directly experienced them.

Effects on our balance system, for example, were noticeable right after landing. Small changes in head position produced exaggerated sensations of motion. Also, my gait was unsteady, and, when I climbed stairs, it felt as if the stairwell were moving up and down as I took each step. I could get around, but I was moving much more slowly and carefully than I had before I left. The balance, or vestibular, system has gravity sensors. Resting on these hair cells are small calcium particles called otoliths. When the head moves, gravity exerts its pull on these particles, just as gravity affects the water in a level.

The movement of the otoliths bends the hair cells, and the brain uses this information to determine up, down, tilting, and acceleration. Using a novel electrode technology, a team of Neurolab researchers led by Stephen Highstein, M. Interestingly, 30 hours after returning to Earth, most of the obvious changes in my balance were gone, too.

Another team of Neurolab investigators, led by Muriel Ross, Ph. Synapses are the points of contact at which nerve cells communicate, either by sending and receiving chemical messengers or through electrical impulses. Although the number declined by day 14, Neurolab rats still had more synapses overall than control rats on the ground.

One hypothesis is that the additional synapses gave the rats more information they could use in adjusting to their new environment. Indeed, an increase in synapses is a routine way in which the brain adapts to its environment. Learning new physical skills, for example, produces new synapses in the part of the brain devoted to the task. Another study, led by Gay Holstein, Ph. The cerebellum, which is involved in movement coordination and motor learning, receives input from the gravity-sensing saccule and utricle.

The Neurolab studies also showed that on a spacecraft situations may exist where sensory information from the balance system is unreliable. During landing, when gravity has been reintroduced, a sudden gust of wind or unexpected roll of the spacecraft might lead the pilot to overcompensate drastically if he relies solely on the information about tilt or roll he perceives with a space-adapted balance system.


Information about balance gained through the Neurolab studies may also help researchers understand what happens to people with disorders that affect balance, such as vertigo or damage to the gravitational information pathways, which can occur with strokes and trauma. He had not been paralyzed—his muscles were fully functional—but Waterman had lost what is called position sense. The nerves carrying information about the location of his arms and legs from the sensors in muscles, tendons, and joints information critical to control body movements had been irreparably damaged by a rare neurodegenerative disease.

Waterman was advised to get used to life in a wheelchair. But Waterman was a proud man, and, by the force of will, he trained himself gradually to navigate through the world by using his other senses. Eventually, against all expectations, he returned to work. Because Waterman did not have position sense, he depended on vision and balance sense. Astronauts need to make a similar, although less dramatic, change. In space, they lose much of the information that the inner ear provided on Earth about movement.

This may be compensated by a greater dependence on vision. One of the experiments on Neurolab, led by Charles Oman, Ph.

If you have ever sat on a stationary train when the train on the next track started moving, you might have felt a strong, but erroneous, sense that you were moving. This misleading feeling that one is moving can be produced by using a virtual reality headset.

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The wearer views a scene that appears to be a long hallway with walls moving past the viewer on either side, sometimes producing the sense that the viewer is moving down the hallway, instead of the hallway moving past the viewer. On Neurolab, we had a virtual reality system that produced a scene like this. As soon as the scene began, the visual sense of motion was so strong that I instinctively put my hand out in front of me because I felt as though I was going to slam right into the rack. This reaction suggested that my brain had adapted in space and now was ranking visual information much more highly than on Earth.

Another experiment on Neurolab, designed by Alain Berthoz, Ph. The ball-catching experiment, described in Case 2, showed that the brain acted as though it assumed that the laws of gravity were still in operation and expected the ball to accelerate as it fell; therefore, arm muscles tightened before needed. This internal model, however, did adapt over time in weightlessness and became less pronounced.

Change history

Mental maps that help us know where we are and how to get where we want to go are another kind of internal model. We know we have these maps, because we can navigate around familiar places, such as our homes, in the dark. The maps are contained in the hippocampus, a part of our brain that gives us our sense of space, place, and visual recognition. They have lost the maps that once guided them.

In a study published in in Nature, a team of researchers traced navigation and image recognition to individual neurons. From animal studies, we know that such neurons develop their codes the link between a particular neuron and a particular place in the environment by using information from balance organs, position sense, and vision, as well as from external landmarks. But when lighting cues become weak, the internal clock can get out of synch with the environment. On Neurolab, we did not have a consistent 12 hours each of light and darkness; the sun rose or set every 45 minutes, and the light levels inside the shuttle were dim and often erratic.

In addition, we were following a hectic schedule and wanted to make sure we completed all the experiments successfully. If this meant missing part of our scheduled sleep time, we did. Sleeping was different in space. The Neurolab studies included a comprehensive look at sleep, circadian rhythms, and performance on the space shuttle, including a complete double-blind trial of the hormone melatonin for use in space. As the subjects of this study, on certain nights we wore suits with an array of sensors that measured our brain waves, respiration, and other biological activities. Our sleep-monitoring system provided the same data that a fully equipped sleep lab at a large research center could offer.

Continuous recordings from an activity meter worn on the nondominant wrist kept track of when we were active or resting. Measurements of body temperature from a pill we swallowed that measured temperature gave an indication of our circadian rhythms. The results showed we had less sleep, and of poorer quality, than on the ground.

Astronauts Study the Brain in Space

Our circadian rhythms moved out of synchrony with the day and night cycle on the shuttle. The schedule called for us to wake up 20 minutes earlier each day, so that sleeping and waking would be timed appropriately on the day of reentry, but our circadian rhythms could not keep up with this acceleration.

Unfortunately, melatonin had no more effect than a placebo on our ability to sleep at the scheduled time in space. Another study examining our breathing patterns during sleep found that, in weightlessness, snoring practically disappears, probably because without gravity there is no force pushing the tongue or tissues in the neck into the airways. Finally, studies upon return to Earth showed that the phase of sleep known as rapid eye movement, or REM, sleep increased.

But given the same test shortly after landing, more than half of the crew members had to sit down before the time was up. Some investigators had suspected that this was because their autonomic nervous systems had become less active or less sensitive in space. Surprisingly, Neurolab evidence failed to support the hypothesis that in space, without the stress of gravity, this system had become less sensitive.

Reading the neural code for space

In one experiment, Neurolab astronauts spent time in a clear plastic chamber that used suction on their legs to pull blood from the chest into the lower body, just as gravity does on Earth. In a Nobel prize-winning experiment, David Hubel, M. Even though the formerly sealed eye was not injured, the brain regions serving the eye needed visual input at critical times for the brain to develop normally.

Sealing the eye at a late stage of development had no effect. If this is true for vision, is there also a critical period when gravity must be present for the brain to develop normally? A cluster of Neurolab experiments looked at the effect of weightlessness on the development of gravity sensors and balance systems. One study by Michael Wiederhold, Ph. Eberhard Horn, Ph.

A study in rats by Jacqueline Raymond, Ph. Does proper wiring up of the balance system in the brain depend upon the effects of gravity? Perhaps the most striking results were observed in the studies on the development of complex movements, such as walking. Earth dwellers seem to enter life ready to walk. Many prey animals, such as deer and horses, try to stand almost immediately after birth. If you hold an infant rat on its back and then let it go, it will turn over, or right itself, in whatever way it can.

A group of young rats on the Neurolab mission were in space during the time when they would ordinarily have been learning to walk and right themselves. They felt no need to do so, because no input from the gravity sensors told them they were upside down. After returning to Earth, the rats could right themselves, but they never acquired the classic, smooth adult pattern.

Fewer dendrites protrusions that receive incoming signals in their motor neurons were involved in postural control and righting. The researchers, Kerry Walton, Ph. This provides more stimulation to the relevant areas of the brain, which could increase the number of synapses. Weight-bearing muscles show profound changes when they have no weight to bear. On Neurolab, an antigravity muscle called the soleus grew poorly in rats 8 days old at launch. Another study found that antigravity muscles were more impaired than muscles used for other tasks.

This suggests that weight-bearing activity is essential for muscle development; without it, production of key proteins is slowed. What would this imply for the human fetus developing under conditions of weightlessness, since in humans some 60 percent of muscles are weight-bearing or antigravity? In all, the development studies conducted on Neurolab suggest that crucial periods may exist in development when gravity must be present.

This brings up an interesting question. Although we evolved on Earth, could we as easily live anywhere else? Most of the Neurolab work illustrates the brain has astonishing adaptability, but the adaptability does not last forever. Nerve cells fired coordinated signals in brain organoids, 3-D clusters of cells that mimic some aspects of early brain development.

A potential link between strep throat and sudden mental disorders in children raises questions about how infections can alter the brain. Scientists watched brain activity in a region where reading takes root, and saw a hierarchy of areas that give symbols both sound and meaning. Nerve cells in an important memory center in the brain sync their firing and create fast ripples of activity seconds before a recollection resurfaces. Not a subscriber? Become one now. Skip to content. Science News Needs You Support nonprofit journalism.

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