- Email: [email protected]
Space particles play with the mind
Lights fantastic Astronauts can see them even with their eyes closed. Are these mysterious flashes just a space oddity or a serious space hazard, asks Stuart Clark IT’S hardly unusual to find things flashing into your head as you fall asleep, but as Christer Fuglesang was settling down on his first night aboard the International Space Station it happened quite literally. It was December 2006, and as the European Space Agency astronaut floated, eyes closed, in his sleeping bag he suddenly saw a spot of white light surrounded by a faint halo. It vanished in an instant but Fuglesang realised immediately what it was. “I had heard about these things and so was very happy to have finally experienced one,” he says. Since Buzz Aldrin and Neil Amstrong first reported these flashes during the Apollo 11 mission to the moon in 1969, dozens of astronauts have seen them. An investigation by NASA after Apollo 11 returned concluded that the flashes, sometimes called “phosphenes”, were a consequence of fast-moving particles, most probably cosmic rays, zipping through the eyeball. The investigation suggested that this was harmless. Now fresh evidence is calling some of these conclusions into question. The particles that cause the light flashes may be directly interacting with the brain by stimulating the brain’s visual processing unit, says Livio Narici, a physicist at Italy’s National Institute for Nuclear Physics in Rome. And that’s a worry – for two reasons.
PHILIP LEE HARVEY/RISER/GETTY
G
www.newscientist.com
31 May 2008 | NewScientist | 39
to look into it further. The experiment he devised wasn’t particularly subtle: McNulty and his colleagues simply placed their heads in front of a beam of muons from a particle accelerator at Princeton University and described what they saw. “Princeton made it a condition of the experiment that we would not use graduate students as targets,” McNulty recalls, so the students operated the particle beam while the professors took turns to stand in the firing line. Though they established that some bright flashes were caused by Cerenkov radiation, it also became clear that this couldn’t be the only mechanism involved. In one experiment they placed a lead shield in the beam to slow down the particles to below the speed required to produce a Cerenkov flash – yet the professors still saw phosphenes. McNulty suggested that particles smashing into nerve cells behind the eye produce fragments that knock electrons from nearby atoms, creating a tiny electric current. This, he suggested, could be picked up by the optic nerve and interpreted in the brain
NASA/SPL
First, there is the well-being of astronauts. “We do not know yet whether there are longterm health effects,” says Narici. This is less of a concern for astronauts on the space shuttle or the International Space Station (ISS), where the Earth’s magnetic field keeps the majority of these particles at bay, but it could be a different story on missions to a moon base or Mars lasting months or years. Then there is the effect on astronauts’ perception. If these particles can affect the visual cortex, they might also act on other regions of the brain. Astronauts so affected might suddenly smell strange odours or hear mysterious noises. What if this were to happen during a tricky landing sequence, when a moment’s distraction could spell disaster? One thing not in doubt is that phosphenes are a common experience even in Earth orbit. According to a survey organised by Fuglesang, 80 per cent of astronauts see these flashes of light while they are in space. Most appear while their eyes are closed, with 12 of the 59 respondents saying that the flashes
“Astronauts so affected might suddenly smell strange odours or hear mysterious noises” disturbed their sleep. Three respondents reported seeing them with their eyes open, in bright light. None reported any unusual nonvisual sensations, however. The results were published in the journal Aviation, Space, and Environmental Medicine in 2006 (vol 77, p 449). Space is full of high-energy particles travelling at close to the speed of light, and this leads to some interesting effects when they enter the body. The speed of light passing through the aqueous humour inside the eyeball, for example, is slower than in the vacuum of space, so a cosmic-ray particle entering the eye can exceed this speed, causing the optical equivalent of a sonic boom – a flash of light known as Cerenkov radiation. This was the mechanism suggested by the original NASA investigation, but in the early 1970s Peter McNulty, then at Clarkson College of Technology in Potsdam, New York, decided
40 | NewScientist | 31 May 2008
as a flash of light. Although McNulty’s team could not prove this hypothesis, their explanation seemed sufficiently plausible for the investigation to stop there. McNulty’s experiment appeared to rule out the possibility that direct stimulation of the visual cortex was causing the flashes. He tried irradiating other parts of his brain, including the visual cortex, but saw nothing. However, Narici believes these muon-beam experiments missed something, and that the particles which astronauts meet in space may behave differently. So he is taking a second look, and has devised an experiment that will be flown up to the ISS later this year. This was prompted in part by experiments carried out by Giles Brindle and Walpole Lewin at the University of Cambridge in 1968. The experiments were aimed at trying to stimulate the visual cortex, as a possible way to help
restore the sight of people who had become blind. The experimenters implanted electrodes close to the visual cortex of a 52-year-old blind person and sure enough, when they sent a current directly into the brain, the patient reported seeing flashes of light “like a star in the sky”. This surgery was invasive, and the electronics were too bulky to be practicable, so the research was eventually abandoned. But Narici and vision specialist James Morrison at the University of Glasgow, UK, suspect that Brindle and Lewin were onto something. “Medical experiments show that delivering energy to the visual cortex gives light flashes,” Narici says. “I really believe that it is not just all in the eye.” He and Morrison believe that the visual system could be particularly susceptible to influence by high-speed particles. A quarter of the brain is involved in
www.newscientist.com
Without the Earth’s magnetic field to shield them, astronauts could be vulnerable to phosphenes
sight: from the eyes through the optic nerve to the visual cortex at the rear of the skull. “It is the longest pathway in the brain. It is perfectly feasible that particles in space are having a direct effect upon it,” says Morrison. Information that Narici has received from some of the participants in the early beam tests suggest that energetic particles can affect other senses too. They say they perceived strange smells during the experiments, perhaps indicating direct stimulation of the olfactory bulb, which lies in the front of the brain. The researchers say they did not publish these observations because the effect seemed to be more subjective than spotting the appearance of a light flash. To tie down the mechanism once and for all, Narici would love to follow McNulty’s example and stick his head in a beam of particles. “That would be the best experiment,”
www.newscientist.com
he says. “But I can’t see the ethics committee agreeing to this today.” His experiment aboard the ISS is the next best thing. Called Anomalous Long Term Effects in Astronauts’ Central Nervous System (ALTEA), it is a souped-up version of experiments that Narici and his colleagues have been running for about a decade, both on Earth and in space. Participating astronauts wear a helmet surrounded by six particle detectors, each one the size of a shoebox. Every time the astronaut sees a light flash, he or she pushes a button to time-stamp the event. Meanwhile, the detectors track the incoming particles closely enough to show where each one is heading. “We can actually follow a particle into the brain,” says Narici. The researchers can then analyse the data to discover whether the phosphenes correlate with particle hits, and if so whether the particle is heading for the eye,
the optic nerve or the visual cortex. Astronauts will wear the helmet for about an hour at a time, during which they might typically expect to see up to 10 phosphenes. One experiment on the Mir space station with an early version of Narici’s helmet clocked up 233 flashes in 26 hours, whereas a later experiment on the ISS logged just 20 flashes in 7 hours. Clearly not every particle causes a phosphene, as there are on average around 20 particles a minute passing through an astronaut’s eyes alone. This makes it difficult to match the light flash to a particular particle, so to help work out what is happening, Narici’s latest helmet is fitted with electrodes linked to an electroencephalograph (EEG). By constantly monitoring activity in the brain, the EEG should reveal which parts of an astronaut’s brain are affected when a phosphene is perceived. In parallel with the ALTEA experiment, Narici is coordinating experiments down on the ground. One is running at the synchrotron belonging to the Society for Heavy-Ion Research in Darmstadt, Germany. Here, people with brain tumours are exposed to a beam of carbon atoms designed to shrink the cancer. In the process many have reported seeing phosphenes. Narici is collating these observations, along with details of the beam’s path through the brain. He also has laboratory experiments running to see whether the effect can be modelled in mice, and whether reactions in the light-sensitive protein rhodopsin, which plays a key role in vision, can be triggered by energetic charged particles. “I have a feeling that the light flashes are just the tip of the iceberg,” he says. And one way or another, he intends to unravel the mysteries that lie beneath the surface. G Stuart Clark is a science journalist based in London. His latest book is Deep Space, published by Quercus Further reading: “Positive visual phenomena in space: A scientific case and a safety issue in space travel” by Walter G. Sannita, Livio Narici and Piergiorgio Picozza, Vision Research, vol 46, p 215
31 May 2008 | NewScientist | 41
PHILIP LEE HARVEY/RISER/GETTY
G
www.newscientist.com
31 May 2008 | NewScientist | 39
to look into it further. The experiment he devised wasn’t particularly subtle: McNulty and his colleagues simply placed their heads in front of a beam of muons from a particle accelerator at Princeton University and described what they saw. “Princeton made it a condition of the experiment that we would not use graduate students as targets,” McNulty recalls, so the students operated the particle beam while the professors took turns to stand in the firing line. Though they established that some bright flashes were caused by Cerenkov radiation, it also became clear that this couldn’t be the only mechanism involved. In one experiment they placed a lead shield in the beam to slow down the particles to below the speed required to produce a Cerenkov flash – yet the professors still saw phosphenes. McNulty suggested that particles smashing into nerve cells behind the eye produce fragments that knock electrons from nearby atoms, creating a tiny electric current. This, he suggested, could be picked up by the optic nerve and interpreted in the brain
NASA/SPL
First, there is the well-being of astronauts. “We do not know yet whether there are longterm health effects,” says Narici. This is less of a concern for astronauts on the space shuttle or the International Space Station (ISS), where the Earth’s magnetic field keeps the majority of these particles at bay, but it could be a different story on missions to a moon base or Mars lasting months or years. Then there is the effect on astronauts’ perception. If these particles can affect the visual cortex, they might also act on other regions of the brain. Astronauts so affected might suddenly smell strange odours or hear mysterious noises. What if this were to happen during a tricky landing sequence, when a moment’s distraction could spell disaster? One thing not in doubt is that phosphenes are a common experience even in Earth orbit. According to a survey organised by Fuglesang, 80 per cent of astronauts see these flashes of light while they are in space. Most appear while their eyes are closed, with 12 of the 59 respondents saying that the flashes
“Astronauts so affected might suddenly smell strange odours or hear mysterious noises” disturbed their sleep. Three respondents reported seeing them with their eyes open, in bright light. None reported any unusual nonvisual sensations, however. The results were published in the journal Aviation, Space, and Environmental Medicine in 2006 (vol 77, p 449). Space is full of high-energy particles travelling at close to the speed of light, and this leads to some interesting effects when they enter the body. The speed of light passing through the aqueous humour inside the eyeball, for example, is slower than in the vacuum of space, so a cosmic-ray particle entering the eye can exceed this speed, causing the optical equivalent of a sonic boom – a flash of light known as Cerenkov radiation. This was the mechanism suggested by the original NASA investigation, but in the early 1970s Peter McNulty, then at Clarkson College of Technology in Potsdam, New York, decided
40 | NewScientist | 31 May 2008
as a flash of light. Although McNulty’s team could not prove this hypothesis, their explanation seemed sufficiently plausible for the investigation to stop there. McNulty’s experiment appeared to rule out the possibility that direct stimulation of the visual cortex was causing the flashes. He tried irradiating other parts of his brain, including the visual cortex, but saw nothing. However, Narici believes these muon-beam experiments missed something, and that the particles which astronauts meet in space may behave differently. So he is taking a second look, and has devised an experiment that will be flown up to the ISS later this year. This was prompted in part by experiments carried out by Giles Brindle and Walpole Lewin at the University of Cambridge in 1968. The experiments were aimed at trying to stimulate the visual cortex, as a possible way to help
restore the sight of people who had become blind. The experimenters implanted electrodes close to the visual cortex of a 52-year-old blind person and sure enough, when they sent a current directly into the brain, the patient reported seeing flashes of light “like a star in the sky”. This surgery was invasive, and the electronics were too bulky to be practicable, so the research was eventually abandoned. But Narici and vision specialist James Morrison at the University of Glasgow, UK, suspect that Brindle and Lewin were onto something. “Medical experiments show that delivering energy to the visual cortex gives light flashes,” Narici says. “I really believe that it is not just all in the eye.” He and Morrison believe that the visual system could be particularly susceptible to influence by high-speed particles. A quarter of the brain is involved in
www.newscientist.com
Without the Earth’s magnetic field to shield them, astronauts could be vulnerable to phosphenes
sight: from the eyes through the optic nerve to the visual cortex at the rear of the skull. “It is the longest pathway in the brain. It is perfectly feasible that particles in space are having a direct effect upon it,” says Morrison. Information that Narici has received from some of the participants in the early beam tests suggest that energetic particles can affect other senses too. They say they perceived strange smells during the experiments, perhaps indicating direct stimulation of the olfactory bulb, which lies in the front of the brain. The researchers say they did not publish these observations because the effect seemed to be more subjective than spotting the appearance of a light flash. To tie down the mechanism once and for all, Narici would love to follow McNulty’s example and stick his head in a beam of particles. “That would be the best experiment,”
www.newscientist.com
he says. “But I can’t see the ethics committee agreeing to this today.” His experiment aboard the ISS is the next best thing. Called Anomalous Long Term Effects in Astronauts’ Central Nervous System (ALTEA), it is a souped-up version of experiments that Narici and his colleagues have been running for about a decade, both on Earth and in space. Participating astronauts wear a helmet surrounded by six particle detectors, each one the size of a shoebox. Every time the astronaut sees a light flash, he or she pushes a button to time-stamp the event. Meanwhile, the detectors track the incoming particles closely enough to show where each one is heading. “We can actually follow a particle into the brain,” says Narici. The researchers can then analyse the data to discover whether the phosphenes correlate with particle hits, and if so whether the particle is heading for the eye,
the optic nerve or the visual cortex. Astronauts will wear the helmet for about an hour at a time, during which they might typically expect to see up to 10 phosphenes. One experiment on the Mir space station with an early version of Narici’s helmet clocked up 233 flashes in 26 hours, whereas a later experiment on the ISS logged just 20 flashes in 7 hours. Clearly not every particle causes a phosphene, as there are on average around 20 particles a minute passing through an astronaut’s eyes alone. This makes it difficult to match the light flash to a particular particle, so to help work out what is happening, Narici’s latest helmet is fitted with electrodes linked to an electroencephalograph (EEG). By constantly monitoring activity in the brain, the EEG should reveal which parts of an astronaut’s brain are affected when a phosphene is perceived. In parallel with the ALTEA experiment, Narici is coordinating experiments down on the ground. One is running at the synchrotron belonging to the Society for Heavy-Ion Research in Darmstadt, Germany. Here, people with brain tumours are exposed to a beam of carbon atoms designed to shrink the cancer. In the process many have reported seeing phosphenes. Narici is collating these observations, along with details of the beam’s path through the brain. He also has laboratory experiments running to see whether the effect can be modelled in mice, and whether reactions in the light-sensitive protein rhodopsin, which plays a key role in vision, can be triggered by energetic charged particles. “I have a feeling that the light flashes are just the tip of the iceberg,” he says. And one way or another, he intends to unravel the mysteries that lie beneath the surface. G Stuart Clark is a science journalist based in London. His latest book is Deep Space, published by Quercus Further reading: “Positive visual phenomena in space: A scientific case and a safety issue in space travel” by Walter G. Sannita, Livio Narici and Piergiorgio Picozza, Vision Research, vol 46, p 215
31 May 2008 | NewScientist | 41