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Into thin air: Altitude's toll on the brain

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Introduction

by David Dobbs
Editor, Mind Matters

"The mountains," wrote climbing enthusiast Sir Francis Younghusband, "reserve their choice gifts for those who stand upon their summits." Yet those who earn these gifts pay a unique price. As neuroscientist and weekend climber R. Douglas Fields relates below, a recent study used brain scans to examine both the effects that both one-time and cumulative high-altitude climbing have on the human brain. The findings are not elevating for those of us who love to climb.

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Brain Cells into Thin Air

by R. Douglas Fields
National Institutes of Mental Health

Washington, D.C.

 

"Mount Everest is very easy to climb, only just a little too high." - The Observer, Jan 25, 1953. Three attributes of a good mountaineer are high pain threshold, bad memory, and ... I forget the third. - R. Douglas Fields


Climbing Mount Everest is not so difficult; the hard part is getting down intact. According to a recent brain imaging study, almost no one does. Of thirteen climbers in the study who attempted Mount Everest, none returned without brain damage. The study also scanned the brains of climbers who attempted less extreme summits. For those of us who love to climb, the results are less than elevating. It seems that almost no one, whether the weekend warrior chaperoned to the summit or the seasoned mountaineer, will return from the high peaks with a brain in the same condition it was in beforehand. What Goes On in a Climber's Brain? The first scientific study of the effects of high altitude on the human brain were made by nineteenth century Italian physiologist Angelo Mosso, who made direct observations on a man whose brain was partly exposed as a result of an accident. Mosso, peeking into the man's skull, observed vague changes in swelling of the brain, but the crude methods available at the time limited his analysis. Now a similar experiment has been done with modern noninvasive brain imaging. In the study reviewed here, "Evidence of Brain Damage After High-Altitude Climbing by Means of Magnetic Resonance Imaging," neurologists Nicholas Fayed and colleagues at the Clinica Queron and Miguel Servet University Hospital in Zarogoza, Spain, gave MRI brain scans to 35 climbers (12 professionals and 23 amateurs) who had returned from high-altitude expeditions, including 13 who had attempted Everest. The results on the Everest climbers are the most stark. Of the thirteen climbers, three had made the summit, at 8480 meters, three had reached 8100 meters, and seven topped out between 6500 and 7500 meters. Though the expedition suffered no major mishaps and none of the 12 professional climbers suffered any obvious signs of high-altitude illness, only one of the 13 climbers returned with a normal brain scan. The brain scans showed that all but one climber suffered cortical atrophy and enlargement of the Virchow-Robin spaces. These are spaces surrounding brain blood vessels that drain brain fluid and communicate with the lymph system. Widening of these VR spaces is seen in the elderly, but rarely in young people. The amateur climber's brain had also suffered subcortical lesions in the frontal lobes. Signs Acute and Subtle A person's tolerance to hypoxia (lack of oxygen) varies according to differences in innate physiology and physical conditioning, which can help the body and brain better tolerate the exertion and physiological stresses of high-altitude mountaineering. But no one is immune to hypoxia's effects. The first stage of high altitude sickness is called acute mountain sickness, which can cause headache, insomnia, dizziness, fatigue, nausea, and vomiting. The next stage up in seriousness is high-altitude cerebral edema (that is, brain swelling), also known as HACE, which is potentially fatal. Both are rooted in the body's reaction to low levels of oxygen. Lack of oxygen to the brain directly impairs or damages brain cells. In addition, the walls of blood capillaries in the brain and elsewhere begin to leak at altitude, and this leaked fluid causes dangerous swelling, pressing the brain outward against the rigid skull. Sometimes the optic nerves swell so badly they bulge into the back of the eye, degrading vision and causing retinal hemorrhages. Meanwhile, blood, concentrated from dehydration and thickened by increased numbers of red blood cells, more easily clots, and this clotting, along with the hemorrhage from the thinned capillaries, increases the chance of stroke. A climber suffering HACE may experience amnesia, confusion, delusions, emotional disturbance, personality changes, and loss of consciousness. This acute high-altitude disease has long been known to cause brain damage. But one of the sobering things about the Fayed study is that none of the Everest climbers experienced high altitude cerebral edema, and the only acute case of mountain sickness was a mild one suffered by the expedition's amateur climber. Yet even all the professional mountaineers showed lasting brain damage -- presumably suffered on previous ascents to the high mountains, because their MRI scans were abnormal before the Mt. Everest ascent and unchanged after. How High is too High -- and Will It Get Better? Of course, Everest is extreme. What about ventures to lesser high altitudes? Fayed and colleagues also studied an eight-person team that attempted Aconcagua, a 6,926-meter summit in the Andes. Two climbers reached the summit, five ascended to 6000-6400 meters, and one reached 5500 meters. Yet three members experienced acute mountain sickness and two displayed symptoms of brain edema -- probably because they ascended more rapidly from lower altitudes than did the Everest climbers. All eight Aconcagua climbers showed cortical atrophy on MRI. Seven showed the enlarged Virchow-Robin spaces, and four showed numerous subcortical lesions. Some needed no brain scan to tell them their brains had been injured. One of the climbers suffered aphasia (problems with speech), from which he recovered 6 months later. Two complained of transient memory loss after returning, and three others struggled with bradypsychia (slowed mental function). The body is remarkably resilient--does the brain recover from these mountaineering wounds? To answer this important question, the researchers re-examined the same climbers three years after the expedition, with no other high-altitude climbing intervening. In all cases, the brain damage was still evident on the second brain scan. Still, Aconcagua is one of the world's highest mountains -- in the top 100. Mont Blanc, in the Alps, is less extreme. With a summit at 4810 meters, it is climbed each year by thousands of mountaineers who probably do not expect injury to their "second favorite organ," to use Woody Allen's nomenclature for the brain. Yet the researchers found that of seven climbers reaching the summit of Mount Blanc, two returned with enlarged VR spaces. Because Why? The study suggests that chronic exposure to high altitudes is not required to experience irreversible brain damage. In fact, amateurs seem to be at greater risk, since they are more likely to suffer acute mountain sickness or high-altitude cerebral edema. At the same time, the experience needed to become a well-acclimated professional seems to take its own toll; compared to the amateurs, however, the professional climbers in this study suffered greater cortical atrophy overall, which suggests an ever-increasing cumulative toll. Mountain climbing is growing in popularity, and with good reason. It can provide experiences of a lifetime; a communion with Nature and with friends that feeds the soul; intense and enduring rewards surpassing those found within the bounds of routine; and adventure and challenge that builds courage, stamina, and fortitude. It also gets you into incomparable mountain wilderness -- though that is vanishing under the transforming pressure of a warming, polluted atmosphere that is melting the alpine snows and under the repellent litter and human waste strewn along paths to even remote peaks. Sadly, many urgently sense that the singular "it" residing in George Mallory's pithy raison d'ascent, "Because it's there!", may soon be gone. Approximately 5000 climbers ascend Himalayan peaks every year, and many thousands more climb high in the Alps and Andes. Many spend huge sums to mount expeditions or pay enormous fees to be guided to the summit. This fascinating but sobering research by Fayed and colleagues makes it clear that these climbers are paying for the privilege with something more than hard-earned cash. They're paying with brain tissue.  R. Douglas Fields (shown here climbing the Nose of El Capitan in Yosemite) is a frequent contributor to Scientific American and Scientific American Mind and chief of the Nervous System Development and Plasticity Section at the National Institute of Child Health and Development, where he investigates neural development and the interactions between neurons and glia. -- Edited by David Dobbs at 11/30/2007 11:43 AM -- Edited by David Dobbs at 11/30/2007 11:43 AM

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