I wonder HOW deprived of O2 the brain needs to be for stuff like this
to happen--if it is happening. Perhaps at some point in the future
keeping people (ahem) at hemoglobin levels of around 10 for 72 weeks
will be considered...ill advised...

October 20, 2008, 1:06 pm

Mountain Climbing Bad for the Brain

By Tara Parker-Pope

High-altitude climbing can damage the brain. (Tony Smith/The New York
Times)

If you’ve ever fantasized about scaling Mount Everest, think again. A
new study of professional mountain climbers shows that high-altitude
climbing causes a subtle loss of brain cells and motor function.

Italian researchers used magnetic resonance imaging to look at the
brains of nine world-class mountain climbers who had at least 10 years
of experience, including expeditions to Mount Everest and K2. The
climbers ranged in age from 31 to 52, with an average age of just
under 38, and were used to climbing to altitudes of at least 4,000
meters (two-and-a-half miles, or over 13,000 feet) several times a
year.

The scientists, who published their findings in the October issue of
the European Journal of Neurology, compared the climbers’ M.R.I. brain
scans with 19 age- and sex-matched healthy control subjects. A number
of neuropsychological tests were also carried out to assess the
climbers’ cognitive abilities, including memory and motor functions.

On scans, the climbers showed a reduction in both white and gray
matter in various parts of the brain. Overall, the researchers found
that the cognitive abilities that were most likely to be affected were
the climbers’ executive function and memory.

Six of the nine climbers had lower than average scores on the Digit
Symbol test, which measures executive functions. Three out of nine
scored lower than average on memory tests, while four scored below
average on a visual-motor function test. The study authors noted that
the results “are most likely to be due to progressive, subtle brain
insults caused by repeated high-altitude exposure.”

Other studies have shown links between brain problems and repeated
exposure to extreme conditions. The British Journal of Sports Medicine
reported in 2004 that scuba diving may have long-term negative effects
on the brain, particularly when performed in extreme conditions, such
as cold water, more than 100 dives per year, and diving below 40
meters.

And last year, researchers at New York University noted that high-
altitude illness is a growing concern in sports medicine given the
increasing popularity of extreme sports like high-altitude
mountaineering, skiing and snowboarding. The report noted that about
20 percent of tourists to Colorado report acute mountain sickness, and
complications arising from sports activities at high altitudes, such
as the potentially fatal conditions of pulmonary and cerebral edema,
are on the rise.