John Hawks Anthropology Weblog : 2007 09Hawks notes: "the altitude of Mont Blanc is substantially lower than the Everest base camp at 5500 meters."
.... 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.
Better imaging technologies now show that high altitude exertion will cause significant irreversible brain damage in many people, very high altitude extertion will damage all brains.