As context for anyone unfamiliar with the issue, below are some quotes from a 2008 SciAm article discussing a research paper by Fayed et al titled "Evidence of brain damage after high-altitude climbing by means of magnetic resonance imaging" (https://pubmed.ncbi.nlm.nih.gov/16443427/).

https://www.scientificamerican.com/article/brain-cells-into-... (emphasis added):

> … one of the sobering things about the Fayed study is that even when climbers showed no signs of acute sickness, the scans still found brain damage.

> The results in the Everest climbers were the starkest… The expedition had no major mishaps, and none of the 12 professional climbers evinced any obvious signs of high-altitude illness; the only acute case of mountain sickness was a mild one in the expedition’s amateur climber. Yet only one of the 13 climbers (a professional) returned with a normal brain scan. All the scans of the other 12 showed cortical atrophy or enlargement of the Virchow-Robin (VR) spaces. These spaces surround the 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 the young.

> The body is remarkably resilient: Does the brain recover from these mountaineering wounds? To answer this question, the researchers reexamined the same climbers three years after the expedition, with no other high-altitude climbing intervening. In all cases, the damage was still apparent on the second set of scans.