It goes without saying that the body is designed to work aerobically. The mind therefore, follows the same pattern. This essay by Rodway shows historical data and research about the changes in cognition as one goes further up into thin air. This is important, because they conjecture that many of the problems climbers face are so serious that they have life or death implications, and thus the brain cannot process them as it should, leading to fatal errors.
“Mountaineers have often observed a lack of clarity in their mental state at high altitudes; it is difficult for the stupid mind to observe how stupid it is.” George Leigh Mallory 1922
He further explains how this is likely a combination of sleeplessness due to periodic breathing as well as hypoxia due to the altitude. Interestingly, one of the references (Richalet) showed that psychomotor performance and mental efficiency declined progressively with altitudes above 5500m, but differences did not reach statistical significance until 8000m. Another reference (Waters) in the same paper describes the neuropsychological effects of sleep loss. They include: sleep loss effects both cognitive functions as well brain regions that support cognitive performance; decreased processing speed is most reliable finding after sleep loss; and peformance decreases appear in a dose dependent manner with sleep debt accumulation.
Thus, be aware (and self aware as best as possible) to the problems associated with cognitive function with high altitude climbing. You wouldn’t let a drunk drive you home, don’t let one hold the rope that keeps you alive.
“Decision making at extreme altitude: Has anyone seen my executive function lately?”