I naively assumed this was true for everyone but I just found an intriguing 1996 study that compared brain function of lowland mountain climbers and Nepalese Sherpas after ascent to high altitude, which found that the Sherpas suffer few of these neurological problems.
Are Himalayan Sherpas better protected against brain damage associated with extreme altitude climbs?
Garrido E, Segura R, Capdevila A, Pujol J, Javierre C, Ventura JL.
Clin Sci (Lond). 1996 Jan;90(1):81-5.
1. The potential risk of brain damage when low-landers attempt to climb the highest summits is a well-known fact. However, very little is known about what occurs to Himalayan natives, perfectly adapted to high altitude, when performing the same type of activity.
2. Taking into account their long-life climbing experience at extreme altitudes, we examined seven of the most recognized Sherpas with the aim of performing a comprehensive neurological evaluation based on medical history, physical examination and magnetic resonance brain imaging. We compared them with one group of 21 lowland elite climbers who had ascended to altitudes of over 8000 m, and another control group of 21 healthy individuals who had never been exposed to high altitude.
3. While all of the lowland climbers presented psychoneurological symptoms during or after the expeditions, and 13 of them (61%) showed magnetic resonance abnormalities (signs of mild cortical atrophy and/or periventricular high-intensity signal areas in the white matter), only one Sherpa (14%) showed similar changes in the scans, presenting neurological symptoms at extreme altitude. The neurological examination was normal in all three groups, and no neuroimaging abnormalities were detected in the control group.
4. The significant differences, in both clinical and neuroimaging terms, suggest that Sherpa highlanders have better brain protection when exposed to extreme altitude. Although the key to protection against cerebral hypoxia cannot be established, it is possible that an increase in the usually short period of acclimatization could minimize brain damage in those low-landers who attempt the highest summits without supplementary oxygen.
Link to study of neurology of lowland climbers and Sherpas.