Speech production and cognitive deficits on Mt. Everest

Deficits in speech motor control and in the comprehension of syntax were observed as five members of the 1993 American Sagarmatha Expedition ascended Mt. Everest. We analyzed speech recordings and cognitive test scores of the climbers at different altitudes. The mean "voice onset time" interval that differentiates "voiced" stop consonants from their "unvoiced" counterparts (e.g., a [b] from a [p]) decreased from 24.0 ms at Base Camp to 5.4 ms at Camp Three. The time needed to comprehend simple spoken English sentences increased by 50% at higher altitudes, and was correlated with speech motor deterioration. This pattern of deficits is similar to that noted for Parkinson's disease and may reflect disruption of subcortical pathways to prefrontal cortex. Similar procedures could be used to remotely assess cognitive impairments caused by hypoxia, carbon monoxide or alcohol intoxication, or drugs, in order to monitor crew behavior in aeronautics and spaceflight operations, or to evaluate the treatment of neurodegenerative diseases such as Parkinson's disease.