OBJECTIVE: To assess whether fractional anisotropy (FA) values within white matter tracts or age had a significant factor in U-2 pilot neurocognitive performance.
INTRODUCTION: Previous research has demonstrated that high altitude U-2 pilots have decreased whole-brain average FA values, increased white matter hyperintensity (WMH) burden, and differences in neurocognitive function compared to other military personnel.  FA is a relevant imaging biomarker that can sensitively track white matter changes in neurological diseases and normal aging prior to development of WMH lesions. This analysis assessed whether FA values within white matter tracts or age had significant effect in U-2 pilot neurocognitive performance.  
METHODS: MRI and neurocognitive data were obtained from 103 U-2 pilots prior to implementation of the cabin altitude restriction effort (CARE). The CARE program modified the cabin altitude during flight operations above 21,000 m from approximately 9,000 m (28,000-30,000 ft) to approximately 4,500 m (15,000 ft).  FA values within multiple white matter tracts were acquired from diffusion tensor imaging (n=103). Neurocognitive data was attained through MicroCog evaluation (n=101). A generalized linear model was utilized to investigate independent effects of FA value and age on MicroCog metrics.
RESULTS: Higher FA values of the corpus callosum body, internal capsule, corona radiata, external capsule, and fronto-occipital tracts were independently associated with higher MicroCog Spatial Processing scores when controlling for age. Fronto-occipital tract FA values were significantly negatively associated with reaction time. Age was positively associated with reaction time across all tracts. 
CONCLUSION:   In our U2 pilot group both age and FA values independently influence certain microcognitive metrics with positive correlation to spatial processing when controlling for age in numerous tracts. Increasing age correlates with improved reaction time independent of FA values for all tracts. This study provides further insight that numerous white matter tracts are important in visual spatial integrity enhancing the concept that cortical function is emblematic of a diffuse network between brain regions rather than a discrete anatomical site.

Association of White Matter Integrity and Age on Cognitive Performance in U-2 Pilots

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