Greater brain volumes are activated when performing simple calculating tasks in persons accustomed to lower altitudes than those to higher altitudes.

Chronic exposure to a hypoxic environment results in a number of physiological changes such as cardiac arrhythmia and pulmonary edema. We hereby studied the variations in activation of brain areas during simple calculation tasks between individuals originating from different altitudes. Two groups of subjects, one from 1700 m above sea level (lowlanders) and the other one from at least 3000 m above sea level (highlanders), performed a simple calculation task by heart. The fMRI were taken and horizontal, sagittal, and coronal sections were analyzed to identify activated brain areas. Both lowlanders and highlanders performed the calculation task successfully. Horizontal sections revealed similar activated areas in the deep and anterior part of the right parietal lobe of both lowlanders and highlanders. In the highlanders, coronal and sagittal sections showed lower activities. Smaller brain volumes were activated in the highlanders as shown by the computer brain templates, with fewer total voxels recorded than in the lowlanders (P = 0.003). Computerized comparison of overall active brain regions between lowlanders and highlanders also revealed that smaller brain regions were activated. The results showed that while all subjects completed the task successfully, the highlanders did so using smaller brain regions than the lowlanders.