 Using magnetic resonance imaging (MRI), the scientists discovered that people with sleep apnea have mammillary bodies that are about 20 percent smaller, particularly on the left side.One of the key investigators hypothesized that repeated drops in oxygen lead to the brain injury.Obstructive sleep apnea is associated with problems in daytime functioning, such as daytime sleepiness, motor vehicle crashes, psychological problems, decreased cognitive functioning, and reduced quality of life.