The investigators will conduct a non-randomized clinical trial to examine the effect of pure
oxygen breathing on the brain. The study will compare cerebral blood flow, cortical
electrical activity, and cognitive performance in 32 persons during room air (21% oxygen)
breathing and pure oxygen (100% oxygen) breathing. Subjects will be used as their own
controls. The investigators aim to:
1. Determine whether breathing 100% oxygen changes blood flow through the brain. The
investigators will learn whether brain blood flow is increased, decreased or stays the
same.
2. Determine if changes that might occur in brain blood flow are also accompanied by
changes in the brain's electrical activity (EEG).
3. Learn whether changes in the speed at which the brain processes information (cognitive
function) accompany changes in brain blood flow and electrical activity that may be
seen.