New research shows your brain swells when you are dehydrated and your ability to perform routine tasks is diminished. Those are the findings of a group of exercise physiologists from Georgia Tech.

A group of volunteers was put through a series of tasks and observers saw changes inside the brain and recorded diminished results as a result of dehydration. The volunteers did not perform as well even when exerting themselves in the heat while staying hydrated but the loss of water caused their performance to suffer all the more.

"We wanted to tease out whether exercise and heat stress alone have an impact on your cognitive function and study the effect of dehydration on top of that," said Georgia Tech’s Mindy Millard-Stafford. "We found a two-step decline."

Researchers were looking to determine how people affected by dehydration might react to performing repetitive tasks because of the implications for occupational safety, military readiness and competitive athletic performance.

"When I was just getting interested in this subject, my brother was doing an internship at a steel plant, where I visited him, and it was extremely hot," said study author Matt Wittbrodt. "In addition, everyone had on layers of protective clothing. We want to figure out if we can help prevent accidents in those environments."

During experimentation the volunteers were asked to complete repetitive, mindless tasks in states of total relaxation, exertion with hydration and exertion without hydration. Brain scans showed when the participants were hydrated the ventricles in the center of their brains contracted and during periods of dehydration they expanded. However, that condition seemed independent of the slump in performance which was attributed to changes in neural firing patterns that showed up during dehydration.

"The areas in the brain required for doing the task appeared to activate more intensely than before, and also, areas lit up that were not necessarily involved in completing the task," Wittbrodt said. "We think the latter may be in response to the physiological state: the body signaling, 'I'm dehydrated'."

Researchers now want to look into how sports drinks compare to water in such situations because too much water is not good either.

"Blood plasma gets diluted with water replacement alone," Millard-Stafford said. "If blood sodium—plain old salt—drops too much while water in the blood increases too much, that's dangerous. It's a condition known as water intoxication or hyponatremia."

Click here to read more in the journal Physiological Reports.