Posted by 
Dehydration causes neural signaling and conspicuous changes in the brain, making it difficult to do monotonous tasks. Physiologists at the Georgia Institute of Technology studied volunteer subjects who sweated a lot and did not hydrate. The fluid loss led most of the subjects to make more goofs on the task, and areas of participants’ brains showed conspicuous changes.
When study participants exercised, sweated and drank water, fluid-filled spaces called ventricles in the center of their brains contracted. But with exertion plus dehydration, the ventricles did the opposite; they expanded. Functional magnetic resonance imaging (fMRI) revealed the differences. Oddly, the ventricle expansion in dehydrated test subjects may not have had much to do with their deeper slumps in task performance.
Changes in neural firing patterns 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. Past studies have indicated that this kind of task reflects the neural processing involved in real-life motor functioning, especially in the repetition common in manual labor or military exercises. Such monotony can foster attention lapses that heat, strain, and fluid loss may exacerbate.
Thirteen volunteers performed the task on three separate occasions: once after just relaxing and staying hydrated, after extended heat, exertion, and sweat but with drinking water during exercise, and once with heat, exertion, and sweat but without drinking water. After relaxing, task performance gradually slipped as the 20 minutes crept by. But under the subsequent stressors, average overall performance ratcheted down. A few of the volunteers did perform the task stalwartly under all imposed conditions.
The subjects completed the task in air-conditioned rooms and after a break from strenuous activity. In a real-world scenario, in which heat and toil are unrelenting, performance may collapse even further. Blood plasma gets diluted with water replacement alone, if blood sodium drops too much while water in the blood increases too much, that’s dangerous. It’s a condition known as water intoxication or hyponatremia.