As a neuroscientist with a focus on cognitive functions and the effects of physiological states on the brain, I can tell you that dehydration can have significant effects on brain function. When you're dehydrated, your brain doesn't function as efficiently as it should.

Firstly, dehydration can lead to a decrease in cognitive performance. This is because the brain tissue is about 75% water, and even mild dehydration can impair concentration and short-term memory.

Secondly, dehydration can cause headaches and migraines. This is likely due to the fact that water is crucial for the proper functioning of the brain and the removal of toxins. When you're dehydrated, your brain can swell, leading to pain.

Thirdly, there's an increased risk of fatigue. Water is necessary for the production of energy in the body, and without it, you may feel sluggish and tired.

Fourthly, dehydration can affect your mood. Studies have shown that even mild dehydration can lead to mood disturbances such as anxiety, depression, and irritability.

Lastly, severe dehydration can lead to delirium and confusion. This is a serious condition that requires immediate medical attention.

It's important to stay hydrated, especially during hot weather, after exercise, or when ill, to maintain optimal brain function.

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By the time you feel thirsty your body is already dehydrated; our thirst mechanism lags behind our actual level of hydration. ... Data in humans is lacking and contradictory, but it appears that brain tissue fluid decreases with dehydration, thus reducing brain volume and temporarily affecting cell function.read more >>