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Computers can crunch numbers indefinitely but after a few hours of steady brainwork, humans become logy, lose focus, and are given to impulsive behavior that brings quick rewards, like taking a break to play a video game or just zoning out.
Why does this happen?
Scientists have long told us that it’s similar to muscle work. Just as lifting weights wears out your muscles, heavy intellectual labor depletes the brain’s energy, they say. Eat some sugar and your brainpower will return, some even suggest.
Not so, researchers at Cambridge University found out.
The scientists began by looking at glutamate, the brain’s most abundant signaling biochemical and a key player in learning and memory.
Using a technique called magnetic resonance spectroscopy, the study team focused its attention on the brain’s lateral prefrontal cortex, which controls focus and planning. Mental exhaustion turns down activity here.
Study volunteers were divided into two groups.
One underwent a six-hour series of rapid, high-pressure mental tasks with only two ten-minute breaks and a quick lunch of a sandwich and piece of fruit.
The second group did the same tasks, but at a much more relaxed pace.
As the test went on, researchers found that glutamate levels among the first group rose by about 8 percent, while the second group showed no change in glutamate levels.
The researchers theorize that all that mental labor calls up an abnormally large amount of glutamate that floods the lateral prefrontal cortex and has a toxic effect.
Excess glutamate is known to cause brain malfunctions such as seizures.
Some brain specialists are skeptical, pointing out that even when excess glutamate builds up and we lose focus, we can still effortlessly recognize faces, which demands considerable mental wattage from the same part of the brain.
TRENDPOST: If brain fatigue is caused by glutamate building up as a waste product, the best-known way to clear waste from the brain is to sleep, which might explain why afternoon naps are so common and can help us power through the rest of the day.