Have you ever had a long few hours of mental work and felt completely worn out after? Researchers say there might be something to this. A recent study published in Current Biology found that “when intense cognitive work is prolonged for several hours, it causes potentially toxic byproducts to build up in the part of the brain known as the prefrontal cortex. This, in turn, alters your control over decisions, so you shift toward low-cost actions requiring no effort or waiting as cognitive fatigue sets in”. This was discovered through the use of magnetic resonance spectroscopy which monitors “brain chemistry over the course of a workday.” The group of participants doing hard work showed signs of fatigue, reduced pupil dilation, and a shift in their choices “toward options proposing rewards at short delay with little effort.” The researchers also found higher levels of glutamate in synapses of the brain’s prefrontal cortex in this group. The researcher’s advice? Rest and sleep! “There is good evidence that glutamate is eliminated from synapses during sleep.”