Friday evening had a familiar vibe. After a long day of work, you and your buddies finally decide where to meet for a night out.
However, by the time you’ve worked out what to wear and where you left your keys, a night on the couch seems preferable to a night on the dance floor.
Now, scientists believe they may be able to explain why you feel so exhausted before reaching the bus stop: your brain has slowed down in response to the stress.
The brain may experience a condition similar to the unpleasant accumulation of lactate in exercising muscles. This may explain why mental labor and resisting the impulse to quit throughout the day feel equally difficult.
According to a study published in Current Biology, prolonged mental activity leads to the accumulation of a potentially hazardous neurotransmitter in the prefrontal cortex. The researchers propose that the brain slows down its activity to handle the buildup, explaining why we feel exhausted.
“Even when you resist scratching an itch, for instance, your brain is exercising cognitive control,” said the study’s lead author, Antonius Wiehler of the Paris Brain Institute. According to him, repeated demands on cognitive control processes might result in tiredness.
The prefrontal cortex is the region responsible for decision-making and cognitive control, which are utilized when the brain resists an impulse or any temptation.
The researchers studied the brain chemistry of forty volunteers as they performed repetitive computer tasks. They divided into two groups, each performing either difficult or simple tasks for almost six hours.
The levels of a neurotransmitter in the prefrontal cortex were tested by the researchers. They discovered a larger buildup of glutamate in subjects assigned more difficult tasks.
Thinking-intensive work demands the brain to continually reject the impulse to pursue something less challenging. Unsurprisingly, this can result in fatigue, although the underlying brain chemistry remains unknown.
Now, researchers hypothesize that cognitive control may lead to the accumulation of glutamate in the brain – a neurotransmitter whose overexcitation of neuronal cells might be hazardous.
Wiehler stated, “We discovered that glutamate accumulates in the region of the brain that regulates the activities we assign to participants.” “According to our knowledge, the brain has some type of clearing system to prevent this, which may reduce activity.”
Mental tiredness may be connected to the recycling of glutamate that accumulates during brain activity, according to the study. “The accumulating glutamate must be eliminated, which we believe occurs during sleep,” Wiehler explained.
When participants were asked to indicate their level of weariness, no conclusive link between glutamate and fatigue was discovered – groups performing difficult and easy activities reported the same amount of fatigue. This could be owing to the subjective nature of exhaustion and the fact that those performing the simple activity were unaware of the difficulties of the other.
Dr. Anna Kuppuswamy of the Institute of Neurology at University College London, who was not involved in the study, said, “The fact that glutamate levels do not correlate with self-reported fatigue is somewhat disappointing, but not surprising, as there is often a dissociation between biological features and self-reported fatigue.”
The researchers analyzed only glutamate, but they speculate that other related chemicals may be associated with exhaustion. “The study analyses a particular neurotransmitter in a very specific region of the brain, so we need to take a broader view,” Kuppuswamy explained.
She stated that the results were however encouraging. “We know that during exercise lactate accumulates in the muscles, causing muscle exhaustion. It is rather obvious that a comparable process occurs in the brain, and this is good preliminary evidence to support that notion.”
