"Even professional chess players start making mistakes, typically after 4–5 hours in the game, which they would not make when well rested," the study authors write. "But our findings show that cognitive work results in a true functional alteration - accumulation of noxious substances - so fatigue would indeed be a signal that makes us stop working but for a different purpose: to preserve the integrity of brain functioning." "Influential theories suggested that fatigue is a sort of illusion cooked up by the brain to make us stop whatever we are doing and turn to a more gratifying activity," Mathias Pessiglione of Pitié-Salpêtrière University in France, lead author of the study, said in a press release. And this might be the human body's way of protecting itself from burnout. These byproducts are thought to adjust our decision-making and provoke us to stop thinking so very hard and gravitate toward more relaxing, low-stress activities. According to a study published Thursday in the journal Current Biology, prolonged, intense cognitive activity literally causes potentially toxic byproducts like an amino acid called glutamate to build up in our brains. This mushy brain sensation probably isn't merely in our heads. We call that feeling mental fatigue - it's not that we feel sleepy, exactly, yet our minds are weak and it becomes really hard to do any more complex reasoning than we already have. At the end of it all, you probably felt like you needed to dissociate from the world because your brain had turned to Jell-O. Other genes involved in transmitting glutamate signals, which help regulate mood, had increased activity in tame foxes, Pipes said.Recall a time you stared at your screen for 10 hours to finish a last-minute report for work, a 2,000-word essay on a book you never read, or any other sort of mental marathon. In people, genetic variants of GRM3 have been linked to schizophrenia, bipolar disorder and other mood disorders. In a different sort of analysis, Pipes discovered that all aggressive foxes carry one form of the GRM3 glutamate receptor gene, while a majority of the friendly foxes have a different variant of the gene. But only one gene for sensing serotonin had higher activity in the friendly animals. Tame foxes are known to have more serotonin in their brains. The team had expected to find changes in many genes involved in serotonin signaling, a process targeted by some popular antidepressants such as Prozac. Pipes speculated that tame animals’ lower levels of dopamine sensors might make them less anxious. For example, aggressive animals had increased activity of some genes for sensing dopamine. Pipes found that the activity of hundreds of genes in the two brain regions differed between the groups of affable and hostile foxes. The amygdala, a pair of almond-size regions on either side of the brain, helps process emotional information. The prefrontal cortex, an area at the front of the brain, is involved in decision making and in controlling social behavior, among other tasks. The team collected two brain parts, the prefrontal cortex and amygdala, from a dozen aggressive foxes and a dozen tame ones. Rather than search for changes in genes themselves, Pipes and her colleagues took an indirect approach, looking for differences in the activity of genes in the foxes’ brains. The foxes’ tame and aggressive behaviors are rooted in genetics, but scientists have not found DNA changes that account for the differences. The descendents of those foxes crouch, flatten their ears, growl, bare their teeth and lunge at people who approach their cages. Tom Reichner/ShutterstockĪt the same time, the scientists also bred the most aggressive foxes on the farms. A new study links those behavior changes to changes in brain chemicals. Taming silver foxes (shown) alters their behavior. Now, more than 50 years later, the foxes act like dogs, wagging their tails, jumping with excitement and leaping into the arms of caregivers for caresses. Each generation, the scientists picked the tamest animals to mate, creating ever friendlier foxes. Belyaev and his colleagues selected the least aggressive animals they could find at local fox farms and bred them. He bred silver foxes ( Vulpes vulpes), which are actually a type of red fox with white-tipped black fur. The foxes she worked with come from a long line started in 1959 when a Russian scientist named Dmitry Belyaev attempted to recreate dog domestication, but using foxes instead of wolves. Lenore Pipes of Cornell University presented the results May 10 at the Biology of Genomes conference. The finding could shed light on how the foxes’ genetic cousins, wolves, morphed into man’s best friend. – Taming foxes changes not only the animals’ behavior but also their brain chemistry, a new study shows.
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