Why thinking too much is literally poisonous

By Gwyn Wright via SWNS

Too much thinking is literally poisonous and mental fatigue allows our brains to clear toxins produced by thought, according to a new study.

Scientists say thinking hard for a long time releases noxious substances in the prefrontal cortex at the front of our brains.

This changes how people control their decisions and they move towards easier actions requiring no effort or waiting.

Earlier research has suggested tiredness is a type of illusion cooked up by the brain so we stop what we are doing and do something more fun or gratifying.

The French researchers wanted to understand why machines can compute continuously but our brains cannot, but were skeptical of earlier explanations for this.

They suspected it had something to do with the brain’s need to recycle substances, which can be toxic, that arise from thinking.

For the study, the team used magnetic resonance spectroscopy- a type of brain imaging- to study people’s brains during a typical workday.

They looked at people who needed to think hard and others who were given easier tasks.

Signs of fatigue, including reduced pupil dilation, were found only in the group doing hard work.

As the hard workers became tired they became keener on tasks that required less effort and a short delay in getting a result.

They also had higher levels of glutamate, which the team says causes fatigue, in synapses of the brain’s prefrontal cortex.

The team says the findings suggest too much glutamate makes further activation of the brain more costly and controlling it becomes harder after a mentally tough workday.

The authors say people should avoid making important decisions when tired and that workplaces should make sure their employees don’t burn out.

Metabolites in our brains could also be monitored to avoid severe fatigue.

Study author Mathias Pessiglione from Pitié-Salpêtrière University in Paris said: “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.

“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.”

He adds that there is no magic cure for tiredness.

He said: “I would employ good old recipes: rest and sleep. There is good evidence that glutamate is eliminated from synapses during sleep.”

The authors now want to look at whether the same markers of fatigue in the brain may predict recovery from health conditions, such as depression or cancer.

The findings were published in the journal Current Biology.