How Thinking Tires the Brain

By Shlomo Maital

    Ever feel tired, just from sitting around and thinking hard?  Now comes a scientific breakthrough, beautifully reported by The Economist (August 22).

     A team of scientists led by Antonius Wiehler of Pitié-Salpêtrière University Hospital, in Paris, hypothesize that cognitive fatigue results from an accumulation of a certain chemical in the region of the brain underpinning control. That substance, glutamate, is an excitatory neurotransmitter that abounds in the central nervous systems of mammals and plays a role in a multitude of activities, such as learning, memory and the sleep-wake cycle.

    In other words, cognitive work results in chemical changes in the brain, which present behaviorally as fatigue. This, therefore, is a signal to stop working in order to restore balance to the brain.

     But —  how did the researchers discover this?  They did a neat experiment:

     To induce cognitive fatigue, a group of participants were asked to perform just over six hours of various tasks that involve thinking. Half were assigned easy things to do and half hard ones. For example, in one task, letters were displayed on a computer screen every second or so. Those in the easy group had to remember whether the current letter matched the previous letter or, for the hard group, the one shown three letters earlier.

    What did they find?

   “During the experiment the scientists used a technique called magnetic-resonance spectroscopy to measure biochemical changes in the brain. In particular, they focused on the lateral prefrontal cortex, a region of the brain associated with cognitive control. If their hypothesis was to hold, there would be a measurable chemical difference between the brains of hard- and easy-task participants. And indeed, that is what they found. Their analysis indicated higher concentrations of glutamate in the synapses of a hard-task participant’s lateral prefrontal cortex. Thus showing cognitive fatigue is associated with increased glutamate in the prefrontal cortex.”

 So, my friends.  If you have spent hours working on an idea, writing something, thinking hard, planning —  your brain tires.  Doesn’t help to push on.  Rest.  Your prefrontal cortex is where ideas are born.  Give it a break.  Give the brain time to get rid of all that glutamate.  It’s like lactic acid that accumulates in your muscles toward the end of a long run.