Popular myth in and outside education: we only use 10% of our brain (no, we don’t)

I asked yesterday on Twitter if there are some more myths people want me to discuss on this blog, and the first answer I received by Jeroen Janssen was: ‘we only use 10% of our brain’, you can replace the percentage with every small figure.

It is quit a popular theory that we only use a small part of our brain. Sadly, it is a myth like the left and right brain theory proved wrong.

This myth is even so widespread, there is a Wikipedia page about it, let’s look at the reason why it’s wrong:

“Neurologist Barry Gordon describes the myth as laughably false, adding, “we use virtually every part of the brain, and that [most of] the brain is active almost all the time”. 

Neuroscientist Barry Beyerstein sets out seven kinds of evidence refuting the ten percent myth:

  • Studies of brain damage: If 90% of the brain is normally unused, then damage to these areas should not impair performance. Instead, there is almost no area of the brain that can be damaged without loss of abilities. Even slight damage to small areas of the brain can have profound effects.
  • Evolution: The brain is enormously costly to the rest of the body, in terms of oxygen and nutrient consumption. It can require up to 20% of the body’s energy—more than any other organ—despite making up only 2% of the human body by weight. If 90% of it were unnecessary, there would be a large survival advantage to humans with smaller, more efficient brains. If this were true, the process of natural selection would have eliminated the inefficient brains. By the same token, it is also highly unlikely that a brain with so much redundant matter would have evolved in the first place.
  • Brain imaging: Technologies such as Positron Emission Tomography (PET) and functional magnetic resonance imaging (fMRI) allow the activity of the living brain to be monitored. They reveal that even during sleep, all parts of the brain show some level of activity. Only in the case of serious damage does a brain have “silent” areas.
  • Localization of function: Rather than acting as a single mass, the brain has distinct regions for different kinds of information processing. Decades of research have gone into mapping functions onto areas of the brain, and no function-less areas have been found.
  • Microstructural analysis: In the single-unit recording technique, researchers insert a tiny electrode into the brain to monitor the activity of a single cell. If 90% of cells were unused, then this technique would have revealed that.
  • Neural disease: Brain cells that are not used have a tendency to degenerate. Hence if 90% of the brain were inactive, autopsy of adult brains would reveal large-scale degeneration.
  • Another evolutionary argument is that, given the historical risk of death in childbirth associated with the large brain size (and therefore skull size) of humans, there would be a strong selection pressure against such a large brain size if only 10% was actually in use.

In the October 27, 2010 episode of MythBusters, the hosts used magnetoencephalography and functional magnetic resonance imaging to scan the brain of someone attempting a complicated mental task. Finding that well over 10% was active at once, they declared the myth “busted”. If you want some more reading material on the myth, check this overview by Ben Radford.

I want to add something. A couple of months ago I was present at a debate of 2 neurologists and they also discussed this myth. They agreed that the typical brain scan one gets to see also keeps this image alive:

One could think that in this picture only one small part of the brain is active. This is not the case, because the scan checks which region becomes more active, the normal activity is first measured.

Other myths about the brain that are at least partly wrong and that we will discuss the next coming period, inspired by the OECD report “Understanding the Brain: The Birth of a Learning Science”:

  • “There is no time to lose as everything important about the brain is decided by the age of three.”
  • “There are critical periods when certain matters must be taught and learnt.”
  • “Let‟s face it – men and boys just have different brains from women and girls.”
  • “A young child‟s brain can only manage to learn one language at a time.”
  • “Improve your memory!”
  • “Learn while you sleep!”

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