Aug 27

What fraction of our brain do we use?

human-20424_640There is a long-standing “science myth” claiming that “we only use ten percent of our brain”.  The myth dates back many years, and rises and falls in popularity, but has recently been reinvigorated by the movie Lucy, where it is asserted by the authoritative voice of Morgan Freeman.  It has been debunked so many times that there’s no point in adding to the list, but there are a couple of issues that are still worth discussing:  First, how did the myth originate? Second, what portion of our brain’s capacity do we actually use?

Before getting into those questions, though, let me give a few pointers to useful things that other people have written:

How did the myth originate?

The origin of the story is not entirely clear, but here is the answer that seems most likely.  In 1936 Lowell Thomas, a famous broadcaster and journalist, wrote an introduction to Dale Carnegie’s famous book How to Win Friends and Influence People.  That introduction included this sentence: “Professor William James of Harvard used to say that the average man develops only ten percent of his latent mental ability.”  William James was a tremendously influential psychologist and philosopher, and a great proponent of the idea that people are capable of self-improvement.  However, he never, as far as anybody has been able to tell, actually stated a specific value of ten percent, at least in print.  Possibly he mentioned that value in a talk, of which he gave a great many; or possibly Lowell Thomas gave a falsely precise value on the basis of a vague memory.

Regardless of its origin, the propagation of the story is clearly due to people hearing it, thinking it is cool, and repeating it—often with some degree of variation.  Thus “ten percent of his latent mental ability” morphed into “ten percent of the brain”.  That seems to be an “attracting state”, which has persisted in popular culture for several decades.

I’ll leave the origin story there, but let me make note of one consequence.  The fact that the statement does not have a definite origin implies that it does not have a definite meaning.  The word “capacity”, as I will explain, has a range of meanings.  If a specific person had made the statement in a specific context, it would be possible to ask which meaning that person intended.  But because the statement arose organically, there is no rationale for selecting any one particular meaning as the correct meaning.

How much of our brain’s capacity do we actually use?

In order to answer this question we first need to understand what it means.  The easiest way to get at that is to ask the same question about a type of device that we understand better:  a computer.  Let me ask the question, then, about the laptop computer I am using to write this blog post.  What fraction of its capacity do I use?

The problem with that question is that it is quite ambiguous.  Here are some of the things that it might mean:

  1. Do I make use of all the components of the computer?  Are there any components that I never use?
  2. Do I make full use of the CPU?  That is, do I ever push the CPU to 100% of capacity?
  3. Do I make full use of the RAM memory?
  4. Do I make full use of the hard disk?
  5. Do I always make full use of the CPU?  If not, what is my average usage, and could it be made higher?
  6. Are the programs that run on the computer as efficient as they could possibly be?  How much more could the computer accomplish if the programs were written more efficiently?

These are only some of the questions that could be asked.  Since the brain is basically a biological computer—an information processing device implemented by neurons rather than transistors—we can ask the same sorts of questions about it.  Let me consider a few of them, and the extent to which we can answer them:

Question: Do we make use of all parts of our brain?  Are there portions that we never use?

Answer: There are numerous parts of the brain whose functions we don’t understand, but as far as we can tell, every part has a function, and every part is used at some time.

Question: Do we ever use our brains at maximum level?  That is, do we ever get as much thought out of our brains as they are capable of generating?

Answer: It’s hard to say, and certainly there are times when we don’t feel that we are using our brains particularly effectively, for example, when we are sleepy.  But would it be possible to take our best thinking and ramp it up by a factor of ten?  There’s no reason to believe that anything like that is on the cards.

Question: Do we use our brains at maximum level overall?  That is, do we get as much thought out of our brains as possible over the course of a day?

Answer: Probably not, and it seems likely that there are things we can do to make our thought processes more effective.  These include exercise and nutrition, but also possibly activities such as playing video games or doing “brain fitness” training.  Clearly we can increase our brain productivity for a limited time using drugs such as caffeine or amphetamines.

Question: Do we use our brain’s memory capacity as effectively as possible?

Answer: In spite of the plethora of “memory training” techniques that are advertised, there is little evidence that any of them are very useful in real life.

Question: Could we use our brains better by thinking more efficiently?

Answer: This seems like the area where there is the greatest room for improvement.  “Thinking more efficiently” basically means learning, and it’s hard to put bounds on how much the productivity of our minds can be improved by learning.


Here’s the bottom line: our brain has lots of different capacities, and many of them can probably be improved to some degree.  But there is no justification for applying a figure of “ten percent” to any of them.  That’s pure mythology, and ought not to be propagated.

Older posts «