Do You Have an Average Brain? Its Unlikely.

When we are born, most organs in our body behave almost exactly as they will for the rest of our life. But not the brain. The brain, the organ responsible for our thoughts, emotions and behavior, instead evolves in an experience dependent manner after birth, developing its capability and function over our lifespan.

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The brain as the source of individuality

Unlike a computer, where the hardware can be identical but simply loaded with a personalized suite of software, the brain is a self-organizing and ever changing system of rippling electrochemical activity where it’s very structure evolves everyday. It is an organ constantly in flux, reorganizing and re-sculpting itself in response to your stimulus environment—the things you see, hear and touch. Practicing a musical instrument, carrying out your daily exercise routine or setting up long term cognitive habits can all reshape the neural networks of your brain and its patterns of activity. And since no two people have exactly the same experiences or behaviors, so you would expect that no two brains are exactly alike. Strangely though, we don’t tend to think of this individuality in terms of differences between brains.

Characterizing the average brain

As you must certainly have encountered, we often look to our DNA for differences that make us unique, yet our genes are 99.9% similar to one another. In contrast, neuroscientists have long sought to identify the ‘normal’ brain as the average of brains among us. The most common methodology in neuroscientific brain-imaging studies is to take the brain images from a particular group of people and average them together to create an impression of a “normal” brain for that group. This works for something like height, where someone who is average height would be considered ‘normal height’. Yet when it comes to the brain this average brain probably doesn’t actually exist in real life. In other words, these portraits of average brains which we see in research publications and media outlets correspond to no brain at all because every brain exhibits a pattern of activity that is slightly different from that average.

So when you read somewhere that on ‘average’ a specific part of the brain “lights up” when someone is thinking or doing something particular, it does not mean that yours necessarily will show that same pattern. Indeed, no surgeon would use a map of the ‘average’ brain to navigate your brain – the consequences could be disastrous. This is why patients are required to be awake during some forms of brain surgery, so that surgeons can poke and prod the brains of their patients and get verbal responses, just to find out what is going on with that part!

Brains and Cities

You could think about this practice of averaging brain maps as analogous to trying to understand a city by averaging together the maps of thirty different urban areas. All cities must have sections performing more or less the same functions but there are many ways for a city to do this, each adapted to its unique history and environment. Sure, the sewers are always underneath the city landscape (like brain stems) and Main street is somewhere in the middle, but the newspaper offices could be just about anywhere, and some cities have more than others. And what neuroscience has been showing us for some time is that the brain also works like this, at least in the “higher brain” or cortex – from where your personality and most of your abilities emerge.

The biggest fault in this city analogy is that most cities change a lot more slowly than your brain does. In other words, the disparity between an individual’s brain and an average brain is several fold greater than what you might see when averaging together city maps. And although brains do have more-or-less universal large-scale structures, we now know that they are so adaptable that even areas as seemingly single-purpose as the “visual cortex” can be used for other functions, as apparently happens in the brains of the blind. Musicians, polyglots, and athletes can also develop observable brain-differences that serve the heavy demands of their skills.

Who is average or normal?

In other words, everything that is unique about you must be reflected by the uniqueness of your brain, whether in structure or activity. We never ask who has 'average' DNA and our differences in DNA are far fewer than the differences that evolve over our lifespans. And as we all know just by looking inside ourselves, there are enough subtle dimensions of ability and personality to guarantee that you will never meet your true mind-clone! Who has the average brain then, and how do we define ‘normal’?