Neurodiversity: if you haven’t heard or read the word, you may have been on another planet for the past five years. The term is in, and those who want to be trendy are using the term liberally. The term has rapidly gained popularity in a short period of time and, especially in the world of autism, has become indispensable.
The term, coined in 1998 by Australian Judy Singer, refers to the uniqueness of each brain. Brains differ greatly from one another and each of us has a pièce unique. And that’s just as well. Imagine if we all had the same brain or at least a brain that perceives and understands the world in identical ways. That would be boring, because everyone would see, feel or think the same. Just as our planet benefits from biodiversity, neurodiversity offers many benefits to human society. Within the neurodiversity model, brains that are considered a-typical, such as those of people with autism or ADHD, are therefore viewed not as “disturbed” or “defective” but as one of the many possible variations that exist in how brains work. Variations that can enrich society.
People with autism, ADHD and all other classifications of so-called neurocognitive disorders are called neurodivergent people: people whose brains deviate from what you might call the typical brain. People with such a typical brain are then called neurotypicals.
That term was originally created by autistic activist Laura Tisoncik. She rebelled against the deficit model of autism and therefore created (also in 1998), partly as satire, partly as political action, the website: Institute for the Study of the Neurologically Typical (ISNT)[i] . On that website, Laura parodied the DSM criteria for autism and presented the diagnostic criteria for neurotypical disorder (including fictitious code 666.00). Her (funny) website was a success and especially very popular with other autistic ‘self-advocates’ who, like Laura, disagreed with the negative way people with autism were described. Years later, the term “neurotypical” was also picked up by others, professionals and scientists, and has since become commonplace.
But does this neurotypical exist? Does a neurotypical brain even exist?
Sometimes neurotypical is equated with “normal”. Scientists and philosophers have been pondering what is ‘normal’ for centuries and the only thing they agree on is this: what is normal is very relative, because time- and place-bound. What we see as normal or abnormal (or an abnormality or disorder) changes over time and is culture-specific. One of the strong examples of this is that until 1974, homosexuality was mentioned in the DSM and thus seen as a disorder, whereas now in most cultures it is quite normal for people of the same sex to have sex with each other.
Normality refers to what is the “norm”. Neurotypical people, then, are people whose brains work within the norm. But what is that norm? When is something “abnormal”? Science helps us here. A somewhat technical explanation to start with.
Just about most, if not all, human traits have a normal distribution (also known among statistic nerds as the famous bell-shaped Gauss curve). It looks like this, a bit like a fat bump.
When we measure human characteristics, such as height, intelligence, resting heart rate, BMI, the number of hairs per square centimeter of skin on your head, as well as, for example, the number of minutes people spend in the shower, we see these distributed as above. Based on all measurements, we can determine a mean and a standard deviation. For body height, the average for Belgian men is 178 cm and the standard deviation is 10 cm. In a normal distribution, slightly more than 2 out of 3 people are within 1 standard deviation of the mean. Specifically, 68.2% of Belgian men are between 168 and 188 cm tall. 95.45% of men are within 2 standard deviations and thus measure between 158 and 198 cm.
In science, one takes those 2 standard deviations as the limit for what is still the normal variation. The 5% or so that fall outside of that (2.2% very low score and 2.2% very high score) is considered a statistically significant deviation[ii]. This is how it is for intelligence, for example. A mean IQ is 100, the standard deviation is 15. Anyone who scores more than two standard deviations above the mean (+130), is considered “gifted”. And we speak of intellectual disability when the IQ is lower than two standard deviations from the mean, lower than 70 in other words. In a normal distribution, this affects about 2.2% of people, which corresponds to the average number of the prevalence of intellectual disability. Ditto for giftedness. So in terms of intelligence, together these are the 5% neurodivergent people, the people who deviate significantly from the “normal variation.
Whew, that was a bit technical, but we got through it.
We have now briefly looked at the statistics for general intelligence. But as you may know: a general IQ doesn’t say much. After all, there are different forms of intelligence. And we can measure all those forms separately. And since we can assume that they all have a normal distribution, we will see significantly high or low scores in 5% of the people each time. Of course, these are not always the same people. For example, the people who score extremely high on number intelligence are not necessarily the same people as these who score extremely high for visual spatial intelligence, or musical intelligence.
Not to mention all those other cognitive functions we can measure, such as imagination, cognitive flexibility, theory of mind, attention, impulse control, field independence, working memory, planning, episodic and semantic memory. On each of those functions, about 5% of people will be outside the normal variation.
And then we have to get back to the numbers. Suppose we measure the 10 cognitive functions listed above, the probability of falling outside the normal variation on at least one aspect is 42%[iii]. And there are more than 10 cognitive functions. One of the most widely used tests for executive functions (the D-KEFS) alone distinguishes 16 different executive functions. So we can assume that there are several dozen different neurocognitive functions at work in the human brain.
If we measure 25 neurocognitive functions, the probability of falling outside the “normal zone” on at least one test is almost 75%. With 50 tests it becomes 92% and with 100 tests 99.5%.
And then we haven’t even talked about all kinds of psychological characteristics that are not ‘cognitive’ but are also part of what our brain does, psychological factors such as sensitivity to stimuli, temperament, sense of humor, egocentricity, … If we also take these factors into account, then everyone falls outside the norm somewhere.
Conclusion: no single person scores within the norm on all brain functions. The neurotypical does not exist, and if there are neurotypicals, they are exceptional and for that reason alone neurodivergent, since the vast majority of people have a neuroprofile with at least one abnormality.
Thus, there is no such thing as a normal or typical brain. There is neurodiversity, though, because our brains, like our fingerprints, are unique. Surely we do not speak of a “normal” fingerprint and divergent fingerprints either. Or as the philosopher Hannah Arendt once put it, “We humans are all equal, in the sense that we are all different from each other and unique.
And again: draw the comparison with biodiversity: surely we do not speak of a typical plant and divergent plants, a typical tree and divergent trees. And then what would be a typical bird?[iv]
This is not to say that we cannot distinguish ‘groups’ or ‘classes’ within neurodiversity. People who show the same ‘extraordinary differences’ on one or more cognitive functions can be distinguished as a separate group. Thus, within psychiatry and neuroscience, classification systems have also emerged, just as in biology. And so we now know classifications such as autism, ADHD, dementia, dyslexia, etc. But these classifications are not necessarily a faithful reflection of reality, but a matter of mutual agreement. That is why well-known classification systems such as the DSM get a refresh every few years, in which the agreements are reviewed and revised if desired. Certainly when it comes to human behavior (and classification systems such as DSM use behavioral criteria), what is ‘typical’ and ‘normal’ on the one hand and what is ‘abnormal’ on the other, is not fixed but is very much context dependent[v].
If neurotypical were to exist at all, you would always have to ask the question: in what context? For example, social norms are very dependent on culture: in Ghana, for example, there are fixed rules for who you should greet first in a group. In other cultures this is not fixed. Ditto for communication: for example, there are major cultural differences in how direct communication may be.
There is undeniable neurodiversity. Accepting and appreciating that diversity is important, but distinguishing between neurodivergent and neurotypical provides little added value, in my view, in the pursuit of respect for diversity. Statistically, everyone is neurodivergent. And apart from that, currently within the various groups of so-called neurodivergent people, it is not clear who is/may be a member of the club and who does not belong. Autism, ADHD, dyslexia, Tourette’s: these are often mentioned, but intellectual disability and dementia are rarely, if ever, mentioned, even though they are also forms of neurodiversity. Neurodivergent versus neurotypical increasingly leads to polarization. That certainly does not contribute to respect for diversity. And that diversity should be the norm. Without that norm, no inclusion.
In short, it may make sense in certain contexts, such as clarifying what autism is, to talk about people with and people without autism or autistic and non-autistic people. Placing autism versus neurotypical makes no sense, because without context it is not clear what neurotypical is. In practice, then, it will mainly come down to looking at how a person deals with the unique challenges in his or her individual life and the common expectations in the context(s) in which that person lives. Because even within the group of people with autism, there is a lot of neurodiversity. We’re talking about a spectrum, right?
[i] https://erikengdahl.se/autism/isnt/index.html
[ii] For the nerds: yes, sometimes the significance instead of p < 0.05 is also set to 0.01.
[iii] In case you’re wondering where that figure came from. The formula to calculate the probability is 1-0.9510. The power refers to the number of independent tests, in this case 10.
[iv] If you want to read more about this: in “Autism as Context Blindness,” I wrote an entire chapter on “concepts” and the conclusion was that what people call “typical” is very slippery and vague. For example, when asked to “imagine a typical single man” people don’t spontaneously start thinking of the Pope as well, even though he is an unmistakable member of the club of male singles. And when asked to imagine a typical bird, people from Western Europe think of completely different birds than people from the Indonesian archipelago.
[v] In nature, it is no different. For example, in certain biotopes palm trees are the typical or most common species, in other biotopes they are the exception. Or when you think of Sweden, do you think mainly of palm trees?