That Thinking Feeling

Psychology's answers to everyday questions, in blog form!

Are there really left-brained and right-brained people?

Greetings, fellow humans. I am wearing socks that say KAPOW! and I am ready to tell you about psychology. This question is courtesy of someone who wishes to be known only as An Interested Reader from the North.

I think most people have heard the idea that there are left-brained people and right-brained people at some point or another. If you haven’t, here’s a quick run-down of the theory: just like most people have a dominant hand that they do most tasks with, they also have a dominant side of the brain that they do most tasks with. Right-brained people tend to be creative and intuitive, and left-brained people are logical and analytical.

 
‘Logical’ left and ‘creative;’ right brain drawing

‘Logical’ left and ‘creative;’ right brain drawing

 

Is it true? Not really.

The thing is, brains do something called hemispheric lateralization, which means that the hemispheres (left and right sides) of your brain don’t divide up tasks equally – some tasks largely happen in one hemisphere, and some largely happen in another [i].

Human brains typically do most of the processing of language in the left side and may process emotions mostly on the right side or perhaps different emotions on different sides (you might remember this from an earlier blog of mine on selfies). Interestingly, it’s not just human brains that do this; when a frog croaks, the left side of its froggy brain is doing more of the work than the right side. However, even if a frog is really good at croaking, that doesn’t mean it’s a ‘left-brained’ frog. Similarly, a human who is really good at emotions is not ‘right-brained’.

The source of the myth is probably some experiments done in the 1960s [ii]. The researchers doing these experiments looked at the way people processed information after they had had surgery that separates the two hemispheres of the brain.

Why would you want to separate the hemispheres? Because of epilepsy.

Having an epileptic seizure is almost like having a wildfire in your brain. The seizure can start at one point in your brain and spread from there, eventually causing you to lose consciousness. These seizures are temporary but also dangerous as it’s usually not possible to predict when one is going to happen. For many people, seizures can be treated with medication. For those who don’t respond to medication and who have very severe seizures, one option is to sever the pathway joining the two halves of the brain (in yellow below – the picture shows the brain as you would see it if you sliced it across horizontally about halfway down). This area, the corpus callosum, joins the left and right halves of the brain together. Cutting it prevents the seizure from spreading between halves of the brain, and surprisingly has relatively few side effects, so the benefits are considered to outweigh the costs.

 
Corpus callosum diagram from Gray’s  Anatomy  (public domain)

Corpus callosum diagram from Gray’s Anatomy (public domain)

 

 

One of the side effects is that the two sides of the brain don’t share information any more. Usually, this isn’t a problem – the two halves of the brain are getting the same inputs from the world, they just deal with them separately. However, it’s possible to present things to only one half of the brain by presenting them in one half of the visual field (that is, not to one eye but so that they are only visible in one half of each eye). If you do this with people who have had their corpus callosum severed, then you see some interesting effects. For example, if you show an instruction only to the left side of the brain, the person will be able to follow it – but not if you only show it to the right side. This isn’t the case with a person who hasn’t had the operation: the right brain and the left brain share information and work together, neither one dominating the other.

Now that we know the right-brained/left-brained myth is not true, there’s one thing left to do. A 2012 study [iii] found that over 90% of teachers in the UK and over 80% of teachers in the Netherlands believe the statement, “Differences in hemispheric dominance (left brain, right brain) can help explain individual differences amongst learners.” I don’t say this to blame teachers; as we have just seen, it is very easy to draw that conclusion from studies on hemispheric lateralization. However, myths like this can make the job of a teacher much harder. So, if you are a teacher, tell your colleagues, and if you know a teacher, please forward this on to them!

 

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