Happy new year everyone!

Like many of us, I have been thinking about my new years resolutions and goals for 2022. Whilst looking for inspiration for resolutions online, I noticed lots of websites and youtube videos recommending personality tests to identify areas of strengths and weaknesses. One of these tests I stumbled upon was the ‘left brain / right brain’ test.

These quizzes asked various questions and then told you whether you were predominantly ‘left brained’ or ‘right brained’. I thought this was fascinating! Is it really possible to divide people into two groups based on their personalities? And are these personality traits connected to different sides of the brain? To find out more, we asked 5 experts in neuroscience and psychology, “Are people predominantly either ‘left-brained’ or ‘right-brained’?”, here is what they said…

EXPERT CONSENSUS

Are people predominantly either 'left-brained' or 'right-brained'?

100% ‘No’ based on 5 expert responses

What is the ‘left brain/right brain’ theory?

The left brain/right brain theory initially inspired by a neuroscientist called Roger Wolcott Sperry in 1960. Sperry carried out ‘split brain experiments’ on patients who lacked normal connections between the left and right sides (also called hemispheres) of their brains. The right brain hemisphere is connected to the left side of the body, whilst the left brain hemisphere is connected to the right side of the body. This meant that, by covering one eye and showing images or words to a patient with a split brain, Sperry could compare how the left and right hemispheres of the brain described the images and words. Interestingly, these experiments found that, in these patients whose left and right hemispheres are not connected, the two sides of the brain worked independently. The left hemisphere used language to describe what they saw, whilst the right hemisphere could draw.

Since these differences between the left and right hemispheres of the brain were discovered, many have exaggerated and over-interpreted Sperry’s findings. Now, the left brain/right brain theory is that people can be categorised as ‘left brainers’ or ‘right brainers’ based on which side of the brain is more dominant. Most websites or online quizzes that describe the left/right brain theory will list a whole range of characteristics that can be linked to these two categories. These include emotional intelligence, creativity and spontaneity for ‘right brainers’ and critical thinking, maths and planning for ‘left brainers’. Some sites even suggest that you pursue certain careers based on which category you fall under.

What is the evidence that people are ‘left-brained’ or ‘right-brained’?

All 5 experts agreed that people are not predominantly ‘left-brained’ or ‘right-brained’. Dr Jean-Francois Delvenne, an expert in neuroscience and psychology from Leeds University in the UK, says “This is another popular myth that is not supported by scientific evidence. Human society is built around categories, and there's something seductively simple about classifying people as either analytical left-brainers or a creative right brainers.”

In 2013, a group of researchers in Utah, USA, analysed magnetic resonance imaging data from 1011 people’s brains. They found that, although brain activity varied across all the people in the dataset, there was no evidence that some people used one half of their brain more than the other half. Dr Nils Rosjat, an expert in computational neurobiology from the Jülich research centre in Germany, says “There is no evidence, that a ‘domination’ of one hemisphere leads to a more creative or a more logical ability.”

What differences are there between the left and right sides of the brain?

There is evidence, such as from the split-brain experiments, that some functions are performed by different parts of the brain. This is called ‘lateralisation of brain function’. Dr Delvenne says “For most people, for example, language is largely localised to the left hemisphere, while spatial processing is predominantly localised to the right hemisphere. Those discoveries of hemispheric lateralisation have most likely led to the left-brain right-brain idea.”

The differences between the left and right hemispheres of the brain are not always obvious. Dr Delvenne says “the brain is not as clear-cut as the myth makes it out to be. For example, the right hemisphere is also involved in processing some aspects of language, such as intonation and emphasis.”

Importantly, we always make use both sides of our brains. Dr Delvenne says “The two hemispheres are interconnected by a large structure called the corpus callosum. They work together constantly to produce one consciousness. There simply is currently no evidence in neuroscience for lateralisation of human personality style.” Dr Rosjat agrees, “Both hemispheres need to work together.”

The takeaway:

People are not predominantly ‘left-brained’ or ‘right-brained’. Most tasks require us to use both sides of our brain together.

May the facts be with you!

Eva

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