Why the notion of having a dominant hemisphere in your brain is nonsense
What sort of thinker are you? If you describe yourself as left brain instead of logical, analytical, or rational, or right brain, instead of creative, intuitive, or emotional then you’ve fallen for a long held, but completely erroneous neuromyth — the myth of hemispheric dominance.
This myth, which is sometimes called the left-brain, right-brain dominance theory, claims that how people think about things is due to one side of the brain being more dominant than the other. If you think in words or solve problems logically, then, the pseudoscience goes, your left hemisphere is more dominant than your right. If you are good at finding patterns or feeling your way to an answer, your right brain is calling the shots.
Whilst there is no doubt people have different cognitive styles, preferences, and skills, there is no evidence to suggest that this relates one side of your brain being more dominant than the other. It is not the way the brain works.
Or, to quote Professor of Neuroscience, Dr Mark Williams, “It is complete nonsense.”
Despite this, a vast industry has sprung up around incorrectly linking cognitive styles with hemispheric dominance, and it is unfortunately prolific in both educational and corporate settings. Books and programmes promote whole brain training as a way to strengthen or “balance” the hemispheres. Educational efforts are directed to deliver content that matches different hemispheric leanings. Leadership courses promote management styles to get the best out of left or right brain employees. Psychologists themselves are known to promote the erroneous idea of left or right brain dominance.
Like all neuromyths, this one has its roots in nuggets of fact, but its claims have extended far beyond the reality.
The human brain consists of around 100 billion neurons and around 100 trillion connections. Like much of our bilaterally symmetric body — with our two legs, two kidneys, two ears and so on, our brain also consists of two sides, one on each side of our midline. These separate hemispheres communicate with each other via a thick tract of connecting axons called the corpus callosum. However, even though we might have a dominant hand, this is not true for the brain. Although perhaps this is why people can easily believe that the brain must also have a dominant side.
Even though both sides of the brain are not mirror images of each other, they have many similar functions. They process and integrate sensory information and issue motor commands, for example. Different parts of the brain differentially process specific types of information and are therefore more involved in particular tasks or functions than others. The back part of both sides of the cerebral cortex, the occipital lobe, processes different types of visual information. On the other hand, planning and executing voluntary movements is under the control of clusters of neurons towards the front of our heads — in the frontal lobe.
There is a hemispheric difference here in that each side of the brain is responsible for one side of the body — the opposite side. The right hemisphere controls, and receives feedback from, the left side of the body. The left hemisphere does this job for the right side of the body. But, provided you’ve learnt to crawl, they work seamlessly together. We can clap our hands, scratch an itchy spot on our left knee with our right hand and execute complicated moves on the dance floor using both sides of the body without any problems at all.
Perhaps for reasons of efficiency, there are a number of higher order functions that are lateralised to one side of the brain, rather than the other.
This means that when the brain is involved in a specific task there is more activity in one hemisphere compared to the other. This does not mean this part of the brain is more dominant than another part. It just means this is where the processing of that particular type of information happens.
Perhaps the most famous and oldest known lateralisation is language. In most people, the language centres of the brain are situated in the left hemisphere, although this is not always the case. Approximately 95% of right handers, and 75% of left handers have language lateralised on the left, but in other people it could be right lateralised, or bi-lateral
– spread across both hemispheres.
Going all the way back to the 1860s, Paul Broca was one of the first scientists to provide definitive proof that specific parts of the brain are responsible for different functions. He studied, and later dissected, the brains of stroke victims who lost the power of speech. He showed that they had damage in similar areas of the left hemisphere of their brains. Later work by Roger Sperry and Michael Gazzaniga with split brain patients, epilepsy sufferers who had their corpus callosum severed such that the left and right hemispheres could not communicate, reconfirmed this.
Roger Sperry and his colleagues went further. Utilising the fact that the left visual field sends information to the right hemisphere (and in split brain patients, only the right hemisphere), and vice versa, they conducted a variety of quite fascinating experiments on split-brain patients. In addition to observing that the right hemisphere was mostly silent, they found evidence to indicate it was better at tasks involving processing of spatial information, pattern recognition and dealing with emotional content. In addition to being the home of language, they claimed the left was better at logical problem solving and rationality. The claim was made that each side of the brain had a mind of its own.
It is from these observations, with a handful of patients with atypical brains and disconnected hemispheres, that the theory of left-right brain dominance may have emerged and taken on a pop-psychology life of its own.
But in reality the two hemispheres are not disconnected. They are heavily interconnected, and information travels between them almost instantaneously — in less than 200th of a second.
It is not possible in a healthy, normally functioning brain for someone to selectively use one side or the other. Although processing is distributed across the brain, the brain works as a single entity, not as two independent competing halves.
Modern day imaging studies provide definitive evidence of brain function lateralisation. In a large-scale 2013 review of brain images from 1011 individuals, the scientist authors conclude that there are indeed hubs of activity that are largely lateralised to one side of the other. Language, and core regions of what is known as the Default Mode Network (activity that may relate to self-reflection or internal monitoring) tend to be left lateralised. On the other hand, the neural network involved in monitoring the external environment — attention and visuo-spatial processing, tend to be right lateralised.
Although some of the processes related to being creative may sit in the right hemisphere, there is no current evidence that how we think or use different cognitive strategies is lateralised. Research, in fact, points to just the opposite. People who performed well on a creative task showed greater activation on both sides of the brain, compared to people who performed less well on this task. And people with creative careers showed more whole brain activation compared to those in non-creative professions.
This speaks to a singular truth about the brain — it works as a whole. You are a whole brain thinker by nature.
And yet the myth persists.
It may be that this particular myth is so sticky because it is an easily understood and deployed metaphor — a convenient short cut for categorising different styles of thinking or cognitive competencies. But it is not based on facts about the brain. It is not based on neuroscientific evidence. No one is left or right brained, and everyone who has a healthy, normal brain uses both halves pretty equally.
Unfortunately, however, it is a metaphor that is easily manipulated by marketers of brain training to sell their programmes and books. Whilst it is an excellent idea to look at problems through different perspectives, to try your hand at different things and to learn new ways of thinking, in all cases, you are engaging your whole brain regardless of which approach you take.
by Sharlene Zeederberg
