You must be “left-brained.” Creative, artistic and intuitive? You must be “right-brained”. Personality quizzes and career advice passed down through generations have many of us thinking we’re powered by one side of our brain that dominates our thinking style and explains our personality.
But is this the truth or fiction? And how did this idea come about? To find out, we need to go back more than 150 years.
The science behind this idea goes all the way back to the 1860s. That’s when French doctor Paul Broca found speech was controlled mainly by the left side of the brain. This was the first evidence the brain’s two halves may have separate roles.
A century later, Nobel laureate Roger Sperry extended this idea. He and his team studied people who’d had brain surgery to control their epilepsy. The surgery involved cutting the nerve fibres connecting the left and right sides of the brain, allowing them to examine each side individually.
For the first time, they could see what each hemisphere controlled. They found the left side was more specialised for controlling language and the right for emotional and non-verbal processing. The separation of tasks into one side or the other, or lateralised behaviour, is not a uniquely human trait.
Insects, fish, birds and other mammals do it too, not just primates. Genes that govern this are expressed early in human development, before the brain is fully formed. From an evolutionary perspective, scientists think having different halves of the brain specialising in certain tasks helped us do two things at once.
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