Are the Brains of Left Handed People Different to Right Handed People?

When I began my research into handedness, I assumed the brain of the left handed person was merely a mirror image of the right handed person. In fact, Phrenologists of yore believed both hemispheres were a mirror image of each other. We all have a mirror image of organs such as kidneys and lungs. The brain has two hemispheres, can’t the same apply?

Mistakes of Phrenology

Broca's Area and Wernicke's Area
in the Left Brain

In fact, scientists who studied the convolutions of the brain found it to be asymmetrical. The speech centre was discovered to reside in the left hemisphere only. This is known as Broca’s Area. The same area of brain on the other side has nothing to do with speech. So the function of the brain is asymmetrical too.

But in the case of left handed people, the speech centre is still located in the left side of the brain (the same as in right handed people). But it goes further than this. But let’s start at the beginning.

History of Brain Function Discovery

In 1836, Max Dax discovered that patients with damage to the left side of the brain had trouble understanding speech. This is where the notion of the linguistic ‘left brain’ began.

Little changed until 1861 when Paul Broca identified the precise location of Broca’s area, the speech centre (named after him). He noted that damage to this area disrupted speech but not comprehension. It wasn’t until 1874 that the brain cells that process comprehension was identified, called Wernicke’s areas, after Carl Wernicke. This was also in the left brain. As well as these skills, the left brain could do arithmetic and control fine motor skills.

And so for a long time, the left brain was lauded as the master of the two brains. Little was known about the mysterious right brain until the later discovery that special, music and visual abilities reside there.

Roger Sperry Split Brain Study

But in the mid 1060’s, a neuropsychologist called Roger Sperry broke new ground with his radical treatment for severe epilepsy. When all else failed, he resolved to sever the connective tissue between both hemispheres of the brain (called the corpus callosum). The operation alleviated the epilepsy but with the tissues severed, the two hemispheres could no longer communicate with one another. The effect on his patients was to say the least strange.

Left Hemisphere and the Right Hemisphere of the Brain

Sperry discovered that his patients could not vocalize the name of an object if an image of it was flashed to the right eye only (controlled by the left brain, where the speech centre is located). The only way to communicate the object, was to pick out a similar object from a box or to draw it (but only the left hand could do this, regardless of the patient’s dominant hand). The subject could vocalize the object if the image was flashed to the right eye. Sperry’s split brain research won him a Nobel prize in 1981.

Speech Recovery after Aphasia to Left Handed People

This goes back to my earlier assumption, that the brains of left handed people were merely a mirror image arrangement of right handed people. In fact Klaus Conrad, a doctor who treated hundreds of men with head wounds in World War 2 discovered that regardless of the handedness of the patient men who sustained wounds to the left side of the head suffered aphasia (impaired speech) regardless of handedness. So the brains of left handed people are not a mirror image of right handed people. 

The difference? Well, the brain function of the left handed person is less lateralized. Some left handers even have a small echo of linguistic ability in the right side of the brain (so the left hander has a better chance of speech recovery if suffering a stroke to the Broca’s Area). A small part of some Left handers’ left-brain also light up when recognizing faces – thought to be exclusively a right-brained function.

Brains of Left Handed People

So the brain of the left handed person is (on the whole) less lateralized in function. What does this mean for the left hander? MRI scans since the turn of the twenty-first century has proved this beyond a doubt. Some left handers when asked to perform a verbal task will cause Broca’s area to light up as well as a little echo on the right side. So a little of a left-brained function will be found in the right brain.

Lateralization of the brain is not so set in stone as it once was. In fact, the brain is flexible and always changing. However, on the whole, the specific functions of the brain can be found in particular sites. The right brain, however, still has mysteries yet to be solved.