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 |
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.
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.