Study topic · about 3 minutes
Left brain and right brain
The two hemispheres of the brain look alike, but they specialize: in most people the left hemisphere leads for language, and the right for attention to space and for parts of face and emotion processing. They share information through the corpus callosum. But the popular idea that people are either 'left-brained' or 'right-brained' is a myth: everyone uses both sides.
Key points
- Each hemisphere controls and feels the opposite side of the body, which is called contralateral organization.
- Language is mainly in the left hemisphere in about 95 percent of right-handed people, and in most left-handed people.
- The corpus callosum, a band of about 200 million axons, connects the two hemispheres.
- Split-brain patients, whose corpus callosum was cut to treat severe epilepsy, showed that each hemisphere can know things the other doesn't.
- A large brain-scan study found no sign that some people rely on one whole hemisphere more than the other.
Two halves, crossed over
A deep groove splits the cerebrum into left and right hemispheres. Most pathways cross the midline, so the left hemisphere moves and feels the right side of the body, and the right hemisphere the left. Vision crosses too: at the optic chiasm, the fibers from the inner half of each eye cross over, so everything you see to your left ends up in the right hemisphere.
What each side is best at
| Usually leads on the left | Usually leads on the right |
|---|---|
| Speaking and grammar (Broca's area) | Paying attention to both sides of space |
| Understanding language (Wernicke's area, in the superior temporal gyrus) | Recognizing faces |
| Reading and writing | The tone and emotion of a voice |
| Planning sequences of movements | Spatial skills, like turning objects in your mind |
Specialization is a matter of degree: both hemispheres take part in almost every task.
What split-brain patients showed
In the 1960s, some people with severe epilepsy had their corpus callosum cut to stop seizures from spreading across the brain. Roger Sperry and Michael Gazzaniga then tested them by flashing a picture to just one side of their vision, so that only one hemisphere saw it.
- When a word was shown in the right visual field, which goes to the left hemisphere, patients could say it.
- When it was shown in the left visual field, which goes to the right hemisphere, they said they saw nothing, yet their left hand could pick out the matching object.
The talking left hemisphere would even make up reasons for what the left hand did. These experiments showed that each hemisphere can perceive, remember and act on its own. Sperry shared the Nobel Prize in 1981 for this work.
Are people left-brained or right-brained?
No. The idea that logical people are 'left-brained' and creative people 'right-brained' grew out of split-brain research but goes far beyond it. In 2013, researchers at the University of Utah analyzed brain scans of more than 1,000 people and found that, although some networks lean to one side, people don't use one whole hemisphere more than the other.
When one side is damaged
The brain can rewire itself, especially in childhood. Children who have most of one hemisphere removed or disconnected to stop severe seizures can often still walk, talk and go to school, because the other side takes over many of its jobs. This ability to reorganize is called plasticity.
Quick quiz
5 questions. Your answers are saved and come back in your daily review.
Which structure connects the left and right hemispheres?
Show the answer
Corpus callosum. The corpus callosum carries about 200 million axons between the hemispheres.
Corpus callosum. The corpus callosum carries about 200 million axons between the hemispheres.
In most people, which hemisphere leads for language?
Show the answer
The left. Broca's and Wernicke's areas are usually in the left hemisphere.
The left. Broca's and Wernicke's areas are usually in the left hemisphere.
A split-brain patient sees a word only in the left visual field. What happens?
Show the answer
They can't name it, but the left hand can pick the matching object. The word reaches only the right hemisphere, which can guide the left hand but can't speak.
They can't name it, but the left hand can pick the matching object. The word reaches only the right hemisphere, which can guide the left hand but can't speak.
Where do the fibers from the inner half of each eye cross to the other side?
Show the answer
Optic chiasm. At the optic chiasm, so each hemisphere sees the opposite half of the world.
Optic chiasm. At the optic chiasm, so each hemisphere sees the opposite half of the world.
Is it true that people are either 'left-brained' or 'right-brained'?
Show the answer
No: everyone uses both hemispheres. Brain scans show no one relies on one whole hemisphere; both work together.
No: everyone uses both hemispheres. Brain scans show no one relies on one whole hemisphere; both work together.
These parts now come back in your daily review, just before you would forget them.
Practice these parts in 3DIn these study guides
- MCATLateralization and how the brain is studied
- AP Psychology1.4 The brain
- Intro psychologyThe brain and spinal cord (section 3.4)
- Medical schoolCortex, language and lateralization
- A-level PsychologyHemispheric lateralisation and split-brain research
Take it further in 3D
- LanguageHearing, understanding, speaking, reading. A short guided lesson in the 3D app.
- SeeingFrom the eye to the back of the brain. A short guided lesson in the 3D app.
Sources
- An Evaluation of the Left-Brain vs. Right-Brain Hypothesis with Resting State Functional Connectivity MRI (Nielsen and others, 2013), PLOS ONE
- Anatomy and Physiology 2e, 13.2 The Central Nervous System, OpenStax
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