aqa  A2 Only: Localisation of function in the brain and hemispheric lateralisation: motor, somatosensory, visual, auditory and language centres; Broca’s and Wernicke’s areas, split brain research. 


“The great pleasure and feeling in my right brain is more than my left brain can find the words to tell you.” – Roger Sperry

Certain brain functions tend to be more lateralised to either the right or left side of the brain, for example verbal functions tend to dominate the left side of the brain and visuospatial functions the right side. This is the same for all people and both hemispheres of the brain are still involved in these processes.

(For a brush on on areas of the brain, check this page).

Broca’s and Wernicke’s areas

One of the first researchers to discover the lateralisation of functions was Pierre Paul Broca in 1861, who had a patient nicknamed ‘Tan’ who was unable to produce speech. He discovered, during an autopsy, that tan had suffered a lesion in the left cerebral hemisphere (now called Broca’s area), whose role we now understand to be responsible for speech output. This ability was completely impaired by damage to just the frontal lobe of the left hemisphere. This area is now called ‘Broca’s Area’.

Wernicke’s area is associated with other aspects of language, and is named after the German physician Carl Wernicke. In 1864, Wernicke described a patient who was able to speak, but unable to comprehend language. The patient was found to have a lesion in the posterior region of the temporal lobe.

broca

Split-Brain Research

In the 19th century, research on people with certain brain injuries, made it possible to suspect that the “language center” in the brain was commonly situated in the left hemisphere. One had observed that people with lesions in two specific areas on the left hemisphere lost their ability to talk, for example.

What Does “Split Brain” Mean? 

The final evidence for this, however, came from the famous studies carried out in the 1960s by Roger Sperry and his colleagues. The results of these studies later led to Roger Sperry being awarded the Nobel Prize in Physiology or Medicine in 1981. Sperry received the prize for his discoveries concerning the functional specialisation of the cerebral hemispheres. With the help of so called “split brain” patients, he carried out experiments (just like the one you can perform by yourself in this Split Brain Experiments Game), and for the first time in history, knowledge about the left and right hemispheres was revealed.

In the 1960s, there was no other cure for people who suffered from a special kind of epilepsy than by cutting off the connection, corpus callosum, between the two hemispheres. Epilepsy is a kind of storm in the brain, which is caused by the excessive signaling of nerve cells, and in these patients, the brain storm was prevented from spreading to the other hemisphere when the corpus callosum was cut off. This made it possible for the patients to live a normal life after the operation, and it was only when carrying out these experiments one could notice their somewhat “odd behavior.”

Each hemisphere is still able to learn after the split brain operation but one hemisphere has no idea about what the other hemisphere has experienced or learned. Today, new methods and technology in split brain operation make it possible
to cut off only a tiny portion and not the whole of the corpus callosum of patients.

Some experiments into split-brain patients involved flashing words up a computer screen to either the left or the right eye only. Split-brain patients were only able to reporting ‘seeing’ the word when it was presented to their right eye (linked to the left hemisphere), but not their left eye (right hemisphere).

of-two-minds

What Came Out of the Split Brain Experiments?

The studies demonstrated that the left and right hemispheres are specialised in different tasks. The left side of the brain is normally specialised in taking care of the analytical and verbal tasks. The left side speaks much better than the right side, while the right half takes care of the spatial/perception tasks and music, for example. The right hemisphere is involved when you are making a map or giving directions on how to get to your home from the bus station. The right hemisphere can only produce rudimentary words and phrases, but contributes emotional context to language. Without the help from the right hemisphere, you would be able to read the word “pig” for instance, but you wouldn’t be able to imagine what it is.

Gender and Brain Lateralisation

Very recent research (2013) has given evidence for gender differences in verbal and spatial ability.

Brains

Credit: Image from The Independent.

It is known that if males suffer damage to the left hemisphere of the brain, then verbal ability can suffer as a result. Females, on the other hand, are better able to compensate for such damage. The key to this gender difference may lie in the fact that females have greater connectivity between the two hemispheres of the brain (and can thus better compensate for such damage), whilst males have greater connectivity within each hemisphere.


Brain2Go Further


Source: Boundless. “Cerebral Hemispheres and Lobes of the Brain.” Boundless Psychology.  https://www.boundless.com/psychology/textbooks/boundless-psychology-textbook/biological-foundations-of-psychology-3/structure-and-function-of-the-brain-35/cerebral-hemispheres-and-lobes-of-the-brain-153-12688/