A lot of different popular science literature discusses the differences between the left brain and the right brain in terms of their differing functions. Though this is largely true, in actuality the differences between the functions of both hemispheres are quite varied with often a lot of overlap. In younger children, there is a great deal of neuronal plasticity (neuroscience lingo for ‘can change a lot’) which allows for brain regions to take on the functions of other, often surrounding, regions. In particular, if there is damage to one hemisphere of the brain, the equivalent brain region in the other hemisphere might take over this role.

What does each hemisphere do?

Each hemisphere begins looking roughly like a mirror image of the other hemisphere at the start of development. Throughout the growth of the foetus, each brain region becomes more specialised and takes on unique functions. The left hemisphere is predominantly in control of language production and comprehension, whereas the right only understands the prosody (melody) of speech. This isn’t the only brain function that is lateralised. A lot of mathematical and creative skills are dominated by one hemisphere, but, under the same principle, this may be altered in development.
One anatomical aspect of the brain that allows for particular functions to be lateralised to the left or the right hemisphere is that there are cells that run in tracts between the hemispheres of the brain which allow for the exchange of information. The largest of these communication channels is called the Corpus Callosum and it connects the left and right hemispheres.

When we talk about the brain we rarely talk about it as an electrical unit but that is essentially what it is. Neurons (brain cells) communicate with one another through electrical and chemical potentials and an electrical potential is what electricity. It’s basically the oldest computer-type thing that can perform multiple functions at the same time.

Whats the Corpus Callosum got to do with this?

The Corpus Callosum plays an important role in facilitating the communication of information between hemispheres. Science history, particularly old psychological practices can seem insane when we look back on it. Early practices of dealing with epilepsy (uncontrolled brain activity) were to cut the corpus callosum so that the uncontrolled electrical activity didn’t spread across the brain. The patients who had their corpus callosum cut were then used to study the role of the corpus callosum (split-brain patients).

One important discovery was that visual information is shared between the brain hemispheres to produce the full picture that we see. The cutting of the corpus callosum means each eye’s visual information is different after it is processed. In normal people, when you show the right brain a picture or a word both hemispheres of the brain can see it and we can say the word. We previously discussed at only the left hemisphere is the speaking part of the brain (sound production). In split-brain patients, the right brain can’t talk without the left brain so if we show the right brain something and ask the person what they see they will say they saw nothing. This is because their left brain cannot see anything; effectively they are two.

The split brain phenomenon is incredibly interesting. You can learn more in CGP Grey’s video: https://www.youtube.com/watch?v=wfYbgdo8e-8