What happens if you remove half of the brain?

The human brain is the command center of the nervous system. It receives signals from the senses and transmits information to the muscles, and in certain areas of the left or right hemisphere, depending on the activity, forms new neural connections, in other words, it learns. But what if, as a result of treatment for a serious illness, a person was not simply disconnected from part of the brain, but physically removed one of the hemispheres?

Is it possible to live with only half of the brain, and what kind of life will it be?

Believe it or not, it will not be so easy to distinguish such a person from a healthy one. This wrinkled and mysterious organ that we carry in our turtles has an almost magical ability to change and adapt. It contains about 86 billion nerve cells - neurons - the very "gray matter", and the "white matter" consists of billions of dendrites and axons. All this is intertwined with trillions of connections or synapses, and each cell here has a special account.

In 2019, a team of researchers at the California Institute of Technology analyzed the brains of six adults between the ages of 20 and 30 who had undergone hemispherectomy, a rare neurosurgery to remove half of the brain. This procedure is indicated in extreme cases of epilepsy and has been carried out since the end of the 19th century. The authors also analyzed the brains of a control group of six healthy people who had both hemispheres. All participants underwent functional magnetic resonance imaging.

The results showed that in single-hemispheric patients, the brain networks, which are responsible for vision, speech, and many other functions, were remarkably intact and function in the same way as in healthy people. Moreover, the authors found that the connection between parts of different networks and their density is actually higher in those patients who underwent hemispherectomy. Therefore, the brain is able not only to adapt to conditions, but also to compensate for the loss of organ integrity without loss of functionality.

In 2014, a seven-year-old boy with severe epilepsy had his right occipital lobe, which contains the visual center, and most of his right temporal lobe, which contains the sound center, were removed. The fact is that our brain uses both hemispheres for image processing: the left is responsible for the right side of our visual field, the right for the left side. When we look straight ahead, our brains combine visual information into one picture.

The boy's brain, in the absence of the right side of the occipital lobe, adapted. Imagine taking a panoramic shot and moving the camera to capture the entire scene. This is how the boy's visual system began to work. Moreover, both of his eyes are completely healthy and receive information, but since there is no processing center on the right side of his brain, this information simply has nowhere to go. This is another example of plasticity: brain cells begin to form new neural connections and take on new tasks.

The brain scan of a 29-year-old woman was puzzling to say the least. It turned out that she lacked certain brain structures that are necessary for smelling, but her sense of smell was even better than that of the average person. Scientists cannot yet fully decipher this phenomenon, but it is absolutely clear that the brain is able to replace idle or absent centers. It is for this reason that another part of the girl's brain took on the task of processing odors.

Of course, things are not so simple, the speed and ability of the brain to adapt depends on many factors, including age, so scientists at the California Institute of Technology are working on a new study. They hope to better understand exactly how the brain reorganizes itself after injury, surgery, or stroke, and how certain areas of the brain are able to compensate for those that are damaged or lost. But the fact remains - without half of the brain, a person is able to live and lead the same lifestyle as one who has brains in place.