Tech UPTechnologyCan you live with only half a brain?

Can you live with only half a brain?

 

Our brain is capable of amazing things. Reading this article, for example, is part of that set of daily tasks that, without realizing it, require putting into action a considerable number of brain structures and cognitive processes , from recognizing visual stimuli to remembering the meaning of symbols , decode them and reason their meaning. A great little feat of evolution .

Even with severe damage , the brain can still do its job quite effectively. Even when these damages involve missing a part of the brain , sometimes half .

So the answer to the question , can you live with half a brain , is a resounding yes . It is not common, being usually the result of surgery .

It is clear that the idea of giving up a part of our brain is not exactly pleasant for us. Unfortunately, there are some neurological conditions, as well as certain malformations , that put us in a very difficult situation.

Among these pathologies are severe epilepsies that do not respond well to pharmacological treatment . Seizures are sometimes caused by diseases such as Rasmussen’s encephalitis or a congenital vascular disorder called Sturge-Weber syndrome .

In a few cases, when other therapeutic measures are not effective, a measure that is initially frightening is recommended: disconnect or remove half of the brain , to stop the seizures related to the disease .

 

Although it is now in disuse , until decades ago the intervention used to involve removing the entire damaged hemisphere . When that happens, it is called an anatomical hemispherectomy .

The first documented hemispherectomy of this type was performed by the German physiologist Friedrich Goltz in 1888 . Of course his patient was not a person, but a dog .

It was the American neurosurgeon Walter Edward Dandy who, in 1923 , performed an anatomical hemispherectomy on a person affected by a malignant brain tumor at Johns Hopkins University .

Back then, gliomas , tumors that developed in the brain and spinal cord, were considered incurable . The surgeon noted that certain tumors caused contralateral hemiplegia , that is, loss of motor function on the side of the body opposite the damaged hemisphere.

Dandy assumed that the hemispherical tissue was of no use, and decided to remove it entirely. Of the five patients he operated on, two of them died three months later, due to a recurrence of cancer, but there was another who lived more than three years . A milestone for the time, although nowadays the treatments have changed.

Returning to the severe cases of epilepsy that we mentioned above, functional hemispherectomy is currently the preferred technique. It consists of cutting sections of the affected hemisphere (and the corpus callosum , which joins both hemispheres), to prevent epileptic seizures from spreading. It would be something like neurally disconnecting the diseased hemisphere .

Today, functional hemispherectomies are an intervention that is performed with great success , achieving good control of seizures in cases of severe epilepsy and improving the clinical symptoms of patients with extensive hemispheric lesions .

Naturally, such an operation has its drawbacks , such as loss of control of the hand opposite the disconnected or removed hemisphere, as well as loss of half the visual field in each eye.

But the most striking thing is that disconnecting half the brain, even if it is the left hemisphere (the one most related to the control of language , syntax and semantics ), does not prevent patients from speaking, studying and leading their lives normally .

How is it possible?

 

Brain plasticity, the great secret

That the brain is plastic means that it is capable of adapting , molding itself and being dynamically affected by the environment. This allows us to develop and reorganize the brain as we have experiences throughout our life cycle . The processes of memory consolidation, learning and recovery after brain damage depend on plasticity .

Thanks to the great plasticity of the brain, the functional hemisphere can be reorganized to compensate for the absence of half the brain after hemispherectomy . Such capacity continues to surprise experts , who until relatively recently continued to have the static conception that the brain would mature until adolescence , to remain stable at later ages.

It used to be thought that if the hemisphere was removed after the age of two, the operated child would never speak again. Fortunately, it is not. It does happen that the plasticity of infant brains is much more powerful than that of adult brains, which is why hemispheric disconnections are preferably carried out at a very early age.

The same brain plasticity that allows children to learn everything so quickly is what reduces the chances of language problems when they live with only their right hemisphere functional.

If the striking MRI images with half brains correspond to healthy adults and with normal lives, it is because the important functions that our brain carries out are not assigned to unique and distinct brain regions , but are supported by multiple regions . If one structure is damaged, the others can compensate , taking over.

Evolutionarily speaking, it might make sense that an organ as important as the brain is prepared to withstand changes and adaptations of such magnitude. Well, as far as biology is concerned, living with half a brain is better than not living at all.

 

References:

Kim, J. S. et al. 2018. Hemispherotomy and functional hemispherectomy: indications and outcomes. Journal of epilepsy research, 8(1), 1. DOI: 10.14581/jer.18001

Kliemann, D. et al. 2019. Intrinsic functional connectivity of the brain in adults with a single cerebral hemisphere. Cell reports, 29(8), 2398-2407. DOI: 10.1016/j.celrep.2019.10.067

Maier, M. et al. 2019. Principles of neurorehabilitation after stroke based on motor learning and brain plasticity mechanisms. Frontiers in systems neuroscience, 13, 74. DOI: 10.3389/fnsys.2019.00074

McGovern, R. A. et al. 2019. Hemispherectomy in adults and adolescents: Seizure and functional outcomes in 47 patients. Epilepsia, 60(12), 2416-2427. DOI: 10.1111/epi.16378

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