Can you survive with half a brain?

In the next article we are going to talk about what keeps us alive, the cases of people without brains or without parts of the brain. We want to give a satisfactory answer to the question “Can you survive with half a brain?”

Can you survive with half a brain?

No, you can’t survive with half a brain. In most cases it is incompatible with life. A congenital malformation called anencephaly causes babies to be born without a brain, but either die at birth or are stillborn. The cases that the baby survives are very rare, but there are.

Can or can we not live without a brain ?: The minimum brain necessary for “life”

Continuing with what the subtitle above states, the minimum brain necessary for life is none. We quickly realize this when we look at the thousands upon thousands of species of animals, plants, and other kingdoms that do not require a brain to be alive. 

However, that answer is too simple. What interests us here is to know what is the minimum brain for life in species that do have one.

It seems easy to most of us to differentiate between someone living and someone dead. If we were faced with the difficult task of determining if someone is in one state or another, our first impulse would probably be to see if they move, feel if their heart beats, notice if they breathe, note their temperature or check their rigidity. 

All these “signs of life” depend in large part on the survival of a couple of parts of our brain: the brainstem and the hypothalamus.

What role do the brainstem and hypothalamus play in keeping us alive?

The brainstem is located at the bottom of what is commonly known as the brain. It is about the structure that connects our cerebral hemispheres with the spinal cord. 

It is classically divided into three parts: midbrain, bridge and medulla oblongata; and in them we find neural nuclei whose activity orchestrates a good part of the vital functions based on the brain, such as the movement of the viscera or the regulation of blood pressure.

There is also a center of essential importance for consciousness: the ascending activating reticular system.

The brain stem thus functions as a kind of life support device. It can be said that the brain from the brainstem up “is not indispensable” to maintain the living body. 

Of course, the ability to procure food, water and other necessary resources for our body is totally compromised if we have only a functional brain stem and not a fully functional brain, but as long as that structure remains healthy, strictly vital functions are kept and their owner is generally considered alive, in a vegetative state

Along with the brainstem, another brain structure is presented as important in maintaining this state of “life support”: the hypothalamus. In it are essential neurons to maintain vital autonomic functions such as thermoregulation.

Although technically it is possible to “survive” only with the brainstem, the work is very complicated when this other small structure is compromised by being able to incur high fever, excessive sweating or metabolic failures that complicate the prognosis much more.

It can be said that this small and primitive region is the seat of life. A systematic failure of the reflexes mediated by the brainstem indicates that there is irreparable damage to this structure, and this is one of the criteria for establishing brain death. In fact, the term “brain death” is commonly used to refer specifically to the death of the brain stem.

Damage to the brain stem is associated, in addition to death, with states called “disorders of consciousness”, such as coma, vegetative state or minimally conscious state.The typical cases in which we can verify the “life support” function of these structures are those that derive from common causes of a vegetative state, such as brain injuries or cerebral infarcts.


Vegetative state

Individuals in this state are considered to be unaware of themselves or their environment but have signs of activity, such as wake-sleep cycles, and behaviors and reflexes such as opening their eyes, smiling, crying, screaming, biting, startling and others mediated by the activity of the motor nuclei found in this portion of the brain.

So to speak, they are awake but are unable to perceive anything in their surroundings or themselves, and therefore not respond to any of it (although neuroimaging studies seem to be challenging this idea). 

In this state, patients are able to maintain their vital functions by themselves (breathing, regulating the heartbeat, intestinal functions, etc.), but they always need to be fed, washed and cared for. They cannot interact with their environment and much less speak, direct their eyes or make any other movement voluntarily.

However, there are two other approaches that reveal this distinguished work of the “minimum brain for life”: studies of animal decerebration and certain cases of anencephaly.

What is done in decerebration studies?

In decerebration studies, the front of the brain is removed. In this state, animals are capable of surviving several hours, being able to study in them some functions such as spinal motor reflexes, spinal and brainstem sensory-motor integration, cardiac and respiratory function, etc.

What are cases of anencephaly in humans?

Anencephaly is a malformation of the brain derived from a failure in uterine development that leads to the total or partial lack of this organ.

Those born with anencephaly often lack a functional brain beyond the brainstem. In addition, they often have other craniofacial abnormalities and problems in other organs and systems, such as the heart or urinary system.

Although the majority of children born with this malformation die on the day of birth or within a few days, there are some cases that challenge this dire prognosis.

The press reports on cases of anencephalic children who have been able to survive with a brain consisting mainly of only the trunk for months and even years. These children are considered to be non-conscious (despite some parents seeing genuine signs of conscious thought and will in their responses) but rather to be in a vegetative state.

Can you live normally with a “little” brain?

Some of the most striking (and controversial) cases of compatibility of life with “little” brains are carried out by people with hydrocephalus. In hydrocephalus, there is an abnormal accumulation of cerebrospinal fluid within the skull, and it may be present at birth or begin in adulthood.

It is a serious condition, as this accumulation puts the surrounding brain tissue at risk. However, the loss of brain tissue does not seem to be a problem for some people.

Case 1

In the article published in Science that launches in its headline a question similar to this one, Is Your Brain Really Necessary ?, its author exposes some cases that make this, a priori, silly question necessary.

It includes, for example, the case of a mathematics student with an IQ of 126 (the average is 100 and giftedness is 130), brilliant grades and a completely normal social life who turned out to have his skull practically invaded by cerebrospinal fluid.

In the words of the doctor who “discovered” his condition, John Lorber: “What we saw instead of normal tissue about 4.5 centimeters thick between the ventricles and the cortical surface was a thin layer measuring about 1mm” .

Along with this student’s case, the article indicates figures derived from this doctor’s treatment of other patients with hydrocephalus. According to his data, in 50% of individuals in whom the cerebrospinal fluid occupies 95% of their skull, they find an IQ greater than 100.

Similarly, in the same sample, he also found patients with severe disabilities. The article indicates that these cases of excessive thickening of the cerebral ventricles compatible with a normal life seem to be cases in which the thickening occurs slowly.

Case 2

Another similar case was reported in 2007 in The Lancet. This time the patient had an IQ of 74 (the cutoff for mental retardation is a score of 70), was married, and the father of two children.

Some researchers emphasize the extraordinary plasticity of brain tissue and its functional redundancy, especially during childhood, to explain these cases. 

Others prefer to be skeptical because the studies of these have been carried out only by means of magnetic resonance, a technique whose resolution, especially in the time of John Lorber, can be limited when it comes to exploring which tissue is intact and which is not.

Can you live without parts of the brain?

This question becomes much easier for us to answer since it is in the public domain that operations are performed daily to remove parts of the brain. Such is the case with lobotomies. 

Although in the past these operations were performed for therapeutic purposes that today make us look at this word almost as a synonym of atrocity, today they are still necessary in, for example, cases of intractable epilepsy.

Normally, the removal of parts of the brain entails some change in the functioning of the person, such as loss in the ability to memorize or changes in the ability to handle emotions, but the operation is perfectly compatible with life and is in fact performed to improve its quality.

Because the surgical removal or accidental loss of some part of the brain usually leads to changes or losses in brain functions, the cases of people who have been able to lead a normal life without realizing that they were missing are very striking. parts of your brain that are fundamental in principle in the eyes of medical science and neuroscience.

Again, it is the failures in brain development during the fetal stage that throw us cases capable of astonishing the most trained neuroscientist.

Cerebellar agenesis is one of those failures, which affects the development of the cerebellum. The cerebellum is a structure located in the ventral (lower) part of the brain, attached to the brain stem. 

It is a structure with a huge number of neurons (many more than in our entire neocortex) whose functions are classically linked, among others, to the coordination of movement.

In cerebellar agenesis, the development of this portion of the brain is interrupted, generating individuals that lack it. A cerebellar lesion usually leads to serious problems in the execution of movements, so logic tells us that an individual who completely lacks the cerebellum should be practically invalid.

Case 1

However, cases such as that of this Chinese woman who did not “realize” until she was 24 that she did not have a cerebellum, put that logic into question. To defend “the honor” of the cerebellum, it must be said that this patient had problems learning to walk, that she did not manage to do it independently until she was seven years old, and that she was always afflicted with dizziness and difficulty maintaining her gait. Even so, due to its degree of affection, it could not be guessed that it lacks the entire cerebellum.

In the attached scan image you can see the black hole in which this “little auxiliary brain” should be. In the same article the conditions shown by other patients with the same problem are attached. You can see most pay a “functional price” for that lack of cerebellum.

Another striking failure of brain development in the fetal stage occurs when one of the two cerebral hemispheres is not formed, that is, when half a brain is missing.

Case 2

Such is the case of patient AH, a girl who at the time of the study was 10 years old, a modest muscle weakness in the movements of the distal extremities on the left side, microphthalmia (literally, small eye) of the right eye and the absence of the right hemisphere.

Since many of the brain functions are totally or partially “distributed” between the two hemispheres, the little involvement of the girl is curious. 

The researchers who reported their case focused their study on how AH could have practically normal vision if each side of the visual scene is processed, in a “normal” brain, by the contralateral hemisphere.

If in a “normal” brain the left side of the visual field is processed by the right hemisphere and the right side by the left, in AH the entire visual field is processed by the occipital cortex of the only hemisphere it has.

What the researchers discovered is that the connections coming from the left side of both of this girl’s retinas had been reorganized and led to where they were going to “listen”, that is, the left hemisphere.

Why this girl can lead a normal life despite having only half of her brain can be understood because AH has never been able to “enjoy” more of that organ.

Scientists, again, allude to the extraordinary plastic capacity of this organ and to the functional redundancy to explain it. As it were, when developing under these conditions, the brain “does what it can with what it has” and adapts.

In this case, make up a whole brain in half space. For this reason, the effects are very different from those that usually appear when an already developed person has to have half of their brain removed (an operation called hemispherectomy).

In these cases, the consequences are much greater because that organism grew up with the entire brain mass and therefore was able to “distribute at will” the different functions in their corresponding places.

FAQS: Can you survive with half a brain?

What happens if you only have half a brain?

For example, when half of the brain is damaged, disconnected, or removed, it causes weakness on the opposite side of the body. In particular, the foot and hand on one side will be weaker. It also causes vision loss on one side of the visual field.

Can you still function with half a brain?

And yes, it can happen. It’s rare but there are few dozens of people who live without large parts of their brain, half or even less. These people weren’t born that way. Most commonly they had a disease in childhood, such as Rasmussen’s encephalitis, where epileptic seizures are very common.

What happened when a girl had half of her brain removed?

It was hard to tell she was suffering from a rare brain disease that caused seizures, twitches and loss of movement called Rasmussen’s encephalitis. Ben Carson performed a hemispherectomy, removing half of her diseased brain. The surgery was a success.

Can You be born with half a brain?

Anencephaly is a serious birth defect in which a baby is born without parts of the brain and skull. It is a type of neural tube defect (NTD). As the neural tube forms and closes, it helps form the baby’s brain and skull (upper part of the neural tube), spinal cord, and back bones (lower part of the neural tube).

What happens if you lose the right side of your brain?

About Right Hemisphere Brain Damage

The right side controls attention, memory, reasoning, and problem solving. RHD may lead to problems with these important thinking skills. A person with RHD may have trouble communicating with others because of this damage.

In the previous article we talked about what keeps us alive, the cases of people without brains or without parts of the brain. We wanted to give a satisfactory answer to the question “Can you survive with half a brain?”


Lewin, R (1980). Is your brain really necessary? Science 210(4475), 1232- 1234

Muckli, L., Naumer, M. J., & Singer, W. (2009). Bilateral visual field maps in a patient whith one hemisphere. Proceedings of the National Academy of Sciences, 106(31), 13034-13039.

Hydrocephalus Clinical Trials – Mayo Clinic Research. (2019). Retrieved December 13, 2020, from webside: