Many doctors were puzzled to see the results of her brain imaging. Because, according to their understanding, such a brain defect should bring about serious functional deficits. Finally, she couldn't stand the doctors who commented on her brain and contacted a team of scientists in the hope of solving the mystery of her brain with the help of scientists. And the scientists were rewarded with a treasure ......

It wasn't until she was 25 that she knew her brain was a little different from the average person.

Had it not been for that brain scan that made her understand that she was missing a piece of her brain, she might never have discovered the secret. Because growing up, her daily life seemed to be unaffected, and she went to college and graduate school as she should.

The brain region she is missing is the left temporal lobe. For most people, this is a critical area that carries language functions, and the corresponding location in her brain has nothing more than cerebrospinal fluid. One doctor once thought that her vocabulary would be no better than that of a fifth grader, but in fact she scored in the top 2% of the population on the verbal IQ test. Not only that, but she is a native English speaker who is also fluent in Russian, a foreign language.

Over the years, many of the doctors she saw could not believe that such a unique brain could perform so well. At the same time, she became more and more curious about her own brain. Finally, in 2016, she contacted a team of scientists at the Massachusetts Institute of Technology (MIT) and became the subject of their prized research.

Recently, the first paper on her (brain) was published, in which she goes by the pseudonym EG. From her mind, scientists have discovered some secrets of the language development process.

The left brain is not enough, the right brain will come

The human brain is divided into two hemispheres, the left and right, and each hemisphere has four lobes: the frontal lobe in front, the temporal lobe on the outside, the parietal lobe above, and the occipital lobe at the back.

Among them, language functions are mainly performed by the temporal and frontal lobes. The temporal lobe carries an important area called Wernicke's Area, located at the junction of the temporal and parietal lobes, which helps us understand language, whether it is the speech we hear or the words we see; the frontal lobe also has an important area called Broca's Area, which selects the right words for us to express our thoughts.

Both the left and right brain have temporal and frontal lobes, but the functions of the two brain hemispheres are different. For most people (85-90%), the left brain will become the primary bearer of language processing and the dominant hemisphere, while the function of the right brain language area will be suppressed.

If you recall, it was the temporal lobe of the left side of the brain that EG, the main character of this article, lost. However, her language skills were not significantly deficient and were even better than normal (except for spelling errors). Therefore, scientists cherish this case that came to them.

In EG's memory, she never suffered any head trauma, or the defect in her brain was most likely congenital. A common cause of such phenomena is perinatal stroke: a stroke that occurs in a fetus or infant between the 140th day of pregnancy and the 28th day after delivery. The research team believes that EG's left temporal lobe deficit may also be due to this disorder.

And in the face of early injury, the human brain possesses a degree of resilience. In previous studies, some scientists have observed that after a perinatal stroke occurs, some children do not lose their speech, as we generally think of stroke victims, but develop speech abilities similar to those of normal people.

This is because neuroplasticity is stronger in infancy and early childhood. If one brain region is damaged, other brain regions can establish new neural connections to perform the corresponding tasks and compensate for the missing functions. There have been cases where the right side of the brain can take over language functions after early damage to the left side of the brain. This suggests that in the young brain, both the left and right brain can actively perform language processing tasks. Or, at that time, the left brain has not really dominated and become the dominant hemisphere, and the right brain has the opportunity to take over.

Since, as scientists once knew, the human brain is set up for "redundancy", one area is damaged and there is still a chance for other areas to fill in. So, what else can the research team from MIT find out from the EG brain?

What about the frontal lobe without the temporal lobe?

In the adult brain, there is a frontotemporal network needed to process language. However, to say how this language network arises was not previously well understood by scientists.

Before encountering this particular case of EG, scientists often struggled to obtain data on the brains of 1 to 3 year olds, which is the main period of language development; there is already a lot of data on 4 to 5 year olds and even early adolescence, but those brains have developed to near adult levels, and if there is a significant difference, it is that the functional specialization of the left and right brains is not yet complete, but this hardly provides researchers with inspiration about the developmental process.

The frontal language areas, for example, usually develop to a level similar to that of adults around the age of 5; and the temporal language areas develop earlier than the frontal language areas. Scientists have always wondered if the presence of the temporal language area is a prerequisite for the production of the frontal language area.

With EG's brain in hand, the research team was able to design experiments to find out. They gave EG some reading tasks while relying on fMRI (functional magnetic resonance imaging) to monitor her brain activity and compare it to that of 94 adults whose brains were developing without abnormalities. These 94 controls were also native English speakers, as was EG.

Specifically, the task is to read real sentences and fake sentences. In a real sentence, each word is an actual English word and is arranged in a meaningful combination; in a fake sentence, each "word" can be read according to its spelling, but it is not an actual English word and does not express any meaning.

The length of each sentence is 12 words, regardless of whether it is a true sentence or a false sentence. Instead of appearing directly on the screen, each sentence was popped up word for word, with 450 milliseconds between words. all EG and other controls had to do was read the sentences silently. The researchers said the task targeted brain areas associated with lexical-semantic processing and combinatorial processing.

During the experiment, the scientists mainly looked at the left frontal lobe of EG to see if there was any language-related neural activity in this area. If there is, it means that in the absence of the left temporal lobe, the left frontal lobe can still develop language function. That is, the same hemisphere does not need the presence of a temporal lobe to produce a frontal language area. If not, it could mean that the left frontal lobe did not develop language function in the absence of the left temporal lobe. Alternatively, the temporal lobe must be present in the same hemisphere in order to produce a frontal language area.

As a result, the team did not find language activity in the left frontal lobe of the EG, while both the frontal language area and the temporal language area of the right brain were working. The scientists thus hypothesized that the presence of temporal lobes in the same hemisphere is necessary to produce frontal language areas. In the absence of the left temporal lobe in EG, even if the frontal lobes of the left and right brain are interconnected, the left frontal lobe cannot use this to acquire language function.

So, could it be that the left frontal lobe of EG is unresponsive to any higher cognitive tasks? The team tested EG again with some additive arithmetic problems, and the results showed that EG's left frontal lobe still retained other higher cognitive functions, but just lacked language functions. Thus, the scientists became more and more convinced that the frontal language area cannot exist independently of the temporal language area (in the same brain hemisphere).

EG's frontotemporal language network is provided entirely by the right hemisphere of her brain. This also indicates that one hemisphere is sufficient to guarantee her intact language function.

Start with a special case

Of course, one person's case is not representative of others. just because EG had an organic brain injury that did not cause her developmental delay does not mean that other children with similar brain injuries will not also have developmental delays. This case study is just the beginning.

However, many important discoveries in the field of neurology have also started with a single case. For example, as mentioned above, there is an important area in the frontal lobe called Broca's area, which is responsible for producing language. This area was named after a doctor named Pierre Paul Broca. In the 1860s, Dr. Broca found a lesion in the left frontal lobe of a patient who could only produce the sound "tan" after he passed away, and later found similar damage in more than 20 other patients with similar symptoms. Thus, he proved that the brain does have regional specialization and that different brain regions are responsible for different functions.

Another decade or so later, a neuroscientist named Carl Wernicke followed in Broca's footsteps and found another area of damage in the brains of patients who could speak fluently but couldn't understand what they were saying. That is Wernicke's area, located in the temporal lobe (which also extends to the parietal lobe), which helps to receive and understand language.

Today, MIT scientists are continuing their research on the EG brain. Since the temporal lobe is not only responsible for language functions, it is also involved in some auditory perception. Next, the team intends to continue to see how the absence of the left temporal lobe affects EG's auditory system.

In addition to this, EG herself mentioned that in addition to the missing piece of her brain, a part of her brain stem was also missing. A number of years ago, a doctor once told her that similar phenomena had been seen only in the brains of dead babies and that any damage to the brainstem was thought to be fatal. However, with the development of brain imaging technology, cases similar to hers are becoming more common.

Today, EG is over half a century old, but she still hopes that she can help people understand more about the possibilities of the brain as a special case.

"My brain is unique, not abnormal!"

Original paper.

https://www.sciencedirect.com/science/article/abs/pii/S0028393222000434?via%3Dihub

Reference link.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6291004/

https://www.pnas.org/doi/10.1073/pnas.1905590117

https://www.wired.co.uk/article/she-was-missing-a-chunk-of-her-brain-it-didnt-matter