Monday, September 12, 2022

Perinatal stroke 2

In early February 2016, after reading an article featuring a couple of scientists at the Massachusetts Institute of Technology who were studying how the brain reacts to music, a woman felt inclined to email them. “I have an interesting brain,” she told them.

EG, who has requested to go by her initials to protect her privacy, is missing her left temporal lobe, a part of the brain thought to be involved in language processing. EG, however, wasn’t quite the right fit for what the scientists were studying, so they referred her to Evelina Fedorenko, a cognitive neuroscientist, also at MIT, who studies language. It was the beginning of a fruitful relationship. The first paper based on EG’s brain was recently published in the journal Neuropsychologia, and Fedorenko’s team expects to publish several more.

For EG, who is in her fifties and grew up in Connecticut, missing a large chunk of her brain has had surprisingly little effect on her life. She has a graduate degree, has enjoyed an impressive career, and speaks Russian—a second language–so well that she has dreamed in it. She first learned her brain was atypical in the autumn of 1987, at George Washington University Hospital, when she had it scanned for an unrelated reason. The cause was likely a stroke that happened when she was a baby; today, there is only cerebro-spinal fluid in that brain area. For the first decade after she found out, EG didn't tell anyone other than her parents and her two closest friends. “It creeped me out,” she says. Since then, she has told more people, but it's still a very small circle this is aware of her unique brain anatomy.

Over the years, she says, doctors have repeatedly told EG that her brain doesn’t make sense. One doctor told her she should have seizures, or that she shouldn’t have a good vocabulary—and “he was annoyed that I did,” she says. (As part of the study at MIT, EG tested in the 98th percentile for vocabulary.) The experiences were frustrating; they “pissed me off,” as EG puts it. “They made so many pronouncements and conclusions without any investigation whatsoever,” she says.

Then EG met Fedorenko. “She didn't have any preconceived notions of what I should or shouldn't be able to do,” she recalls. And for Fedorenko, an opportunity to study a brain like EG’s is a scientist’s dream. EG was more than willing to help.

Fedorenko’s lab is working to shed some light on the development of the vast array of brain regions thought to play a role in language learning and comprehension. The exact role of each has yet to be demystified, and exactly how the system emerges is a particularly tricky element to study. “We know very little about how the system develops,” says Fedorenko, as doing so would require scanning the brains of children between the ages of 1 and 3 whose language abilities are still developing. “And we just don't have tools for probing kids’ brains at that time,” she says.

When EG turned up at her lab, Fedorenko recognized that this could be a golden opportunity for understanding how her remaining brain tissue has reorganized cognitive tasks. “This case is like a cool window to ask that kind of question,” she says. “It’s just sometimes you'd get these pearls that you try to take advantage of.” It's incredibly rare for someone like EG to offer themselves up to be poked and prodded by scientists.

For most people, the majority of language processing takes place in the brain’s left hemisphere. For some, the load is split equally between the two hemispheres. Even more rarely, the right hemisphere takes up most of the task. (Scientists are not quite sure why, but if you're left-handed, it seems you're “likely to wire up your language system in the right hemisphere,” says Greta Tuckute, a doctoral student in Fedorenko’s lab and the first author of the paper.)

Language processing largely takes place in two major parts of the brain: the frontal and the temporal regions. The temporal lobes develop first; then the frontal areas develop later, at around 5 years old. At this point, the language network is considered fully mature. Because EG’s left temporal lobe is missing, Fedorenko’s team had a chance to answer an interesting question: Are the temporal regions a prerequisite for setting up the frontal language areas?

In their first paper based on studying EG’s brain, they wanted to know whether she showed language activity in her fully intact left frontal lobe. If she did, that would suggest frontal language areas can emerge without the need for a preexisting temporal lobe in the same hemisphere. But if she didn’t, it would suggest that temporal language areas are a must-have for the emergence of the frontal ones.

The researchers used functional magnetic resonance imaging, or fMRI, to capture EG’s brain activity while she performed certain word-related tasks, such as reading sentences. As she did, they looked for evidence of language activity in her left frontal lobe. Then they compared this brain activity to around 90 neurotypical controls (similar data from people with intact left temporal lobes). Ultimately, they found none, so they concluded that the existence of temporal language areas appears to be non-negotiable for the emergence of the frontal language areas.

Still, they found that her left frontal cortex is perfectly capable of supporting high-level cognitive functions, which they confirmed by asking her to perform math tasks while watching how her brain responded. They concluded that in the absence of her left temporal lobe, the task of language processing seems to have simply shifted over to EG’s right hemisphere. A single hemisphere appears to be sufficient to give her proficient language skills.

Just how remarkably little effect the uniqueness of EG’s brain has on her day-to-day life shows how sheerly expendable big chunks of our brains can be. Fedorenko points to a surgical practice called hemispherectomy used for children with epilepsy whose condition does not respond to medication. The practice entails removing the half of the brain where the seizures are taking place, and these children have been shown to retain typical cognition. “If you can remove half of a brain and you work fine, that suggests there's a lot of bits in our typical brains that are redundant,” says Fedorenko. “There's apparently a lot of stuff in our brain that is fully redundant, which is—engineering-wise—a pretty good way to build the system.”

The reality is that if the brain is damaged, it will often find a way to rewire itself. This is something Ella Striem-Amit, a cognitive neuroscientist at Georgetown University, understands well. She studies how the brain reorganizes itself in the absence of certain senses, such as in people born blind or deaf. “The remarkable thing about this patient—and other such patients who were missing large chunks of their language system at birth, or other systems at birth—is how well they can compensate,” she says.

Specifically, if the abnormality develops in childhood, when neuroplasticity is stronger, another part of the brain will usually just make up for the function of the missing bit by forming new neural connections that take up the task. “There's been ample research over decades showing that the brain is way more flexible in early life,” says Striem-Amit. 

Drawing any conclusions from the observation of a single person might seem premature. In recent years, studies of individuals have gotten a bad rap because smaller studies can return fluke results. There’s been a widespread move in research toward bigger being better. But case studies, by and large, laid the foundation of modern neuroscience. Take famous examples like Broca’s patient, who in 1861 taught scientists which part of the brain controlled speech production; the patient H.M., whose brain unraveled the mystery of how memories organize themselves in the brain; and perhaps the most famous, Phineas Gage, a railroad worker who had an iron rod driven straight through his brain in 1848 and whose personality changes following the injury are thought to have shown for the first time that some functions are associated with specific regions of the brain. “All the core discoveries leading to our understanding of the brain started out with case studies,” says Striem-Amit. “We couldn't have figured out as much as we did and say something about causality without those unique cases.”

Fedorenko says that looking at high-quality data in an individual, as opposed to at a group-level map, is akin to “using a high-precision microscope versus looking with a naked myopic eye, when all you see is a blur.” Done carefully, an n=1 approach can offer trailblazing illuminations, such as in the case of EG, Fedorenko argues. “We can learn a huge amount of information from cases where something is a little bit different,” she says. “It just seems a shame not to take advantage of these accidents of nature.” 

“It's really important to study unique cases,” Striem-Amit agrees. “There's a trend toward big data, and we need to emphasize the importance of deep data—of studying very detailed experimental designs of individuals to understand how an individual brain is organized.”

Going forward, Fedorenko’s lab hopes to learn much more from EG’s brain. In a preprint posted online last month that has not yet been peer reviewed or published by a journal, they looked at a brain region called the visual word form area, which is thought to be responsible for decoding the written forms of words. In neurotypical people, the region is found in the left ventral temporal cortex; but for EG, the function is distributed throughout her brain, and she’s a “really good, fast reader,” says Fedorenko. For a future study, they’re also looking into how EG’s missing temporal lobe affects her auditory system. 

Remarkably, EG’s sister is missing her right temporal lobe and is largely unaffected by it, suggesting there's likely some genetic component to the early childhood strokes that can explain the missing brain regions, Fedorenko says. Next up, the team wants to use both EG and her sister—who has also volunteered to be studied—to try to understand how social and emotional processing takes place predominantly in the right hemisphere. In fact, the whole family is getting involved. A third sibling and EG’s father have also had their brains scanned, although it turns out they each have two intact temporal lobes—or a “boring brain,” as EG dubs it. A fourth sibling will be scanned in the near future. For a long time, it had never occurred to EG that anybody would want to study her, so she is just glad that the neuroscience field has been able to learn something from her brain. “And I hope that it will also take some stigma away from atypical brains,” she says.



1 comment:

  1. Tuckute G, Paunov A, Kean H, Small H, Mineroff Z, Blank I, Fedorenko E. Frontal language areas do not emerge in the absence of temporal language areas: A case study of an individual born without a left temporal lobe. Neuropsychologia. 2022 May 3;169:108184. doi: 10.1016/j.neuropsychologia.2022.108184. Epub 2022 Feb 17. PMID: 35183561.

    Language processing relies on a left-lateralized fronto-temporal brain network. How this network emerges ontogenetically remains debated. We asked whether frontal language areas emerge in the absence of temporal language areas through a 'deep-data' investigation of an individual (EG) born without her left temporal lobe. Using fMRI methods that have been validated to elicit reliable individual-level responses, we find that-as expected for early left-hemisphere damage-EG has a fully functional language network in her right hemisphere (comparable to the LH network in n = 145 controls) and intact linguistic abilities. However, we detect no response to language in EG's left frontal lobe (replicated across two sessions, 3 years apart). Another network-the multiple demand network-is robustly present in frontal lobes bilaterally, suggesting that EG's left frontal cortex can support non-linguistic cognition. The existence of temporal language areas therefore appears to be a prerequisite for the emergence of the frontal language areas.