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.
https://www.wired.com/story/she-was-missing-a-chunk-of-her-brain-it-didnt-matter/
