While the human brain appears essential to being human, people can live normally — and even excel — with large parts of the brain missing or with brains that have been cut in half. That happened to EG, who grew up missing her left temporal lobe. As told at Wired:

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 that 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.

Grace Browne, “She Was Missing a Chunk of Her Brain. It Didn’t Matter” at Wired UK (April 12, 2022) The paper requires a fee or subscription.

EG has since become the subject of a paper published this month in Neuropsychologia by MIT cognitive neuroscientist Evelina Fedorenko and her team.

Study of EG has proceeded on the assumption that other regions of her brain had taken up the task of processing language. That’s not as unusual as it sounds; the brain is a living organ, not a machine. Given an opportunity, it can shift burdens around (neuroplasticity.) This is especially true if, as in EG’s case, the damage occurred when she was a baby. Children’s brains appear more neuroplastic than those of adults, probably because many thinking tasks have not yet been assigned.

Among people with intact brains the left hemisphere usually processes language. But left-handed people are more likely than others to have the right hemisphere doing that job. In EG’s case, the researchers concluded, based on functional magnetic resonance imaging (fMRI), that language processing had shifted to her right hemisphere. Her left frontal cortex could still do math tasks, however.

E.G. herself contributed to the paper in Neuropsychologia, writing a note as a participant of interest (possibly to establish that she was indeed fluent, articulate, and literate). It reads in part,

Please do not call my brain abnormal, that creeps me out. My brain is atypical. If not for accidently finding these differences, no one would pick me out of a crowd as likely to have these, or any other differences that make me unique. In the past, several well-meaning but misguided healthcare professionals have told me that I should not have more than a 5th grade vocabulary, that I should have seizures, or that I should have other deficits and limitations. I do not. They seemed disappointed, even angry, that I did not have the limitations they unilaterally pronounced that I should have, without the benefit of any further investigation. I successfully completed college and graduate school, have a vocabulary in the 98th percentile, and learned a foreign language (Russian) well enough that I dreamed in it.

Greta Tuckute, Alexander Paunov, Hope Kean, Hannah Small, Zachary Miner off, Idan Blank, Evelina Fedorenko, 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, 169 (2022) 108184.

Indeed. Except for the advent of fMRI, no one would ever have known about her brain abnormality — a sobering thought when we realize how many definitive judgments are made on the basis of the merely partial understanding that a new technology often provides.

In reality, the human brain is remarkable not only for its complexity but for its adaptations to adversity, especially early in life.

Note: Here’s a preprint of the author’s findings, open access, at bioarXiv.

Here Are some other stories of people living with partial or split brains:

Yes, split brains are weird, but not the way you think. Scientists who dismiss consciousness and free will ignore the fact that the higher faculties of the mind cannot be split even by splitting the brain in half.

Some people think and speak with only half a brain. A new study sheds light on how they do it.

Boy born with 2% of brain does maths, loves science. Noah Wall’s story raises intriguing questions about the relationship between the brain and the mind

and

Four researchers whose work sheds light on the reality of the mind The brain can be cut in half, but the intellect and will cannot, says Michael Egnor. The intellect and will are metaphysically simple.