Wednesday, June 1, 2011

Craniopagus Twins

Last weekend, the New York Times magazine featured a story about a set of four-year-old conjoined twins, Krista and Tatiana Hogan, who, unlike most conjoined twins, are joined at the head. They are craniopagus twins. The author of the piece, Susan Dominus, provides both an anthropological portrait of the girls—she spent five days with the twins and their extended family—and an exploration of the meaning of identity.

What makes Krista and Tatiana's story so fascinating is that the girls appear to share sensory information. One sees something funny on television, for example, and the other laughs. Images of the girls' brains reveal an anatomical link between their thalamuses—a thalamic bridge. "The thalamus is a kind of switchboard," explains Dominus, "a two-lobed organ that filters most sensory input and has long been thought to be essential in the neural loops that create consciousness." The girls' doctors believe that sensory input from one of the girls can cross the thalamic bridge into the brain of her sister.

Dominus reports that she witnessed, over and over again, remarkable sensory connection between the girls. "Over the course of the days I spent with them," she writes, "I witnessed the girls do seemingly remarkable things: say the precise name of the toy that could only be seen through the eyes of her sister or point precisely, without looking, to the spot on her sister’s body where she was being touched." She also saw the girls fight when one of them wanted to eat chicken fingers and the other objected violently because she didn't like the taste.

In short, Krista and Tatiana seem, on some level, to share a mind. This makes them fascinating subjects for neuroscientists. Dominus explains:
The average person tends to fall back on the Enlightenment notion of the self—one mind, with privacy of thought and sensory experience—as a key characteristic of identity. That very impermeability is part of what makes the concept of the mind so challenging to researchers studying how it works, the neuroscientist and philosopher Antonio Damasio says in his book, "Self Comes to Mind." "The fact that no one sees the minds of others, conscious or not, is especially mysterious," he writes. We may be capable of guessing what others think, "but we cannot observe their minds, and only we ourselves can observe ours, from the inside, and through a rather narrow window."
Assuming Krista and Tatiana survive into adolescence and beyond—and I certainly hope they do—neuroscientists will seek to gauge if the girls are able to share abstract thoughts, just as psychologists will be eager to understand how their condition has shaped their identities. For the time being, despite physiological challenges, Krista and Tatiana, Dominus reports, are remarkably well-adjusted children—daily reminding us of the power of the brain.

In addition to reading the full article, I recommend this video about the twins:

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