IT WAS BEDTIME for Krista and Tatiana Hogan, and the 4-year-old twins were stalling. Their grandmother, Louise McKay, who lives with the girls and their parents in Vernon, British Columbia, was speaking to them in soothing tones, but the girls resorted to delaying classics of the toddler repertory. “I want one more hug!” Krista said to their grandmother, and then a few minutes later, they both called out to her, in unison, “I miss you!”
Suddenly Krista reached for a cup with a straw in the corner of the crib. “I am drinking really, really, really, really fast,” she announced and started to power-slurp her juice. Tatiana was, as always, sitting beside her but not looking at her, and suddenly her eyes went wide. She put her hand right below her sternum, and then she uttered one small word that suggested a world of possibility: “Whoa!”
In any other set of twins, Krista’s drinking and Tatiana’s reaction would be an interesting coincidence, but Krista and Tatiana are joined at the head—the medical term is craniopagus, a condition that occurs in one in 2.5 million births. The way the girls’ brains formed beneath the surface of their fused skulls, however, makes them unique in the annals of scientific literature. Their brain images reveal what looks like an attenuated line stretching between the two organs, a piece of anatomy their neurosurgeon, Douglas Cochrane of British Columbia Children’s Hospital, has called a thalamic bridge. The thalamus is a kind of switchboard, a two-lobed organ that filters most sensory input and has long been thought to be essential in the neural loops that create consciousness. Cochrane believes the bridge links the thalamus of one girl to the thalamus of her sister. He and the girls’ other doctors believe it is possible that the sensory input that one girl receives could somehow cross that bridge into the brain of the other. One girl drinks, another girl feels it.
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What actually happens in moments like this is guesswork. No controlled studies have been done on the girls; no advanced imaging technology has been applied to their brains. But a mere glimpse of that line between the two brains has reduced accomplished neurologists to sputtering incredulities. “OMG!!” Todd Feinberg, a professor of clinical psychiatry and neurology at Albert Einstein College of Medicine, wrote in an e-mail. “Absolutely fantastic. Unbelievable. Unprecedented as far as I know.”
Reaching for the cup from which her sister was just drinking, Tatiana started to chug. Krista’s hand flew to her own stomach. “Whoa!” she said. The girls cracked up. Louise sighed. “Girls,” she said one more time. “It is time to settle down.”
THOUGH THEY FREQUENTLY move in near synchrony, the girls have different personalities. Their mother, Felicia Simms, says Tatiana is more lighthearted, that Krista is “more of the bully.” And they look remarkably different, although they are thought to be identical. Tatiana’s heart and kidneys do more of the work for their bodies, so she is smaller than her sister, frailer, diminutive like her fairy namesake; Krista has the round belly and cheeks of a typical preschooler. Krista has a small red birthmark on her chest; Tatiana does not. Krista is allergic to canned corn; Tatiana is not. Even twinship, shared daily experiences, and possibly shared sensory experiences do not render them one and the same.
When the girls were younger, they tried to pull their heads away from each other, Simms told me. “And I would say to them, ‘You can’t do that,’” she said. “I just told them, ‘You girls are stuck. You’re stuck together.’” Sometimes the girls would offer up that information themselves. “I am stuck,” Krista told me one afternoon. She tapped the portion of the head that she shares with her sister. And does she like being stuck? “I love I am stuck,” she said. She smiled. She had the dreamy look of someone romantically infatuated. “I love my lovely sissy,” she said. Later that day, Tatiana announced the same thing, but she sounded more distressed, confused: “I am stuck,” she said, a querulous look on her face. She was a girl sending a message in a bottle, searching for some answer to the essential question of her mysterious, still-forming mind.
Later in the week, Simms was getting Tatiana and Krista dressed for a five-hour van ride to Vancouver, where the girls had a series of doctors’ appointments. Though Krista grabbed initially at a pink hooded sweatshirt, she ceded it easily to Tatiana and settled for the gray. “I am in gray,” she said. “And I am in pink,” Tatiana said. Something about the clear distinction may have rung some bell in Krista’s mind. She looked at her mother. “I am just me,” she said. The sentiment—assertive and profound—was hardly out of her mouth before her sister echoed her. “I am just me,” Tatiana said.
The girls surely have a complicated conception of what they mean by “me.” If one girl sees an object with her eyes and the other sees it via that thalamic link, are they having a shared experience? If the two girls are unique individuals, then each girl’s experience of that stimulus would inevitably be different; they would be having a parallel experience, but not one they experienced in some kind of commingling of consciousness. But do they think of themselves as one when they speak in unison, as they often do, if only in short phrases? Although each girl often used “I” when she spoke, I never heard either say “we.” “It’s like they are one and two people at the same time,” said Feinberg of the Albert Einstein College of Medicine.
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. And yet here are two girls who can possibly feel what the other feels. Even that extraordinary dynamic would still put the girls on the continuum of connectivity that exists between ordinary humans. Some researchers believe that when we observe another person feeling, say, the prick of a pin, our neurons fire in a way that directly mimics the neurons firing in the person whom the pin actually pricks. So-called mirror neurons are thought to foster empathy, creating connections of which we are hardly aware but that bind us in some kind of mutual understanding at a neurological level.
Could the girls’ connection go beyond sensory impressions to higher thoughts, thoughts as simple as “I want water” or as complex as “I’m tired of Goodnight Moon?’’ The family says that the girls often get up silently and suddenly and walk over to, say, a sippy cup, which Tatiana then immediately hands to Krista, who drinks from it. I did not witness any such incident; but if it happens as described, does one girl silently express her thirst to the other in the form of a higher thought? Does Tatiana somehow experience, instead, her sister’s basic sensation of thirst, but recognize it as originating elsewhere? Is the request whispered, inaudible or incomprehensible to anyone but the sister who is so closely linked?
The story of the girls drinking juice in the crib—one girl seeming to feel the other gulp—particularly intrigued Feinberg. “‘I felt Tatiana drink that,’” he said, musing on the idea of it. “Now, how crazy is that? I mean, seriously! This is beyond empathy—it’s like a metasensory experience. It’s like she has one consciousness and can witness another’s.”
AS PROFOUND AS it is to consider that each may witness the other’s consciousness, equally striking is their ability to maintain their individuality. In his book, Altered Egos: How the Brain Creates the Self, Feinberg describes patients with various split-brain syndromes, cases in which the corpus callosum, the part of the brain that connects one hemisphere to the other, is severed. In one manifestation, a patient might find that one of his hands is at odds, or all-out war, with the other. The unruly hand might throw a spoon or tear up money—actions that do not originate with any desire of which the patient is aware. Yet aside from the alien hand, the patient still feels essentially like himself; such patients “act, feel, and experience themselves as intact,” Feinberg writes. Feinberg says the brain labors to create a unity of experience, knitting together our partial selves via numerous cortical mechanisms into a unified whole, into a sense of self.
That the girls each have clear distinction, despite the likely leakage of sensory impressions, was telling to Feinberg. “With the split brain, you essentially cut the brain in half, yet the person feels and acts as a whole,” Feinberg said. “In these girls, they’re linked, yet each acts as a whole. It’s like a force of nature—the brain wants to unify.”
As would be true of any other two sisters, the girls’ relationship to each other and to their unusual connection is unpredictable. Their union could prove, as their grandmother predicts, a model of boundless, blissful empathy. But their lives could also entail a barrage of confused impressions, with each girl having just enough of a sense of self to resent the intrusions of the other’s. Over time, would the girls increasingly tune out each other’s perceptions, with some kind of neural pruning doing the work that surgery could not? Or would some complicated, constant interplay of sensory input and response further fuse their personalities, rendering them ever more like one? Would they have any say in the matter?
THE GIRLS ARE used to showing off their tricks. And they are infinitely proud of the small things they can do that were twice as challenging for them to learn as for someone who moves independently. They like to show how they can jump up and down, which they do like any other children, or climb into their crib, which they do like self-taught gymnasts.
The twins are most moving, however, when they are least aware of how profoundly different they are. One evening, shortly before the girls went to bed, I reached out and touched the tiny birthmark below Krista’s shoulder. “Don’t touch my pen mark,” Krista said. She touched the small dot of red and stroked it with her finger. Her sister, who has no birthmark there, stroked the same spot on her own body, in just the same way, drawing a line downward. She wore the same injured facial expression as her sister.
At bedtime, the two girls seemed more like one than when they first arose, as if the labors of the day steadily eroded whatever barriers separated them. Both girls faced their oversize crib, and then Tatiana started climbing up its side with her feet, using Krista as a kind of bracing post. From there, Krista jumped up to join her sister in her usual way. Once their grandmother quieted the girls, they finally lay down on their backs. Each girl put an inner hand in her mouth, with four bent fingers, then let it fall back to her side. Each held a doll in her outer hand, threw it over her face, and then pulled it away. They sighed simultaneously. Soon Krista was asleep; an instant later Tatiana was as well. They had both flung their inside arms up and over their own eyes, so that they were mirror images of each other at rest. Then Tatiana alone moved her arm away, and the girls drifted off for the night, to dream, together or apart, their secret dreams.
©2011, Susan Dominus. From a longer story originally published in
Used with permission. All rights reserved.
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