At some point, one of the two circles would fill with randomly oriented stripes for just 50ms (one twentieth of a second) and afterwards the participants were asked to say which direction the stripes were pointing in.
[…] Twins joined at the head — the medical term is craniopagus — are one in 2.5 million, of which only a fraction survive. The way the girls’ brains formed beneath the surface of their fused skulls, however, makes them beyond rare: their neural anatomy is unique, at least in the annals of recorded 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, because he believes it links the thalamus of one girl to the thalamus of her sister. 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. Because the thalamus functions as a relay station, the girls’ doctors believe it is entirely 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.
What actually happens in moments like the one I witnessed is, at this point, theoretical guesswork of the most fascinating order. No controlled studies have been done; because the girls are so young and because of the challenges involved in studying two conjoined heads, all the advanced imaging technology available has not yet been applied to their brains. Brain imaging is inscrutable enough that numerous neuroscientists, after seeing only one image of hundreds, were reluctant to confirm the specific neuroanatomy that Cochrane described; but many were inclined to believe, based on that one image, that the brains were most likely connected by a live wire that could allow for some connection of a nature previously unknown. A mere glimpse of that attenuated line between the two brains 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.” A neuroscientist in Kelowna, a city in British Columbia near Vernon, described their case as “ridiculously compelling.” Juliette Hukin, their pediatric neurologist at BC Children’s Hospital, who sees them about once a year, described their brain structure as “mind-blowing.”
“Now I do it,” Tatiana said, reaching for the cup from which her sister was just drinking. She 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.”
[…] By the time she [Felisha Simms] delivered, the doctors were preparing her for the worst; social workers met with her about grief counseling. But Simms’s intuition was right: the twins were born healthy at 34 weeks, miraculously stable and in need of no major interventions. The girls stayed under observation at the hospital for two months, and soon Simms and Hogan faced another major decision — whether or not to separate them.
Cochrane, their neurosurgeon, consulted with other surgeons who have separated conjoined craniopagus twins, and the team concluded, based on their experience with that kind of surgery and their analysis of the CT scans, that separation would be extremely high risk.
“You’d have to have cut through too much normal tissue and split the thalami,” said James T. Goodrich, director of pediatric neurosurgery for Children’s Hospital at Montefiore in the Bronx who was consulted on the case. “It would have potentially been lethal.”
Although Tatiana does bear more of the burden of pumping blood for their two bodies, the vascular system is symmetrical enough that the doctors consider them relatively healthy. (Given the risks, the family opted not to separate the girls.)
From the very beginning, doctors wondered if the twins shared sensation; an early video shows one girl being pricked for a blood test as the other starts to cry, her face a perfect mirror image of her sister’s. A pacifier in one mouth seemed to soothe both crying babies.
Despite the interest of the scientific community, the girls, because of their age, have not experienced extensive investigation. “If one of them needs it for their health, by all means, they can do what they need to do,” said their step-grandfather, Doug McKay, who, like their grandmother, is very involved in the girls’ care. “But I’ll be damned if you’re going to poke and prod and experiment on them.”
‘I have two pieces of paper,” Krista announced. The girls sat at a small table in the living room, drawing, their faces, as always, angled away from each other. Each had one piece of paper. So I was surprised by Krista’s certainty: She had two pieces of paper? “Yeah,” the girls affirmed in their frequent singsong unison, nodding together. It was one of those moments that a neurologist or psychologist or any curious observer could spend hours contemplating. Was Krista using “I” to refer to both her and her sister? Is Tatiana agreeing with her sister’s assessment at a cognitive level or uttering the same word simultaneously for reasons unknown to her?
Although the girls can run, play peekaboo, engage in finger play shoot’em-ups for 20-minute marathons and covet their older sister’s Zhu Zhu pets, they are both also developmentally delayed by about one year. Their delays do not surprise their doctors, given their unusual brains and the fact that the girls have been forced to develop skills other children have not.
A crayon drops to the floor, and I move to pick it up, imagining how laborious it would be for them to move away from the table as one, with Tatiana leaning awkwardly to allow her sister to crouch to the ground. When I reach for it, however, the crayon is not there. It is already in Krista’s hand, as if by magic. “My foot do it!” she tells me. Neither girl could draw the letter X, but if there were a standardized test for grasping with toes, the Hogan twins would surely come up in the 99th percentile.
The girls’ brains are so unusually formed that doctors could not predict what their development would be like: each girl has an unusually short corpus callosum, the neural band that allows the brain’s two cerebral hemispheres to communicate, and in each girl, the two cerebral hemispheres also differ in size, with Tatiana’s left sphere and Krista’s right significantly smaller than is typical. “The asymmetry raises intriguing questions about whether one can compensate for the other because of the brain bridge,” said Partha Mitra, a neuroscientist at Cold Spring Harbor Laboratory, who studies brain architecture. The girls’ cognition may also be facing specific challenges that no others have experienced: some kind of confusing crosstalk that would require additional energy to filter and process. In addition to sorting out the usual sensory experiences of the world, the girls’ brains, their doctors believe, have been forced to adapt to sensations originating with the organs and body parts of someone else.
As fantastic as it sounds, there is little doubt in Cochrane’s mind that the girls share some sensory impressions. When they were 2 years old, he performed a study in which Krista’s eyes were covered and electrodes were glued to her scalp. While a strobe light flashed in Tatiana’s eyes, Krista was emitting a strong electric response from the occipital lobe, which is where images are assembled. The test also worked when the girls switched roles. The results were not published, and some neuroscientists believe that this kind of test, which measures changes in brain activity beneath the skull, is imprecise in determining what region of the brain is at play; but most would agree that any response in the other twin’s brain suggests, at a minimum, connectivity.
The explanation Cochrane proposes is surprisingly straightforward for so unusual an outcome: that visual input comes in through the retinas of one girl, reaches her thalamus, then takes two different courses, like electricity traveling along a wire that splits in two. In the girl who is looking at the strobe or a stuffed animal in her crib, the visual input continues on its usual pathways, one of which ends up in the visual cortex. In the case of the other girl, the visual stimulus would reach her thalamus via the thalamic bridge, and then travel up her own visual neural circuitry, ending up in the sophisticated processing centers of her own visual cortex. Now she has seen it, probably milliseconds after her sister has.
The results of the test did not surprise the family, who had long suspected that even when one girl’s vision was angled away from the television, she was laughing at the images flashing in front of her sister’s eyes. The sensory exchange, they believe, extends to the girls’ taste buds: Krista likes ketchup, and Tatiana does not, something the family discovered when Tatiana tried to scrape the condiment off her own tongue, even when she was not eating it.
Even knowing about the tests and what Cochrane believed, I listened to the family’s stories with some amount of skepticism. Perhaps they were imagining it or exaggerating for the sake of a good story. Then in one of the many idle moments of the five days I spent with the family, the girls were watching television, and I absent-mindedly gave Tatiana’s foot, which Krista could not see, a little tickle. She turned to me and smiled, and then Krista spoke: “Now do me,” she said. Had she felt the sensation but wanted the emotional experience of knowing that she, too, was receiving that kind of playful attention?
On another day, Simms picked up a thermometer that had been left on the kitchen table and, just for fun, placed it in Krista’s mouth. Almost immediately, Tatiana got a distant look in her eyes. “Not in mouth,” she said, sounding angry. Then she was quiet, and her focus seemed to tack hard. Her tongue, visible in her half-open mouth, was moving in an unusual way, curling. I wondered if I was imagining something. But Rosa, her 8-year-old sister, noticed it, too.
[..] When the girls wanted to wash their hands in the sink, they worked as one, silently, to drag the bench over to the bathroom. More often than not, they both seemed to want to slither like snakes at the same moment, to roll a ball down a ramp to the television room, to drift toward the electric piano. But acceptance, rather than mutual desire, might be at play: the family often reminds them they have no choice but to compromise, and Simms believes they have a private logic for determining whose turn it is to decide their whereabouts.
[…] Though they frequently move in near synchrony, mirroring each other’s gestures, the girls clearly have different personalities. Simms says Tatiana is more lighthearted, that Krista is “more of the bully” — that she is moved to scratch or hit Tatiana in frustration more often than the reverse. 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 than Krista’s do, so she is smaller than her sister, frailer, diminutive like her fairy namesake; Krista has the round belly and cheeks of many a preschooler. Krista has a small dot of a 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 used to try 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, pausing as she and her sister made their way back to the bathroom, where they wanted to play with the faucets. 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. […]
Later in the week, Simms was getting Tatiana and Krista dressed for a five-hour van ride on treacherous roads in the snow to Vancouver, where the girls had a series of doctors’ appointments. This time there was no fighting over the two different sweatshirts. On the rare occasions when the girls do fight, it’s painful to watch: they reach their fingers into each other’s mouths and eyes, scratching, slapping, hands simultaneously flying to their own cheeks to soothe the pain.
That morning, even though Krista grabbed initially at the pink hooded sweatshirt, she ceded it easily to Tatiana, and Krista 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? When their voices joined together, I sometimes felt a shift — to me, they became one complicated being who happened to have two sets of vocal cords, no less plausible a concept than each of us having two eyes. Then, just as quickly, the girls’ distinct minds would make their respective presences felt: Tatiana smiled at me while her sister fixated on the television, or Krista alone responded with a “Yeah?” to the call of her name.
Although each girl often used “I” when she spoke, I never heard either say “we,” for all their collaboration. It was as if even they seemed confused by how to think of themselves, with the right language perhaps eluding them at this stage of development, under these unusual circumstances — or maybe not existing at all. “It’s like they are one and two people at the same time,” said Feinberg, the professor of psychiatry and neurology at Albert Einstein College of Medicine. What pronoun captures that?
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.”
And yet here are two girls who can possibly — humbly, daily — feel what the other feels. Even that extraordinary dynamic would still put the girls on the continuum of connectivity that exists between ordinary humans. […]
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 ‘Good Night 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 serves as a bridge connecting 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, a consistent feeling of individuality and agency.
That the girls each have clear distinction, despite what he considers to be 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.”
[…] When the girls were younger, each experienced several seizures, which medication has since controlled. At an appointment with Hukin, their neurologist, she asked if they had any episodes recently (they had not, in more than a year), then performed a few quick tests. She put a red crayon in front of Tatiana, a purple one in front of Krista, then asked them to name the color. “Blue,” Tatiana said. “Red,” Krista said. Did they simply not know their colors? “They’re switching them,” their grandmother said; Hukin agreed it was a possibility. Hukin pulled a stuffed animal out of a bag, a turkey, and handed it to Tatiana on her right side, so that Krista could not see. “Krista, do you know what Tatiana has in her hand?” she asked. Krista paused. “Robin?”
Hukin, at the time, said nothing more than “very good.” But she considered this close-enough answer extraordinary, she later told me, and took it as clinical support for the sensory connection that Cochrane’s EEG tests had revealed.
Over the course of the days I spent with them, 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. But other times, the theoretical connection seemed to fail them. The family believes that making the effort to “tune in” sometimes tires them out. It’s possible that they are developing in such a way that their brains are trying hard to filter out input that originates from the other girl’s body.
[…] As I watched the girls negotiate their occasionally conflicting impulses at dinner, I thought of how my friend Peter Freed, a neuroimager and assistant professor of clinical psychiatry at Columbia, explained their possible experience of each other: “It’s as though the secretaries of Goldman Sachs and Lazard Frères have decided, without their bosses’ permission, to share certain visitors and executive memos with each other.” The executives in charge — the parts of the brain more directly involved in decision-making — would inevitably become frustrated. Every time that executive next door makes a decision, the results are “subtly influencing or altering the information the other has to work with,” says Freed, who also writes a blog called Neuroself about the construction of the self in the brain.
[…] 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.
It seemed to me that at bedtime, the two girls were more like one than when they first arose, as if the labors of the day steadily eroded whatever barriers separated them. Sometimes Krista, the physically stronger of the two, seemed to morph before my eyes, no longer one of two, but instead, a sturdy girl carrying around an elaborate appendage she considered part of herself. Perhaps, in submitting, Tatiana felt a kind of relief, the kind we all feel when we cede control to someone we trust. But I also felt a sense of loss — where was Tatiana in all her totality in those moments?
The night I watched them doze off, both girls faced the bed, 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 the usual way. Once their grandmother quieted the girls down in their oversize crib, 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.
