What One Sister Tastes, the Other Sometimes Knows

They were born in Vancouver on October 25, 2006, joined at the skull.

Craniopagus twins — fused at the head — are already among the rarest of conjoined births. Tatiana and Krista Hogan are rarer still. Inside one continuous cranium sit two brains linked by a band of tissue doctors call a thalamic bridge: a connection between the thalamus of one girl and the thalamus of the other. The thalamus is a relay. Sensory and motor signals pass through it. In these sisters, some of those signals appear to cross.

Tests described by clinicians at BC Children’s Hospital and later in CBC documentaries showed visual activity in one twin’s cortex when the other looked at an image. Family and researchers have reported shared taste and touch as well — Krista biting a pickle, Tatiana grimacing; a stimulus on one body answered in the other. Motor control is unevenly shared: one girl can move limbs that, on a diagram, belong to her sister. The twins have said they sometimes “talk in our heads.” Scientists treat that claim with more caution than the sensory findings. It is reported. It is not a completed map of two minds.

Separation was judged too dangerous. Shared vessels and the bridge itself made cutting them apart a likely sentence, not a cure. Their mother, Felicia Simms, and the family in Vernon, British Columbia, raised them as two children who happen to live in one architecture. They learned to walk, talk, go to school. They argue. They prefer different foods. They also laugh at the same moment without a word.

Neuroscience has used their scans to ask old questions with new wiring: Where does one self end? How much of sight is private? The girls themselves have treated the mystery as a Tuesday. They are not a thought experiment. They are sisters who can, in documented ways, borrow a glimpse, a flavor, a flinch — and who have grown up insisting they are still two.

Sources

CBC Docs POV, Inseparable (features on Tatiana and Krista Hogan and the thalamic bridge)
Vancouver Magazine, “The World’s Rarest Twins,” and contemporaneous reporting with pediatric neurosurgeon Dr. Douglas Cochrane
Maclean’s / CBC Radio features on shared vision, taste, and development (2011–2014)
Wikipedia compilation of published medical and documentary accounts: Krista and Tatiana Hogan