Tatiana and Krista Hogan of British Columbia are twin 4-year-olds who are joined at the skull. They are too young for thorough testing, but they have given hints that they share some information between their brains!
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.
The New York Times magazine has an extensive article on Tatiana and Krista, covering their lives, medical condition, and the very rare opportunity they may present to learn about how the human brain works. Link | video (Image credit: Stephanie Sinclair/VII, for The New York Times)
Great story. Feinberg would know he wrote the book [on it] Altered Egos: How The Brain Creates The Self which is an excellent read btw.
While the thalamus is involved in consciousness it is more accurately the cortico-thalamic complex. That is the meshwork of reentrant mapping between the thalamus and the neo-cortex (particularly the frontal lobes). This may explain that although they share some information they maintain different perspectives and preferences. A complete assimilation into one self has not occurred, although one might suspect an internal struggle of them to maintain their own identities. They are young still and a lot can change to tie them closer together or perhaps separate them (neurologically).