Krista and Tatiana Hogan are conjoined twins who have directly connected brains, born in 2006.

Here’s a pretty good documentary about them, made at the age of 7.

And here’s a paper (in an undergrad journal) that considers some of the implications.

Craniopagus twins, who are conjoined at the head, are uncommon and often misunderstood. While craniopagus is rare in itself, Krista and Tatiana Hogan are unique even among craniopagus twins: their brains are connected…Consequently, Krista and Tatiana are left with a connection that is both novel to documented research and exquisitely mysterious. They possess what their pediatric neurosurgeon Dr. Doug Cochrane has called a “thalamic bridge” (Dominus, 2011a). Krista and Tatiana’s thalamic bridge will provide significant insight into the study of cognition and behaviour, and may even have significant implications to the philosophy of mind. Furthermore, their connection will be accompanied by major social change, as we must redefine our definition of what it means to be an individual. For us to understand how being part of a pair is more important than being an individual to one’s identity, we must shift our perspective and eliminate our preconceived notions of individuality.

Craniopagus: Overview and the implications of sharing a brain | Squair | University of British Columbia’s Undergraduate Journal of Psychology

[It won’t be so long before we can connect brains technologically, so it’s extremely interesting to see how that might turn out in practice. -egg]