I believe it is possible to connect two brains in such a way that their owners share a single conscious state that I call mindmelding. The possibility of mindmelding also forces several interesting changes in the way we conceive of our sense of self, in how our brains represent the world, and in how we speak about the minds of others.
A fascinating recent discovery may shed light on these issues. Krista and Tatiana Hogan are 4-year-old twins who were born conjoined at the head. Images of their brains reveal a bundle of fibers connecting their thalami, an organ at the center of the brain vital for perception and consciousness. Controlled studies are now underway to test the hypothesis that they have “internal” access to each other’s minds, but there are some tantalizing clues that they do. One sister will laugh at a television program only the other can see (their heads are joined in such a way that their fields of view are angled away from each other). Scientists who have examined them believe that sensory information entering through one girl’s eyes is actually split and sent to visual areas in both of their brains.
But, if this is correct, they are not experiencing the same conscious perceptions, because the split has occurred early enough in processing to result in two separate conscious states that are very similar to one another. Thus this provides room for doubt as to whether they are really experiencing each other’s conscious states, as opposed to copies of them, since one can doubt the fidelity of the copy. What if we made the split later in processing, however, so that there was only one conscious percept, which the twins might react to differently? Then they would be experiencing the same conscious perceptual state, even if they react differently to it. If this could happen, the consequences for the age-old debate about the nature of our minds will be huge."