Brain-Brain communication

On the other hand, we know the brain does have specific modules (such as the visual cortex among many others), which makes an interesting dichotomy.

Actually, all that I've read about the visual cortex leads me to conclude that is just as generic as any other patch of cortex. It becomes visually specific only as a result of being fed visually specific information. In a congenitally blind person, the same patch of cortex will learn entirely other pattern processing functions.

David Carmel, a cognitive neuroscientist at New York University, suggested that even when the girls deliver right answers, the phenomenon could be explained by something other than a neural bridge. “If they’re really close, through minute movements that one makes — maybe a typical movement her sister cannot see, but can feel — the other sister intuits the association. Maybe she associates her sister’s reaction with a robin they once liked, not a turkey.” The connection then might be scientifically mundane, but a marvel nonetheless to the casual observer.

Epistemic caution recommended.

It doesn't have specific modules for 'Left Hand', 'Right Hand', etc. Rather, it takes in information and makes sense out of it. It does this even when the setup is haphazard (as the connection between the twins' brains must be). On the other hand, we know the brain does have specific modules (such as the visual cortex among many others), which makes an interesting dichotomy.

This depends on how you interpret the term "module". One could say that once the brain starts to receive a specific type of information, it begins to form a module for that type of information.

Note that the notions of "modularity" and "adapts to environmental inputs" are not mutually exclusive in any way. As an analogy, consider embryo development. An embryo starts out as just a single cell, which then divides into two, the two of which divide into four, and so on. Gradually the cells begin to specialize in various directions, their development guided by the chemical cues released by the surrounding cells. The cells in the developing fetus / embryo respond very strongly to environmental inputs in the form of chemical cues from the other cells. In fact, without those cues, the cells would never find their right form. If those environmental cues direct the cells' development in the right direction, it will lead to the development of a highly modularized system of organs with a heart, liver, lungs, and so on. If the environmental cues are disrupted, the embryo will not develop correctly.

Now consider the brain. Like with other organs, we start off with a pretty unspecialized and general system. Over time, various parts of it grow increasingly specialized as a result of external outputs. Here external outputs are to be understood both as sense data coming from outside the brain, and the data that the surrounding parts of the brain are feeding the developing part. If the part receives the inputs that it has evolved to receive, then there's no reason why it couldn't develop increasingly specialized modules as a response to that input. On the other hand, if it doesn't receive the right inputs during the right parts of its development, the necessary cues needed to push it in a specific direction will be missing. As a result, it might never develop that functionality.

Obviously, the kinds of environmental inputs that a brain's development should be expected to depend on are the ones that have been the most consistently recurring ones during our evolution.

All of that being said, it should be obvious that "the brain takes in information and makes sense out of it" does not imply "the brain doesn't have specific modules for 'Left Hand', 'Right Hand', etc". In individuals who have developed in an ordinary fashion, without receiving extra neural inputs from a conjoined twin, the brain might have developed specific modules for moving various parts of the body. In individuals who have unexpectedly had a neural link to another brain, different kinds of modules may have developed, as the neural development was driven by different inputs.

Let the flensing begin...

That's amazing, and a pleasant surprise that they're living such a normal life. I really want to read a follow-up article when the girls are old enough to give detailed descriptions of their introspection. I'm aiming for a career in neuroscience, hopefully touching on BCI or uploading, so this is especially interesting.

I am most curious as to what happens if you just went and set up a basic link between two people. Pick up and send signals between brains with something like a cross between one of those nifty move-a-mouse-with-your-brain gizmos (I'm sure it has a more sophisticated name I'm not aware of) and a hearing implant. Has anyone actually tried that before? I have no idea if it actually works like that. I hope it does, because that sounds like a crazy idea I'd actually want to volunteer for. Low bandwidth seems better than no bandwidth at all.

... That makes me wonder if, more within the realm of definite possibility, anyone's ever thought of making a blue-tooth enabled hearing implant. Maybe you could stick your "ear" somewhere else and eavesdrop. Or have multiple ears. Could your brain learn how to interpret direct 5-point surround sound?

EDIT: OKAY, just read up some and realized that is DEFINITELY not how hearing implants work. I thought they were more brain-direct. Ah well, a cochlear mp3 player would still be cool in mono :-)

Why do you think there is a bandwidth problem? Neural transmission is notoriously slow (10m/s linear speed, much slower if not myelinated, about 1ms per pulse, mostly FM encoded). Surely 1kHz, 1ms latency per fiber is not that bad?