If someone becomes a split-brain patient, which side will "maintain" the continuity in their consciousness?

Question

The brain injury might apparently produce two "independent" consciousnesses, and I'm wondering where the original person's "consciousness" would "transfer".

We had a debate on this over at Reddit some time ago, but it didn't really get resolved. What's more important is that Christof Koch (one of the top researchers in the field) explicitly said that splitting the corpus calloseum would produce two conscious minds in one skull.

About two hundred million fibers that keep the two cortical hemispheres in constant communication. These are cut in split-brain patients, creating two conscious minds in one skull.

Answer 1

If by continuity you mean, "a feeling that I am who I was before the operation, (perhaps with some changes)", then it seems that each hemisphere would separately maintain continuity, in the same way patients after massive strokes and other sudden brain injuries don't usually feel "they are a different person".

Research by Turk et al. (2003) suggests it's just the left hemisphere, because only the left hemisphere has the 'interpreter' module.

However, other research by Turk et al. (2002) find that both hemispheres of a split brain patient recognize his own face, similar to Sperry et al. (1979). I think these face recognition tests tell us less about the 'feeling of self' than tests of access to autobiographical memories before the operation, and their emotional content, but I couldn't find any such studies.

A good review of the field instead was done by Uddin in 2011.

Sperry, R. W., Zaidel, E., & Zaidel, D. (1979). Self recognition and social awareness in the deconnected minor hemisphere. Neuropsychologia, 17(2), 153–166. doi:10.1016/0028-3932(79)90006-X

Turk, D. J., Heatherton, T. F., Kelley, W. M., Funnell, M. G., Gazzaniga, M. S., & Macrae, C. N. (2002). Mike or me? Self-recognition in a split-brain patient. Nature Neuroscience, 5(9), 841–842. doi:10.1038/nn907

Turk, D. J., Heatherton, T. F., Macrae, C. N., Kelley, W. M., & Gazzaniga, M. S. (2003). Out of Contact, Out of Mind. Annals of the New York Academy of Sciences, 1001(1), 65–78. doi:10.1196/annals.1279.005

Uddin, L. Q. (2011). Brain connectivity and the self: The case of cerebral disconnection. Consciousness and Cognition, 20(1), 94–98. doi:10.1016/j.concog.2010.09.009

Answer 2

The fact that these people don't exhibit a lot of change in behavior, and report no real difference after the operation (other than in contrived tests) suggests that our idea of a single conscious "self" is simply wrong.

This sort of question is probably never going to be answered to anyone's satisfaction, any more than you could answer questions about what happens if your brain is duplicated on a computer, or your body is destroyed and then recreated by a Star Trek transporter. Is your consciousness continuous after Scotty beams you up, or is it a completely new mind with copies of your memories, and your old self died back on the surface of the planet?

I don't think in any of these cases there is really a coherent question, but it only seems like it is. Our brain has a built in concept of "self" that is core to our thought process, necessarily so. A manmade autonomous vehicle would have the same -- it has to model it's environment, and must include itself in that model, but with appropriate differences, based on the fact that it controls itself in ways it doesn't control other things.

I think what is happening with this sort of question is that it is exploiting our tendency to erroneously assign a sort of tangibility to the idea of self, that extends beyond the actual context or perspective where it makes sense.

Answer 3

Consciousness research in Neuroscience is relatively new, so there isn't yet any consensus on how consciousness works precisely (or an agreed upon definition).

My understanding is that the current majority view is that consciousness is distributed throughout the brain (while I can't track down a reference), so transecting the Corpus Callosum won't "transfer" consciousness anywhere, it will remain everywhere, though presumably a little less coherent after the split. Keep in mind that there are many other pathways between the hemispheres besides the Corpus Callosum - such as thalamocortical circuits, those via the midbrain and brainstem and of course external sensorimotor feedback.

I agree with @rob - in that the question can't be answered satisfactorily now, though I think it can be once interpreted in the context of a future concrete definition of "consciousness" and an understand of its mechanisms.

Answer 4

The question:

I'm wondering where the original person's "consciousness" would "transfer"

Presupposes a Cartesian Ego; or the idea that consciousness is something separate, ethereal, and indivisible. I recommend reading some Daniel Dennett and Derek Parfit to cure yourself of this common assumption; a good philosophical starting point is Parfit's "Reasons and Persons". Alternatively, if you want a more pop-philosophy/science treatment of the issue, consider Chapters 15 and 21 of Hofstadter's "I am a Strange Loop". In particular, pay close attention the the teletransporter intuition-pump.

Most neuroscientists (Christof Koch included) would find the cartesian ego assumption to be very naive. Thus, this whole discussion would be a pseudo-question for them. There is no indivisible units of "consciousness" to be transferred. To many non-dualists, consciousness is a folk psychology concept, that when pushed to the limit (such as the teletransporter examples, or perfect split-brain patients) becomes ridiculous. Much like conservation-of-mass (or Galilean transformation) is a good principle of folk physics (and classical mechanics), that becomes ridiculous when you move to the relativistic setting where you need to use mass-energy (or Lorentz transformation). There is no reason to believe your everyday intuition about concepts (be they physics or psychology) should hold in very strange settings that you have never come close to experiencing.

Answer 5

If only a small part of the corpus callosum is cut then the patient will still have only one main consciousness, but if too much of the corpus callosum is removed then consciousness will split in two.

Split brain surgery performed in early childhood may initially split the brain into two separate consciousnesses, but as the other connections between the hemispheres rewire there will eventually come a point where the brain as a whole integrates more information than each hemisphere does separately, and the two consciousnesses will recombine into one.

People born with agenesis of the corpus callosum rarely show any sign of having 'split consciousness'.

Ettlinger, G., Blakemore, C. B., Milner, A. D., & Wilson, J. (1972). Agenesis of the corpus callosum: A behavioural investigation. Brain: A Journal of Neurology, 95(2), 327-346. http://dx.doi.org/10.1093/brain/95.2.327

Sauerwein HC, Lassonde M. (1997) Neuropsychological alterations after split-brain surgery. J Neurosurg Sci. 41(1):59-66.