This pseudo-Paper is intended as the mechanism to record time spent on the Note 'Commissurotomy' during my Thesis research, as from 2011. Click here for Note.
Write-up1 (as at 14/10/2017 23:22:34): Commissurotomy
- A commissurotomy involves cutting the corpus callosum, the bundle of nerve fibres connecting the two cerebral hemispheres of the brain. The procedure is used to treat epilepsy, but is invoked by philosophers as a thought experiment3 (TE) to provide an alleged real-life example of fission4. The real-life situation usually has to be improved to overcome the laterality of the brain, and the two hemispheres are assumed to be idempotent, with nothing of philosophical significance alleged to ride on this idealisation.
- As with all TEs, what we can learn from this one depends on our level of description of what is supposed to be going on. The idea is that each hemisphere fully supports the mental life of the subject(s), and consequently that there is, or can come to be, multiple subjects – and hence multiple persons – within the same human animal. Commissurotomy is used as an objection to animalism5. Some philosophers argue that (for modal reasons) there are always two persons within the same human being.
- Clearly, this is not obviously the case in the normal asymmetric brain (see, no doubt, "Kinsbourne (Marcel) - Asymmetrical Function of the Brain"). So, in these thought experiments – and prior to this idealised idempotency – there has to be a period of equalisation and duplication of function. This sounds like it would lead to causal over-determination, but maybe the way it could be described is as with fault-tolerant computer systems, so that one hemisphere always takes the lead (or maybe they alternate) – in fact, this is said to be the case [where6?] with marine mammals, to enable them to sleep without drowning. The non-dominant hemisphere is just kept up to date – either continuously or periodically – with whatever data and current state is represented in the dominant hemisphere. In such a situation, there are already – prior to the commissurotomy – two exactly similar (other than that they are mirror images of one another) but non-identical half-brains.
- Of course, the last sentence above begs some questions. It is only the cerebral hemispheres that are separated and duplicated – but they are still physically connected via the brain-stem – even if the logical connections are greatly reduced. It is said (where7?) that severed hemispheres can still communicate with one another via cues passed externally to the brain. Indeed, the case of the dicephalus8 suggests that this co-ordination is possible with two complete brains, where the hands can be coordinated to drive a car and even type, despite being controlled by different brains.
- A recent paper - "Pinto (Yair) - When you split the brain, do you split the person?" - has suggested that the research for which Sperry received a Nobel Prize has not been replicated – in the case of two patients – and that this raises questions about the nature of consciousness. I have my doubts. Might the corpus collosi not have been entirely severed in these cases, or might one of the above situations apply?
- A reading list (where not covered elsewhere) might start with:-
- "Baillie (James) - Commissurotomy and the Unity of Mind", Baillie
- "Davis (Lawrence H.) - Cerebral Hemispheres", Davis
- "Dewitt (Larry W.) - Consciousness, Mind, and Self: The Implications of the Split-Brain Studies", Dewitt
- "Eccles (John) - Mental Dualism and Commissurotomy", Eccles
- "Gillett (Grant) - Brain Bisection and Personal Identity", Gillett
- "Glover (Jonathan) - Split Brains", Glover
- "Greenwood (John) - Split-Brains and Singular Personhood", Greenwood
- "Hershenov (David) & Taylor (Adam P.) - Split Brains: No Headache for the Soul Theorist", Hershenov+Taylor
- "Hirsch (Eli) - Divided Minds", Hirsch
- "Iredale (Mathew) - Your Two Brains", Iredale
- "Liao (S. Matthew) - The Organism View Defended", Liao9
- "MacKay (Donald) - Divided Brains - Divided Minds", MacKay
- "Marks (Charles) - Commissurotomy, Consciousness and Unity of Mind", Marks
- "Tye (Michael) - Split Brains", Tye
- "Van Inwagen (Peter) - Two Problems About Personal Identity: Memory and Commissurotomy", van Inwagen
- "Wilkes (Kathleen) - Consciousness and Commissurotomy", Wilkes
- This is mostly a place-holder10. Currently, just see the categorised reading-list.
- This is the write-up as it was when this Abstract was last output, with text as at the timestamp indicated (14/10/2017 23:22:34).
- Link to Latest Write-Up Note.
- A number of my philosophical Notes are “promissory notes” currently only listing the books and papers (if any) I possess on the topic concerned.
- I’ve decided to add some text – whether by way of motivation, or something more substantive – for all these identified topics related to my Thesis.
- As I want to do this fairly quickly, the text may be confused or show surprising ignorance.
- The reader (if such exists) will have to bear with me, and display the principle of charity while this footnote exists.
Text Colour Conventions (see disclaimer)
- Blue: Text by me; © Theo Todman, 2018