- This pseudo-Paper is intended as the mechanism to record time spent on the Note 'Commissurotomy1' during my Thesis research, as from 2011.
- For the actual time recorded, click on "Paper Summary" above.
Write-up2 (as at 24/06/2018 16:32:10): 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 experiment4 (TE) to provide an alleged real-life example of fission5. 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 animalism6. 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 [where7?] 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 (where8?) that severed hemispheres can still communicate with one another via cues passed externally to the brain. Indeed, the case of the dicephalus9 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?
- For a page of Links10 to this Note, Click here.
- Works on this topic that I’ve actually read11, include12 the following:-
- "Benson (Ophelia) - This Isn't My Body", Benson
- "Liao (S. Matthew) - The Organism View Defended", Liao13
- "Marks (Charles) - Commissurotomy, Consciousness and Unity of Mind", Marks
- "Olson (Eric) - Why We Need Not Accept the Psychological Approach", Olson
- "Shoemaker (David) - Personal Identity and Immortality", Shoemaker
- "Van Inwagen (Peter) - Précis of Material Beings", van Inwagen
- "Wilkes (Kathleen) - Being in Two Minds", Wilkes
- 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
- "MacKay (Donald) - Divided Brains - Divided Minds", MacKay
- "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-holder14.
- This is the write-up as it was when this Abstract was last output, with text as at the timestamp indicated (24/06/2018 16:32:10).
- 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.
- If only a “non-updating” run has been made, the links are only one-way – ie. from the page of links to the objects that reference this Note by mentioning the appropriate key-word(s). The links are also only indicative, as they haven’t yet been confirmed as relevant.
- Once an updating run has been made, links are both ways, and links from this Notes page (from the “Authors, Books & Papers Citing this Note” and “Summary of Note Links to this Page” sections) are to the “point of link” within the page rather than to the page generically. Links from the “links page” remain generic.
- There are two sorts of updating runs – for Notes and other Objects. The reason for this is that Notes are archived, and too many archived versions would be created if this process were repeatedly run.
- Frequently I’ll have made copious marginal annotations, and sometimes have written up a review-note.
- In the former case, I intend to transfer the annotations into electronic form as soon as I can find the time.
- In the latter case, I will have remarked on the fact against the citation, and will integrate the comments into this Note in due course.
- My intention is to incorporate into these Notes comments on material I’ve already read rather than engage with unread material at this stage.
- I may have read others in between updates of this Note – in which case they will be marked as such in the “References and Reading List” below.
- Papers or Books partially read have a rough %age based on the time spent versus the time expected.
Text Colour Conventions (see disclaimer)
- Blue: Text by me; © Theo Todman, 2018