Saturday, August 24, 2013

Split Brain Patients and Organization of the Brain

Commissurotomy or split-brain patients have helped scientists understand the lateralization of the brain; that the right and left halves of the brain are different and provide the ability to function for different tasks. Additionally, it has raised questions as well as provided insight into how and where in the brain individuals maintain a sense of self (Uddin, 2011). Split brain patients have had a portion or the entirety of their corpus callosum surgically severed (Breedlove, Watson, & Rosenzweig, 2010). From studying these individuals, it becomes apparent that each hemisphere has varying responsibility in "cognitive, perceptual, emotional, and motor activities" (Breedlove et al., 2010, p. 605). For example, when words are presented to the left visual field of split-brain patients, the words cannot be repeated verbally (Breedlove et al., 2010). It becomes evident that when the corpus callosum is severed, the two brain halves do not function in tandem, but separately, although not like conjoined twins.

 Similarities and Differences: Split Brain Patients and Conjoined Twins  
Conjoined craniopagus twins are quite rare and can be connected at different parts of the head and brain (Sudha, Dev, Kamble, & Joseph, 2009). For Tatiana and Krista, they shared the thalamus, which is a control center for the brain (MacQueen, 2011). All craniopagus twins share at least a part of the brain, and split brain patients work at trying to share two halves of one brain. Further, some types of conjoined twins and split brain patients may experience two minds sharing one body.

On the other hand, some conjoined twins have two distinct brains and the two work together to make their shared body perform correctly. This is the case with the Hensel twins who basically, share a body but have separate heads and brains (Wallace & Doman, 1996: Weathers, 2007). Split-brain patients may not be as fortunate in that the two halves of their brains may not work together at all, leaving the individual with a less than definitive sense of self. Conjoined twins, with separate brains are able to communicate with each other and this is the primary and most distinct loss caused by a commissurotomy. After this procedure, the two halves of the brain lose the ability to function as one because of the brain's inability to communicate with its other half. Further, most of the time, split-brain patients are the result of a surgical intervention, however conjoined twinning is a natural, albeit rare, occurance.

The Meaning of Personhood

At first I thought about the words of Rene Descartes, 'I think, therefore I am'. Then, however, I thought about some of my severely developmentally delayed clients with little to no ability to cognitively process, let alone engage in a conscious and complex self-perception. Yet, no one would dare say they are not people. So, even the act of thinking does not a person make. That said, it is provocative to read and think about the discussion of conjoined twins and split brain patients and what it means to be a person. It certainly initiates conversation about the singularity of personhood (Greenwood, 1993). Additionally, it raises questions about the existence of sense of self and the role of the brain in that perception. Even the idea of personhood necessitating a sense of self is not sufficient, for a sense of self can be lacking in severely intellectually disabled individuals, but they are still people.

Perhaps one of the most interesting questions raised in the discussion of split-brain patients and conjoined twins are those that question the almost arcane nature of the brain. It can become separate enough in split-brain patients to render an individual uncertain of his or her personhood. And yet, a brain can share one small part in conjoined twins that somehow facilitates an almost extra sensory ability for one twin to perceive something through the eyes of the other.


Greenwood, J. D. (1993). Split-Brains And Singular Personhood [Abstract]. The Southern Journal of Philosophy, 31(3), 285-306. doi: 10.1111/j.2041-6962.1993.tb01722.x  MacQueen, K. (2011). Tatiana and Krista go to school. Maclean’s, 124(39), 26–27.

Norton, A., Zipse, L., Marchina, S. & Schlaug, G. (2009). Melodic intonation therapy: shared insights on how it is done and why it might help. Annals of the New York Academy of Sciences, 1169, 431–436.
Peterson, G. R. (2004). Do Split Brains Listen to Prozac?. Zygon: Journal of Religion & Science, 39(3), 555-576. doi:10.1111/j.1467-9744.2004.t01-1-00601.x.

Sudha, L., Dev, B., Kamble, R., & Joseph, S. (2009). Role of biplane digital subtraction angiography, and 3D rotational angiography in craniopagus twins: A case report, detailed pictorial evaluation, and review of literature. Journal of Pediatric Neurosciences, 4(2), 113–116.
Uddin, L. Q. (2011). Brain connectivity and the self: The case of cerebral disconnection. Consciousness and Cognition, 20(1), 94–98.

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