Yes, I know. Not him again. But I’ll make it quick this time. Michael Egnor, neurosurgeon and apologist for the creationist Discovery Institute, has taken umbrage with Jerry Coyne’s interpretation of split brain research. On the DI’s “Mind Matters”blog, Egnor writes:
Like most commentators on this important research, Coyne misunderstands its implications. Split surgery, called commissurotomy by neurosurgeons, is an operation that treats certain kinds of seizures. I’ve performed that operation myself and have taken care of the patients before and after the surgery. Beforehand, they are often incapacitated — they may have 20 or 30 seizures per day. In the surgery, we cut a portion (occasionally all) of the corpus callosum, which is a bundle of fibers that connects the two hemispheres of the brain. This procedure prevents seizures from moving across hemispheres and usually greatly reduces their severity.
What is most remarkable about these patients — what spurred Roger Sperry to do his landmark Nobel Prize-winning research — is that after the surgery they are unaffected in everyday life, except for the diminished seizures. They are one person after the surgery, as they were before. They are basically the same, even after their brain has been functionally cut in half. They feel the same, act the same, and think the same, for all intents and purposes.
In his meticulous research, Sperry found neurological effects from the surgery, but they were subtle. The hemispheres of the brain tend to act independently in some perceptual and motor activities. A patient could only name an object if it is shown to the speech hemisphere (usually the left hemisphere), and could move limbs only in accordance with the hemisphere to which information is presented. All of the disabilities Sperry found were perceptual and motor, not intellectual and abstract.
Michael Gazzaniga, who has been previously mentioned on this blog, was Sperry’s co-investigator on those studies, has continued to expand on this research since Sperry’s death, and is a giant figure in the field of cognitive neuroscience. So, needless to say, it is likely that he has a reasonably good understanding of this research and its implications. This is expounded upon at length in the series of lectures linked in the earlier post, but this video gives a concise summary of the conclusions he draws from his own split brain research:
That is to say, even under normal circumstances (i.e. with an intact corpus callosum), people do not just have dual “consciousness”, but multiple “consciousnesses” (I understand the term “consciousness” is problematic here, hence the scare quotes). There are innumerable computational processes occurring in the brain at any given time, and almost all of this is at a level below our conscious awareness. This information is then filtered and integrated by a region in the left hemisphere Gazzaniga refers to as “the interpreter” and presented to our conscious selves in the form of a coherent narrative.
Split brain patients have provided us an opportunity to peer into this process and dissect its details in a manner that could not have been done otherwise. However, as long as the “interpreter” remains intact and continues to do its job, the individual will continue to experience his own mind as operating as a coherent whole, and present as an intact and normally functioning individual to the outside world. This is why these people do not generally experience or demonstrate obvious disabilities or loss of function after surgery. The changes in neurological functioning will not be evident to a neurosurgeon hurrying through his rounds on the post-op ward, or in the person’s everyday tasks and encounters with other people. However, the changes nonetheless exist and can be demonstrated thru careful neuropsychological investigation.
To be sure, this is not the unanimous opinion of researchers in cognitive neuroscience, but it is a widely held one and certainly one that can be reasonably concluded from the evidence. Nothing about this demands the conclusion that cognitive functioning can only be explained through mysterious, immaterial, supernatural forces.