8
S plitting B rain &
The
Consciousness
Editor’ s Note:
Harry knocks it out of the park again, with an enthralling article, on the interesting concept of consciousness, relating to evidence and cases of corpus collosotomy, and how this affects a person. Amazing stuff Harry, thank you!!
Article by:
Harry Bickerstaffe
2nd year medical student
Splitting the Brain & Consciousness Sphincter 80:2 December 2016
You are going to the doctor to have your brain cut in half. You probably have epilepsy, very bad epilepsy because you’ re saying goodbye to the 200 million axons of your corpus callosum as a last resort.
The split brain phenomenon drives us to wonder whether an area that has no effect on“ my” consciousness is in fact an area that houses a different consciousness
Now some astonishing and subtle things are going to happen- as your brain and mind are split.
Firstly, your epilepsy will hopefully have improved. Apart from that, you appear to have remarkable‘ social ordinariness’— how disappointing for the researchers hoping to probe you. 1 However, when then asking one young split brain patient 2 what he wanted to be when he grew up: his left brain- where language control lies for most people- verbally responded“ a draftsman” whereas his right brain used his left hand to write out“ racing driver”. Maybe not so normal after all.
The easiest experiments with split brain patients exploit the fact that visual fields are interpreted by the opposite brain hemisphere— remember that nearly all body muscles are controlled by the opposite side of the brain( things get confusing very quickly if we forget that). Showing an image to the right eye means only the left hemisphere will see it, in a split brain patient.
Back to cutting your brain in half!
The diagram above 3 shows a classic experiment: the written explanation is a bit wordy, but worth it. A split brain patient again sees words flash infront of her. Each word is only seen by one side of the brain. Every word is an object. When the left eye, i. e. the right hemisphere, sees the word“ hammer” and the patient is asked what she sees, she says“ nothing”, as the left hemisphere( responsible for speech) really does see nothing. However, when asked to pick up the object that they didn’ t see the word for, the left hand( controlled
Reference 3. Cleverly the word appears for less time than it takes for saccadic eye movement, ensuring only one hemisphere will see the word. In this experiment images are used, words have also been used as understanding individual words is not confined to one hemisphere.
by right hemisphere) will pick up the hammer. To make this trickier the objects are hidden behind a screen. The patient chooses the right object from amongst 20 others. When asked what object they are holding behind the screen the patient’ s talkative left hemisphere cannot say. When the object is brought out from behind the screen and the patient is again asked why she chose this object out of 20 possibilities the answer is confabulated, or simply not known. This is peculiar.
In a different experiment a split brain patient watched a series of picture slides, only seen in the left visual field, so the right hemisphere. At one point a nude photo appeared in the slides, the patient was asked what she saw, she said“ nothing”, but then started to laugh. When asked what was funny she told the researcher she didn’ t know, saying that maybe it was something to do with the machine. 4
What would happen to your sense of“ self” the moment your brain is split?
The apparent liberation of the right brain can be seen when split brain patients draw two different figures at the same time, a task impossible for normal people. In the acute phase after surgery the patients’ left and right hands can be seen engaging in a tug of war over an object or even sabotaging each other’ s work! The left hemisphere( with which you would converse) can explain their operation and their condition, yet the left hemisphere remains naive as to the experiences of the right hemisphere. Years after surgery the left hemisphere may still express frustration when the right hemisphere responds to researcher’ s instructions. 5 To ask the left hemisphere what it is like not to know what the right hemisphere is thinking is rather like asking a normal person what it is like not to know what another person is thinking.
The most startling realisation is that we have every reason to believe the right hemisphere is conscious. In fact it is easier to establish the consciousness of the isolated right hemisphere than most toddlers. In even more dramatic operations patients have had their left hemisphere removed, leaving only their right— we rightly think of them as conscious. Patients with only a right hemisphere can live fruitful lives. 6 How then could the presence of a separate left hemisphere rob the other side of its consciousness?
Back to cutting your brain in half. There are no pain receptors in the brain and hemispherectomies have been performed without loss of consciousness, so we can cut you when you’ re awake, too. What would happen to your sense of“ self” the moment your brain is split? Does your subjectivity collapse into a single hemisphere, or do you disappear and become replaced by two new consciousnesses? You cannot be on both sides of the great divide.
Sphincter magazine | volume 80 issue 2 | Winter 2016 edition