Consciousness: A Very Short Introduction by Susan Blackmore

Consciousness: A Very Short Introduction by Susan Blackmore

Author:Susan Blackmore
Language: eng
Format: epub, pdf
ISBN: 9780192513724
Publisher: OUP Oxford
Published: 2017-07-28T04:00:00+00:00


Splitting brains

What would it be like to have your brain cut in half? This may sound like a thought experiment, but in fact, in the 1950s and 1960s, this drastic operation was performed on people with epilepsy whose life was made unbearable by almost continuous seizures. Today they can be treated with drugs or less invasive surgery, but then the only option was to separate the two halves of the brain, so preventing the seizures spreading from one side to the other. In most of these patients the main connection between the two hemispheres, the corpus callosum, was severed, leaving the brain stem and some other connections intact. So it is an exaggeration to say that their brains were cut in half, but without the corpus callosum most of the usual traffic between right and left hemisphere stops.

What happened? Remarkably, very little happened; the patients recovered well and seemed to live a normal life, with little or no change in personality, IQ, or verbal ability. But in the early 1960s, psychologists Roger Sperry and Michael Gazzaniga performed experiments that revealed some extraordinary effects.

The experimental design depends on knowing how the sense organs are connected to the brain. Information from the right ear goes to the right hemisphere (and left to left), but in vision information from the left side of the visual field goes to the right hemisphere (and vice versa), as in Figure 15. This means that if you look straight ahead, everything seen to the left goes to the right hemisphere and everything on the right goes to the left hemisphere. Things are also crossed over for the body, with the left half of the body controlled by the right hemisphere (and vice versa). Normally the two hemispheres are connected, so that information quickly gets through to both halves, but in a split-brain patient they are not. Knowing this, the experimenters could communicate separately with each of the two hemispheres of the one person. Would the two halves behave like two separate people? Was each independently conscious?

15. The diagram shows how visual information is sent from one visual field to the opposite side of the brain, crossing over in the optic chiasm. Split brain patient PS was shown a snow scene to the left and a chicken claw to the right, but the speaking left hemisphere could see only the chicken claw.



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