Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: Eduardo Cervantes on 27/06/2010 14:30:02
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Eduardo Cervantes asked the Naked Scientists:
If your brain was cut in two, could you read two books at the same time and understand them? Would you be in effect, two people?
What do you think?
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Each half doesn't get the full picture ...
The optic nerves from both eyes meet and cross at the optic chiasm, at the base of the hypothalamus of the brain. At this point the information coming from both eyes is combined and then splits according to the visual field. The corresponding halves of the field of view (right and left) are sent to the left and right halves of the brain, respectively, to be processed. That is, the right side of primary visual cortex deals with the left half of the field of view from both eyes, and similarly for the left brain.] A small region in the center of the field of view is processed redundantly by both halves of the brain.
http://en.wikipedia.org/wiki/Visual_system
e.g. ...
Hemispatial neglect results most commonly from brain injury to the right cerebral hemisphere, causing visual neglect of the left-hand side of space ... For example, a stroke affecting the right parietal lobe of the brain can lead to neglect for the left side of the visual field, causing a patient with neglect to behave as if the left side of sensory space is nonexistent; although they can still turn left. In an extreme case, a patient with neglect might fail to eat the food on the left half of their plate, even though they complain of being hungry. If someone with neglect is asked to draw a clock, their drawing might show only the numbers 12 and 1 to 6, the other side being distorted or left blank. Neglect patients may also ignore the contralesional side of their body, shaving or adding make-up only to the non-neglected side.
http://en.wikipedia.org/wiki/Hemineglect
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Actually, RD, it's more subtle than that; if you assume that by "split brain" the patient has a divided corpus callosum, divorcing the right and left hemispheres but leaving the optic chiasm intact (so the visual pathways are unaffected), anything viewed on the right hand side of the body is presented to the left hemisphere and vice versa. Patients with this very presentation were investigated by Nobel prizewinner Roger Sperry in the 1960s, revealing some extraordinary aspects of brain function.
For instance, such a patient sat in front of a screen onto which objects or words can be flashed up will identify by name an object flashed on the right side, but cannot do so for an object flashed on the left; asked to find something that would "go with" the object whose name was flashed up and they'll retrieve say a teapot to accompany the "cup" word shown on the screen.
But ask them "what did you see" and the answer will be "nothing" - because the left brain, where spoken language resides, did not see a word; hence the right hemisphere is functioning independently of the left and appears to have at least limited ability to read words and comprehend their meaning.
Therefore, theoretically, it might be possible to present simultaneously two books to someone with this split-brain preparation, and they could read them book at the same time. But only the one viewed by the left brain would be able to discuss anything about the story; even more fun would be to swap the books round later - then each brain could enjoy a new story that it hadn't witnessed before!
Chris