1964 was the year when the left-brained '50s really turned into the right-brained '60s. Frank Sinatra and Doris Day were still dominating the charts, but a group of Liverpool boys showed they could write their own tunes with A Hard Day's Night. Yes, the times they are a-changing, as Robert Zimmerman sang, but under the more right-brained name of Bob Dylan.
In sync with the times, Roger Sperry devised a pioneering study that teaches us a lot about the structure of the brain. In fact, Sperry ended up getting a Nobel Prize for his research into the brain and his technique of "hemispheric disconnection" - opening up the skull of living patients and severing the nerve fibres that hold the two hemispheres of the brain together. Sperry was interested in "unity of consciousness" - with two brains inside their heads, did the split-brain patients now have one mind or two?
This is a natural experiment because Sperry used patients who had already had the split-brain operation for medical reasons. If it had been a lab experiment, Sperry would have to have taken perfectly healthy people and subjected half of them to the split-brain op just to see what would happen - very unethical!
Mark Holah's website contains an excellent summary of the study, multiple choices quizzes and more
Gary Sturt's website also contains a quick sumary of the study
The Nobel Prize website has an interactive game to get your head around split-brains
This news article on Splitting the Brain from the 1970s sums up the research well
Neuroscience For Kids has lots of illustrations of the study and links it to handedness
Scientists have known for a long time that the brain is made up of two mirror-image halves, called hemispheres. The 19th century scientist and philosopher Gustav Fechner suggested that, if the two hemispheres were separated, a person would then have two minds! It was only in the 20th entury that medical technology reached a level where ideas like this could be tested. Some of the most important resarch was carried out by Roger Sperry, at first on animals like cats and monkeys.
This resarch showed how the body and the brain are "cross-wired", with the left hemisphere controlling and receiving input from the right side of the body and the right hemisphere controlling and receiving input from the left side of the body.
A practical use for this sort of brain surgery was the treatment of epilepsy. Epilepsy is a disorder that makes sufferers undergo fits or seizures - ranging from mild trances to violent convulsions that can be life-threatening. Brain-scanning technology (see Dement & Kleitman and Maguire et al.) shows a build-up in electrical activity across the two hemispheres just before a seizure. A new operation - called a commissurotomy - severed the bridge of nerve fibres connecting the two hemispheres and reduced the danger of epileptic attacks. When animals had this bridge (called the CORPUS CALLOSUM) cut they experienced terrible side effects but humans seemed to function quite normally, with only minor problems with memory and long-term planning. Sperry was now in a position to test people who had had their brains "split" to see if they possessed one mind or two.
Sperry used a group of 11 patients who had all had commissurotomies as a treament for severe epilepsy. As part of a natural experiment, he compared them to 11 healthy persons at a variety of tasks.
Sperry designed an apparatus for his tests. This used a projector to flash words or images onto a screen in the subject's left or right field of vision (LVF or RVF). The words or images would appear for just 1/10th of a second, since this was long enough to be noticed but not long enough for the other eye to focus too. This ensured that the information that was flashed up only went to one hemisphere (to the left if flashed in the RVF, to the right if flashed in the LVF).
The apparatus also had a covering screen under which the subjects would place their hands to investigate objects on a tray. Again, it was important they could not see the objects, only touch them, so that the information would go to just one hemisphere (to the left if handled by the right hand, to the right if handled by the left hand).
If words or images were flashed in the LVF (input to right hemisphere), the subject claimed he did not see anything.
If asked to use his left hand (controlled by right hemisphere) to point to the object in a collection of objects, the hand would find the object the patient had insisted he didn't see.
The right hemisphere can understand language, but cannot speak or write. Any spoken or written answers the patient gave were coming from the left hemisphere.
Different signs to different hemispheres: a $ sign was flashed to LVF and ? sign to RVF; the patient was asked to draw the sign with his left hand then say out loud what sign he had seen.
Composite words: The word "keycase" was projected, but "key" was flashed to LVF and "case" to RVF; the subject was asked to select the thing seen from a bag of objects with the left hand, write the thing seen with the right hand then say the thing seen out loud.
Touching objects: objects were placed in the subject's hands, right or left, and they were asked to say them out loud or write them; objects were then put in a grab bag and patients had to reach inside and find the object they had touched before.
Dual processing: objects were placed simultaneously in each hand then hidden among a pile of items; subjects were asked to use both hands to search for the original objects.
In everyday life the patients had very few problems because they could use both eyes or both hands and say information out loud so it was shared by both hemispheres.
The patients appear to have two independent streams of consciousness, each with its own separate memories, perceptions and impulses to act.
Sperry carried out further research into the "silent" right hemisphere and found that it was dominant with respect to some abilities, like spatial awareness (see Maguire et al.) and emotion.
Other researchers have found different results, because individuals vary so much. Some patients show ipsilateral control, with their right hemisphere controlling the right side of the body rather than the usual cross-wiring. Other patients show more language ability in the right hemisphere - this is sometimes true of left-handed people.