05/11/2005
Mixed Messages
There are two sides to every question. This often quoted refrain came to mind recently when I saw a picture of a two-headed turtle. I’ve forgotten where I saw the photo but believe it was of a turtle that was born in the UK last year. The accompanying news item said that the two heads operated independently but that the right one was dominant. Sometimes the left head would be nibbling away at some delicacy and the right head would see a tasty tidbit elsewhere. Being dominant, the right head would move the body of the turtle towards the new food source, leaving the other head nibbling on nothing. There are certainly two sides to this creature!
I suppose that the closest human analogy would be conjoined Siamese twins who have to resolve differences amicably throughout their lives. Thanks to modern medicine and remarkably skilled surgeons, a much more pleasant outcome is possible. I read recently that those twins conjoined at the head are doing well after their separation in a succession of operations at a hospital in New York last year.
In the two-headed turtle, two separate brains in two separate heads control the actions of a single body. We only have one brain, but could it be that in that one brain we have two separate minds? This possibility is the subject of an article, “Of Two Minds”, by Jim Holt in last Sunday’s April 8 New York Times Magazine section. After reading the article I decided I needed to know a bit more about the brain’s structure so it was off to my 1962 World Book Encyclopedia. (I figured that the anatomy of the brain hasn’t changed much since 1962, even though our understanding has grown immensely.)
Let’s concentrate on the cerebrum, which makes up about 85 percent of the brain’s weight and is the seat of our intelligence. The cerebrum is divided into two halves, sort of like a shelled walnut. These two halves of the cerebrum are connected by the corpus callosum, a bundle of nerve fibers that serves as the communications link. Another important feature is the cerebral cortex, a carpet of nerve cells covering the cerebrum. The cerebral cortex contains the so-called sensorimotor regions that send the signals to arms, legs, facial muscles, etc. to do their thing. Incoming sensory messages such as taste, touch, muscle movement etc. also come into the cerebral cortex.
An important feature is that these incoming and outgoing messages cross over in the brain stem and spinal cord. This is why the right hemisphere controls movements of the left side of the body and the left hemisphere controls movements on the right side. Typically, the left half of the cerebrum is the dominant half, accounting for the fact that the majority of people are right-handed. With two halves of the cerebrum operating on different parts of the body, it seems rather important that one half knows what the other half has in mind. Simply clapping one’s hands at the end of a stirring musical performance requires that the two halves send the proper messages to the respective arms and hands. Otherwise, the clapping hands might miss each other entiely!
Normally, the two halves are in touch with each other through the corpus callosum and any disputes are settled amicably without our even being aware of the disagreement. However, the Times article cites examples in which patients suffering from severe cases of epilepsy were subjected to operations in which the corpus colossum was severed, cutting off the communication between the two halves of the brain. This operation, no longer in vogue, was thought to avoid the spread of the epileptic seizures from one side of the brain to the other.
Patients having this operation generally seemed normal but under certain conditions were quite abnormal. For example, one patient was shown the word “hat” on a screen limited to the patient’s left half of his visual field. When his left hand picked the hat out of a group of different objects, he maintained that he hadn’t seen the word. The same patient, when shown a picture of a nude woman in just one half of his visual field, would smile or even blush but at the same time wasn’t able to identify what it was that caused his reaction. The two halves of the brain weren’t communicating without the connecting nerve fibers.
Under normal circumstances, with the visual experience not restricted to just half the normal visual field, the patient was normal. One half of the cerebrum takes over and the other stays quiet; everything seems normal. However, the experiments on these “split-brain” patients raised the question as to whether we may indeed have two minds in our one brain, with the corpus callosum acting as the critical link.
What if we could read the mind? Magicians do it all the time but we know they use tricks to accomplish the feat. The Times article also mentioned work published in the May issue of Nature Neuroscience in which a form of MRI, magnetic resonance imaging, was used to read minds. Well, it was at least a step in that direction. I visited the Scientific American and the World Science Web sites to flesh out the details of these mind reading experiments. There were two studies that were reported.
Yukiyasu Kamitani of ATR Computational Neuroscience Laboratories in Japan collaborated with Frank Tong at Princeton (he’s now at Vanderbilt University) in experiments in which patterns of stripes oriented in different directions were shown to the subjects. There were 8 different patterns of stripes. MRI brain scans were made while the subjects gazed at a particular pattern. There were slight differences in the brain scan patterns as the subjects gazed at the different stripe patterns. A computer program was written that could detect and tell the differences among the patterns. Using the program and MRI brain scans, the researchers correctly identified which patterns the subjects were looking at.
The real mind reading came about when the researchers showed the subject a “plaid” pattern consisting of two sets of stripes simultaneously. The subject was told to ignore one of the patterns and concentrate on the other. Sure enough, the researchers could correctly identify that pattern from the brain scans. Basic mind reading 101!
The other work was performed by John-Dylan Haynes and Geraint Rees at University College London. They used the same MRI brain scan approach, but with a twist. They showed the subjects two images in succession. However, the first image was flashed by so quickly that the subjects could only remember the second one. Yet the MRI brain scan correctly identified the first image even though the subject could not. This experiment must tell us something about how fast our brain can detect something and how slow it is in processing that information to our consciousness.
On reading of this experiment, the thought occurred to me that the advertisers who dream up commercials on TV may have beaten these researchers to the punch. As I recall, some years ago there was a fuss about flashing fleeting “subliminal” images or messages within commercials. The idea was that the viewer would subconsciously remember the images or messages and be stimulated to buy the product. I assume that, to be successful, the subliminal image would have to be considered by the brain to be worth storing in memory long enough to prod me to buy the product. Actually, it’s a bit frightening to think my brain would take such action without me taking part in the decision.
Allen F. Bortrum
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