Many a myth has grown up around the brain's asymmetry(不对称现象). 71. {{U}}The left cerebral hemisphere is supposed to be the coldly logical, verbal and dominant half of the brain, while the right developed a reputation as the imaginative side, emotional, spatially aware but suppressed. Two personalities in one head. Yin and Yang, hero and villain.{{/U}}
To most neuroscientists, of course, these notions are seen as simplistic at best and nonsense at worst. So there was general satisfaction when a couple of years ago, a simple brain scanner test appeared to reveal the true story about one of neurology's greatest puzzles: Exactly what is the difference between the two sides of the human brain? Some clinical neurologists had been pursuing the idea that the difference between the two hemispheres lay in their style of working.
The left-brain, they reckoned, focused on detail. This would make it the natural home for all those mental skills that need us to act in a series of discrete steps or fix on a particular fragment of what we perceive--skills such as recognizing a friend's face in a crowd or "lining up" words to make a sentence.
By contrast, the right brain concentrated on the broad, background picture. The researchers believed it had a panoramic focus that made it good at seeing general connections; this hemisphere was best able to represent metaphorical aspects of speech.
For example, in a test in which split-brain patients had to match a series of household objects, the left brain would match by function while the right would match by appearance. So, when seeing a cake on a plate, the left brain would connect to a picture of a fork and spoon while the right brain would select a picture of a broad-brimmed hat. 72. {{U}}This evidence appeared to support the idea of a highly modular brain in which, for example, thinking in logical categories was a strictly left hemisphere function while mental imagery and spatial awareness were handled on the right.{{/U}}
But this picture changed dramatically as soon as brain-scanning experiments began to show that both sides of the brain played an active role in such processes. 73. {{U}}Rather it seemed to be the processing styles that distinguished the two halves--under the scanner, language turned out to be represented on both sides of the brain in matching areas of the cortex (皮质). Areas on the left dealt with the core aspects of speech such as grammar and word production while aspects such as intonation and emphasis lit up the right side.{{/U}} In the same way, the right brain proved to be good at working with a general sense of space, while equivalent areas in the left-brain fired when someone thought about objects as particular locations.