六级阅读考前补习（3）
Test Three
1
A well?stablished distinction in memory theory is that between short?erm and long?erm memory. The former refers to our ability to do such things as remember telephone numbers long enough to dial them; the latter―concerns the wide range of ways in which experiences can affect behavior many years later. Given the two different kinds of ability, it is reasonable to hypothesize that each is represented differently in the brain. An experiment was designed to test the hypothesis that long?erm memory implies a chemical change in the brain cells while short?erm memory involves patterns of impulses in circuits of nerve cells.?
One group of rats were taught to run through a maze. Five minutes after learning the task, they were cooled to 5℃, the temperature at which all electrical activity in the brain ceases. They were then kept at this temperature for 15 minutes before being allowed to return to their normal temperature. They were then run through the maze, again.?
A second group of rats were taught to run the same maze, and then immediately cooled to 5℃ for 15 minutes. After being allowed to return to their normal temperature, an attempt was made to run the second group through the maze again. It was found that rats in the first group had no difficulty with the maze the second time, suggesting that they did not have to relearn the task. Rats in the second group which was cooled immediately after learning the maze, on the other hand, could not negotiate the maze successfully, i.e., they apparently could not remember what they had learned.?
It was concluded from this experiment that short?erm memory (in rats, at least ) is unlike long?erm memory. Short?erm memory involves electrical impulses since at a temperature where electrical activity ceases, there is no memory. Long?erm memory, in contrast, is unaffected by the disruption of electrical activity and may involve structural changes in brain cells.
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