Lesson12 Short-term and Long-term Memory
A well-established distinction in memory theory is that between short-term and long-term 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-term memory implies a chemical change in the brain cells while short-term memory involves patterns of impulses in circuits of nerve cells.
One group of rats was taught to run through a maze. Five minutes after learning the task, they were cooled to 50C., 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 50℃. 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 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-term memory is unlike long-term memory. Short-term memory involves electrical impulses since at a temperature where electrical activity ceases, there is no memory. Long-term memory, in contrast, is unaffected by the disruption of electrical activity and may involve structural changes in brain cells.
短时和长时记忆
记忆理论中一个得到公认的区别是短时记忆和长时记忆之间的区别。短时记忆指的是我们能记住电话号以便拨打所需的能力，长时记忆涉及到曾经拥有的经历在几年后仍能影响行为的诸多方式。既然存在着这两种不同的能力，假定它们在大脑里有着不同的表现方式就是理所当然的了。科学家们认为长时记忆牵涉到脑细胞的化学变化，而短时记忆涉及到神经细胞里线路的脉冲方式，他们设计了一个试验来验证这个假设。
科学家们教会了一组老鼠如何走迷宫。学会后五分钟，它们被冷却到了五摄氏度，在这一温度，大脑里所有的电活动都会停止。保持在这一温度十五分钟之后，它们恢复到正常的体温。然后，它们被再次放入到了迷宫中。
第二组老鼠学会如何走同样的这个迷宫之后，马上就被冷却到五摄氏度并保持十五分钟。在恢复到正常体温后，科学家们试图让第二组老鼠再次走迷宫。结果发现第一组老鼠在第二次很轻松地就走出了迷宫，说明它们不必重新学习这项任务。然而，学会走迷宫之后马上就被冷却的第二组老鼠却不能成功地走出迷宫，也就是说，它们明显记不起已经学会的东西了。
这个实验的结论是，短时记忆和长时记忆是有区别的。短时记忆涉及到电脉冲，因为在电活动停止的温度条件下，记忆就不存在了。相比之下，长时记忆不会受到电活动中断的影响，可能会涉及脑细胞的结构改变。 |