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Sleep Now, Remember Later
How sleep helps US consolidate memories is still largely a mystery. A recent study from the University of Liibeck, in Germany, offers one clue-Subjects were given a list of 46 word pairs to memorize, just before sleep. Then when they reached the deepest stages of sleep, electrical currents were sent through electrodes on their" heads to induce very slow brain waves. Such slow waves were induced at random in the brains of one group of subjects, but not another.
The next morning, the slow-wave group had better recall of the words. Other types of memory were no| improved, and inducing the slow waves later in the night did not have the same eftect. Why and how the slow waves improved memory is not yet understood, but they are thought to alter the strengths of chemical connections, or synapses, between specific pairs of nerve cells in the brain. Memories are "stored" in these synapses: changing the strength of the synapses increases the strength of the memories they store.
It’s not just memory that is improved by sleep. Recent studies indicate that sleep riot only helps store facts, it also helps make connections between them. Ullrich Wagner arid colleagues in Germany used a puzzle in which players were given a string of numbers, and required to make a series of seven calculations based on these numbers. The seventh calculation (which depended on the preceding six) was the" answer. "Participants repeatedly played the same game with the same roles, but different sets of numbers.
The researchers structured the game such that the second calculation always gave the same answer as the seventh calculation-the final answer. If players recognized this rule, they could get to the final answer much faster. Sonic of the players played the game in the morning, then did other things for eight hours or so, then played the game again. Others played the game first in the evening, then slept, then played it again alter awakening. The players who slept were almost three times more likely to have the insight that allowed them to spot the rule.
Why is this important Some sleep researchers believe that for every two hours we spend awake, the brain needs an hour of sleep to figure out what all these experiences mean, and that sleep plays a crucial role in constructing the meaning our lives come to hold. Breakdowns in such sleep-dependent processing may contribute to the development of depression, and may explain why some people who experience horrific traumas go on to develop post-traumatic stress disorder.
Apart from helping store facts, sleep also