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All types of stress study，whether under laboratory or real-life situations，study mechanisms for increasing the arousal level of the brain.
The brain blood flow studies show that reciting the days of the week and months of the year increases blood flow in appropriate areas，whereas problem solving which demands intense concentration of a reasoning type produces much larger changes in the distribution of blood in the brain.
Between these basic studies of brain function and real life situations there is still a considerable gap，but reasonable deduction seems possible to try and understand what happens to the brain.Life consists of a series of events which may be related to work or to our so-called leisure time.Work may be relatively automatic——as with typing，for instance，it requires intense concentration and repetition during the learning phase to establish a pat tem in the brain.Then the typist’s fingers automatically move to hit the appropriate keys as she reads the words on the copy.
However，when she gets fired she makes mistakes much more frequently.To overcome this she has to raise her level of arousal and concentration but beyond a certain point the automatic is lost and thinking about hitting the keys leads to more mistakes.
Other jobs involve intense concentration such as holding bottles of wine up to a strong light and turning them upside down to look for particles of dirt falling down.This sounds quite easy but experience teaches that workers can do this for only about thirty minutes before they start making a mistake.This is partly because the number of occasions with dirt in the bottle is low and the arousal level，therefore，fails.Scientists have shown that devices to raise arousal level will increase the accuracy of looking for relatively rate events.A recent study of the effect of less of sleep in young doctors showed that in tests involving a challenge to their medical judgment when short of sleep they raised their arousal level and became better at tests of grammatical reasoning as well.