We sometimes think humans are uniquely
vulnerable to anxiety, but stress seems to affect the immune defenses of lower
animals too. In one experiment, for example, behavioral immunologist Mark
Laudenslager, at the University of Denver, gave mild electric shocks to 24 rats.
Half the animals could switch off the current by turning a wheel in their
enclosure, while the other half could not. The rats in the two groups were
paired so that each time one rat turned the wheel it protected both itself and
its helpless partner from the shock. Laudenslager found that the immune response
was depressed below normal in the helpless rats but not in those that could turn
off the electricity. What he has demonstrated, he believes, is that lack of
control over an event, not the experience itself, is what weakens the immune
system. Other A. was strengthened B. was not affected C. was altered D. was weakened
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