In a phenomenon less well recognized but still widely known, light stress can

slightly improve performance—say, in examinations—whereas heavy stress causes

dysfunction.

 

But few people know more about really heavy stress than that it can cause

depression. For instance, most people know that an “acute stress depression”

makes thinking dysfunctional because it causes an extreme of pessimism, often

extended in length and usually accompanied by activity- stopping fatigue.

Fortunately, as most people also know, such a depression is one of mankind’s

more reversible ailments. Even before modern drugs were available, many people

afflicted by depression, such as Winston Churchill and Samuel Johnson, gained

great achievement in life.

 

Most people know very little about nondepressive mental breakdowns influenced by

heavy stress. But there is at least one exception, involving the work of Pavlov

when he was in his seventies and eighties. Pavlov had won a Nobel Prize early in

life by using dogs to work out the physiology of digestion. Then he became

world-famous by working out mere-association responses in dogs, initially

salivating dogs—so much so that changes in behavior triggered by

mere-association, like those caused by much modern advertisement, are today

often said to come from “Pavlovian” conditioning.

 

What happened to cause Pavlov’s last work was especially interesting. During the

great Leningrad Flood of the 1920s, Pavlov had many dogs in cages. Their habits