Ernest Hemingway underwent 20 gruelling rounds of electroconvulsive therapy （ECT) to cure

Ernest Hemingway underwent 20 gruelling rounds of electroconvulsive therapy (ECT) to cure him of his depression. Having lost many of his memories as a result, he said, "It was a brilliant cure but we lost the patient," and took a shotgun to his head not long afterwards. Ever since ECT was pioneered by Ugo Cerletti, an Italian neurosurgeon, in the late 1930s, it bas had a bad press. In books (The Bell Jar, Zen and the Art of MIotorcycle Maintenance), in song (Electric Co by U2) and in film (One Flew Over the Cuckoo's Nest and Tar-nation), it has been portrayed as a sinister procedure that leaves the patient a dribbling dullard. But in spite of this, ECT remains one of the fastest-acting and most effective antidepressant treatments known.

Why it should be so effective, though, is an enigma. On the face of it, running a current of almost an amp through someone's brain seems a silly thing to do. But a study by Johan Hellsten of Lund University in Sweden bas cast some light on the question. Dr. Hellsten has shown that ECT leads to the gene ration of new blood vessels [n part of the brain implicated in depression.

Previous brain imaging studies have shown that patients with long-term depression have a smaller hippocampus (part of the brain that deals with emotion and memory) than average. But, while it is possible to use scanners to look at brain volume in people, it is impossible to examine what is going on at a cellular level. For this reason, Dr. Hellsten used rats.

There were two groups of rats in his experiment. The test group received ECT once a day. for ten days while the control group received a sham treatment. On the eleventh day! the rats were killed and examined. Dr. Hellsten found a 20 fold increase in the number of endothelial cells (the cells that line blood vessels) in the hippocampuses of the test rats, compared with the control rats. He also found a 16% increase in the total length of the blood vessels in their hippocampuses. If the blood vessels of any organ--including the hippocampus are reduced, that organ begins to atrophy. ECT appears to reverse this atrophy. This study is the first to show an increase in blood-vessel production in connection with an anti-depressive treatment.

Why ECT has this effect is still a subject of speculation, but Dr. Hellsten suspects that what is happening is a consequence of the brain trying to protect itself. ECT works by creating an artificial epileptic seizure. Natural seizures, which often last much longer than the 30 seconds or so employed for ECT. result in the production of chemicals called growth factors that stimulate cell division and growth. This response helps to compensate for the damage that a seizure can do. Though modern ECT does not last long enough to cause damage, it nevertheless provokes the damage-limitation response.

ECT, invented in a more brutal age, was originally seen as a way to control unruly patients, often against their will. Ironically, it now serves to give will back to those who have lost it.

The word "gruelling" in the first paragraph probably means ______.

A．intermittent.

B．incessant.

C．toilsome.

D．numerous.