Ever since boxing's bareknuckle days, the punch-drunk fighter has been a fixture of the sport.
The victim of too many blows to the head, a retired boxer in his 40s might resemble an old man in decline: He moved slowly, had trouble rising from his chair or turning over in bed. He couldn't pronounce words or nimbly write his name. He tended to forget things. Sometimes his hands shook.
Not until the 1960s did doctors begin to realize that these boxers suffered from a disorder of the brain known as Parkinson's syndrome. It can be caused by any type of serious head trauma, as well as encephalitis, carbon monoxide poisoning and certain medications.
In boxing, fighters who suffer repeated knockouts are its most frequent victims. But sometimes, talented boxers who endure many rights and lefts to the head also suffer. Boxers such as Muhammad Ali.
"When a boxer gets hit, the reaction is to turn his head to the other side," said Dr. Hamilton Moses, a neurologist at Johns Hopkins Hospital. "This produces a rotational injury" -- damaging certain nerve cells in the brain's midsection that are responsible for making movement fluid, easy and natural.
The boxer's syndrome is similar but not identical to Parkinson's disease, a more common affliction that afflicts one person (usually elderly) in 200.
The disease, said Moses, almost always gets progressively worse, although medication can slow the slide considerably. The syndrome often stabilizes after initially getting worse. But, when it doesn't, it's harder to control with drugs.
Fighters with the boxer's syndrome are less likely to develop hand tremors, but the tremors tend to be more disabling when they do occur. People with the syndrome are much more likely to lose memory and intellect -- half have this trouble, compared with 20 percent of patients with Parkinson's disease.
But, often, an ex-fighter with a sharp mind can appear stupid simply because he can't express himself. That's his speech impairment, brought on by brain damage.
"All this," Moses said, "is the rationale why the neurological community has taken the strong position that boxing should be outlawed."