BERLIN: Problem drinkers may know how to have a laugh but they often do not know how to take a joke or understand a punchline, researchers in Germany found in a study released Wednesday.

A study of 29 recovering alcoholic patients in a clinic in the western German city of Bochum were tested to measure their mood, intellectual ability, memory and psychomotor skills and capacity to appreciate jokes.

The results were matched against those of 29 healthy controls.

In the humor test, subjects were given a choice of punchlines for jokes, some of which were more coherent and logical than others.

The following is one of the jokes used on the subjects.

It was Mother's Day. Anna and her brother had told their mother to stay in bed that morning. She read her book and looked forward to breakfast. After a long wait she finally went downstairs. Anna and her brother were both eating at the table.

Alternative endings:
a) Anna said: "Hi mom, we didn't expect you to be awake so early."
b) Anna picked up an egg and smashed it on her brother's head.
c) Her brother said: "We have a new teacher at our school."
d) Anna said: "It's a surprise for Mother's Day. We cooked our own breakfast."

The researchers found a marked difference between the two groups with less than 68 percent of the alcoholics able to pick the right punchline, d, versus 92 percent in the healthy control group.

The groups were also tested for aptitude at predicting and understanding other people's behavior, known as "mentalizing ability".

"Alcoholics also fared less well in the working memory tests and mentalizing ability tests, prompting speculation that deficits in these areas can impact upon a problem drinker's capacity to understand jokes and find them funny," the study said.

The authors from the Ruhr University in Bochum said in a synopsis of the study for the journal Addiction that an inability to understand others' mental states and a lack of humor can affect social skills and interpersonal relationships.

This, in turn, can impair rehabilitation and recovery.

The authors called for special treatment of alcoholics to take these deficits into account.