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Sense of humor an early casualty of Alzheimer's disease

Subtle -- and not-so-subtle -- shifts in a person's sense of humor can be a sign of Alzheimer's disease, and may start to emerge years before other symptoms, a new study suggests.

Laughing at "frankly inappropriate" moments, taking jokes literally or missing the point, and preferring childish or slapstick humor are some of the behaviors highlighted in the study, published in the Journal of Alzheimer's Disease.

Researchers in London collected data on 48 patients with Alzheimer's or other types of dementia, including frontotemporal lobar degenerations (FTLD) and semantic dementia (SD), who were being treated at a cognitive disorders clinic, along with 21 healthy people for comparison. They conducted neuropsychological exams to assess the patients' cognitive function, along with brain scans and other testing.

A relative, friend or caregiver who had known the person well for at least 15 years was asked to fill out a questionnaire about their sense of humor and how it had changed over the years. They were asked to rank how much the person liked different types of comedy, both 15 years ago and currently. The study grouped comedy styles into three broad categories: farcical or slapstick (like the character Mr. Bean); absurdist (like Monty Python); and satirical.

The questionnaire also asked whether the patient ever laughed at things other people didn't find funny.

The study found dementia patients were significantly less likely than the healthy group to enjoy satirical or absurdist humor, and more likely to retain an enjoyment of slapstick. The patients' liking of satirical or absurdist humor was found to decline an average of about nine years before typical dementia symptoms set in.

Many patients also developed a distinctive habit of laughing at "dark" or inappropriate things, the researchers said. Comments made by the patients' caregivers highlight some of the troubling changes they observed:

"Rarely laughs at jokes now except own, often inappropriately. Jokes taken literally, misses the point."

"Used to be very witty but that has all gone; humour has to be more obvious, laughs if others laugh."

"Has developed a dark and misplaced sense of humour; relishes other people's mishaps or upset."

"Early on laughed very loudly at things that were only mildly funny, flippant or 'over the top'; now laughs all the time at things that are not particularly funny and will say 'I'm laughing and I'm not sure why I'm laughing.' When I badly scalded myself the other year, thought it was hilarious."

"Tends not to laugh as much at things previously thought funny ... sometimes laughs inappropriately at news items."

The researchers note their findings were limited by the fact that the study involved only a small number of people and relied on caregivers' and control subjects' recollections from 15 years ago, which may be subject to recall bias. They say more work is needed to understand "humor behavior and its potential as a disease biomarker," perhaps by studying people over a longer period of time before dementia cases develop.

They also suggest that a better understanding what dementia does to a person's sense of humor could help improve social functioning and quality of life for patients and their caregivers. "We hope that our findings will stimulate interest in humor as an engaging, ecologically relevant and informative index of social functioning in neurodegenerative disease," they write.