In many ways our sense of humor defines us; it’s the glue that builds friendships and unites entire groups of people. Oftentimes, it’s also used as a vehicle to spread information the public would otherwise find uninteresting (think Comedy Central’s The Daily Show), or to jump start conversations about controversial topics (George Carlin style). That said, we can all identify with the senses of humor in those close to us, but what about when that humor drastically changes? According to a new study, it could be an early sign of dementia.

While dementia and Alzheimer’s disease are often characterized by progressively severe memory loss, these aren’t often the first symptoms of the disease, which affects one in nine older Americans. Rather, studies have shown more subtle symptoms begin to emerge far earlier in a person’s life — signs like an altered walking speed, a declining sense of smell, and beta-amyloid plaques in the eyes (the same ones linked to dementia in the brain) have all been deemed potential early signs of the neurodegenerative disease. Friends and family of dementia patients have also reported changes in behavior; some even saying it was like they were a different person.

So it makes sense that a changed sense of humor could also be an early symptom. According to researchers from University College London, people who specifically developed behavioral variant frontotemporal dementia (bvFTD) — characterized by changes in behavior — exhibited signs of an altered sense of humor at least nine years before more typical signs of dementia emerged. Their senses of humor began to favor slapstick comedy (like Mr. Bean), tragic events (such as natural disasters), and other scenarios that people would not usually find funny, like a barking dog or badly parked car. At the same time, many of these patients also lost interest in higher-level forms of comedy, such as satire and and absurdist humor (like Monty Python).

The researchers discovered these changes by handing out questionnaires to 48 FTD patients’ friends or relatives — all people who’d known them well before their diagnosis. The questionnaires asked about patients’ liking for comedy both at the moment and 15 years earlier; how much exposure to comedy they got from print and media; and how their comedic preferences had changed over time. In all, patients with bvFTD showed the most significant changes in humor when compared to healthy participants or those with other forms of dementia like Alzheimer’s disease.

“As well as providing clues to underlying brain changes, subtle differences in what we find funny could help differentiate between the different diseases that cause dementia,” lead researcher Dr. Camilla Clark said in a press release. “Humor could be a particularly sensitive way of detecting dementia because it puts demands on so many different aspects of brain function, such as puzzle solving, emotion and social awareness.”

It’s worth noting that a lot of “humor is heavily influenced by social and cultural context,” so appreciating it would require understanding these factors, the researchers wrote. So in a way, losing one’s sense of humor is a more subtle form of memory loss. However, to understand the extent to which changes in humor predict the development of bvFTD and other forms of dementia, more research will be necessary.

Source: Clark C, Nicholas J, Gordon E, et al. Altered Sense of Humor in Dementia. Journal of Alzheimer’s Disease. 2015.