When most people think about the telltale signs of dementia, memory loss is often top of mind. But while it's true that trouble with short term memory is a hallmark of Alzheimer's disease—the most common form of dementia—other categories of chronic cognitive impairment (e.g. Lewy Body dementia, vascular dementia, etc.) have different symptoms.

In fact, a new study from the University of California, San Francisco, (UCSF) Department of Neurology recently revealed an intriguing link between delinquent actions and certain types of dementia.

It's no secret that out-of-character behavior is one of the primary indicators of dementia. But a recent analysis of nearly 2,400 dementia patients revealed that criminal acts such as theft, trespassing, public urination and sexual advances were more common among individuals who are in the initial stages of the behavioral variant form of frontotemporal dementia (FTD).

People with FTD tend to experience the first symptoms of their condition earlier than those with Alzheimer's. In fact, about 60 percent of people with FTD are between the ages of 45 and 64, according to the National Institutes of Health (NIH), making it about as prevalent as Alzheimer's among people under 65.

As its name suggests, FTD is a degenerative disease that affects the frontal and temporal lobes of the brain.

The frontal lobes govern the brain's executive functioning capabilities—planning, multitasking, recognizing mistakes and prioritizing tasks. It also acts as an important filter, helping us distinguish between the appropriate and inappropriate ways to behave in a given situation. People with damage to their frontal lobes may experience issues with things like managing finances or loudly laughing during a solemn event.

The temporal lobes bear much of the responsibility for governing emotions and language processing, as well as connecting particular memories with certain senses (e.g. the song that was playing during your first kiss). People with damage to their temporal lobes can have trouble recognizing dangerous situations, or making sense of and responding appropriately to emotional situations.

Understanding that FTD can cause dramatic behavioral changes in adults is key to the early detection of the disease, not to mention that appropriate handling of outwardly "criminal" acts committed by those with FTD.

"Judicial evaluations of criminality in the demented individual might require different criteria that the classic ‘insanity defense,' used in the American legal system;" the authors of the UCSF study write. Their findings highlight a question that will only increase in importance as the number of adults with dementia rises: Is it appropriate to punish a person for a crime they don't even understand they've committed?

On a more individual level, the knowledge that uncharacteristic criminal behavior can accompany the onset of FTD is be beneficial for families who are perplexed by their aging loved one's peculiar (and sometimes disturbing) actions. An adult who suddenly engages in criminal or wildly inappropriate acts should be evaluated for dementia, the study authors advise.