Sarcasm and lie detection failure signals dementia: Study

By Dr. Ananya Mandal, MDApr 17 2011

Researchers have found that inability to recognize others' insincerity, lies and sarcasm could be a warning sign of a form of dementia. They found that people with frontotemporal dementia - a type of dementia that affects the frontal and temporal lobes of the brain - often lose the ability to detect sarcasm and lies, while people who grow older normally don't experience this.

They note that because frontotemporal dementia affects regions of the brain involved in complex, higher-order processes like personality and behavior, patients may show certain striking symptoms like behaving in compulsive, socially inappropriate ways or suddenly changing religions. They also become gullible, as evidenced by the many patients who lose money to hackers and scammers online.

The team from the University of California, San Francisco set out to find the strength of the association between frontotemporal dementia and the failure to identify insincerity or deception. They asked 175 older adults, more than half of whom had some form of dementia, to watch a video of two people speaking. One of the speakers occasionally lied or used sarcasm - made clear by verbal and non-verbal cues. Viewers were then asked a series of yes or no questions about what they saw. Researchers also took MRI scans of the participants' brains.

Those who were mentally healthy had no problem identifying the speaker's lies and sarcasm. But those whose brain scans showed signs of frontotemporal dementia were blind to the deception. People with other types of dementia, including Alzheimer's, performed somewhat better on the lie-detecting task. The study's authors concluded that the inability to perceive lies or sarcasm may help doctors identify patients with dementia, especially since other early behavioral warning signs tend to be overlooked, misdiagnosed as symptoms of depression, mid-life crisis or Alzheimer's.

“We have to find these people early,” said senior author and UCSF neuropsychologist Katherine Rankin, noting that early detection offers the best chance for intervention and treatment. Frontotemporal dementia is rare, making up perhaps 5% of patients with dementia; by comparison, Alzheimer's disease accounts for nearly 80% of such patients. Frontotemporal dementia tends to occur at a younger age than Alzheimer's, typically between the ages of 40 and 70. “If somebody has strange behavior and they stop understanding things like sarcasm and lies, they should see a specialist who can make sure this is not the start of one of these diseases,” said Rankin.

The findings were presented at the annual meeting of the American Academy of Neurology in Hawaii.

Dr. Sam Gandy, associate director of the Mount Sinai Alzheimer's Disease Research Center in New York City, said “neuroanatomy can be surprising.” “Phenomena that sound very complex can sometimes be very discretely localized,” he added. “Language, short-term memory, and recognition of 'self' are examples of clearly complex phenomena that can be dramatically affected by rather small lesions. The fact that Rankin and colleagues were clever enough to formulate the problem properly so that the study could be undertaken is a testament to their skills as outstanding bedside clinical neurologists,” he said.