A new study carried out by researchers at the University of California, San Francisco, shows that losing the ability to identify sarcasm and lies is an early indication of frontotemporal dementia. While doctors have long recognized that people with this form of dementia lose the capacity to recognize insincerity—they are often easy prey for con artists and scams, for instance—this is the first study to show that a lack of this ability correlates to early changes in the brain.

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Lies And The Aging Brain

Participants in the study viewed videos of two actors talking with each other. One of the actors frequently lied or used sarcasm in ways that were obvious based on context and nonverbal cues. After watching the videos, the participants were asked a series of yes or no questions about the moments in the videos when lies were told or sarcastic statements were made.

Of the 175 older adults who participated in the study, more than half of them had some sort of dementia. The healthy adults had no trouble detecting insincere speech, but people with frontotemporal dementia consistently failed to notice it. People with other forms of dementia, such as Alzheimer's disease and supranuclear palsy, performed better. In normal aging without neurodegeneration, the ability to discern between sincere and insincere communication does not deteriorate.

Researchers then created detailed MRIs of the participants' brains and found that those who could not detect lies had lesions in the brain's frontal lobes. In frontotemporal dementia, this part of the brain degenerates due to neuron death and the buildup of damaged proteins called tau.

Doctors may be able to use this correlation between extreme gullibility and brain degeneration to identify patients with frontotemporal dementia in the early stages of the disease. Early diagnosis is vital so that proper treatment and support can be provided.

The study's senior researcher, neuropsychologist Katherine Rankin, and her colleague from the UCSF Memory and Aging Center, Tal Shany-Ur, presented the results of the study at the 2011 Annual Meeting of the American Academy of Neurology.

Frontotemporal Dementia

Frontotemporal dementia is the most common form of dementia in adults under the age of 60. There are three distinct varieties of this disease. In the early stages, people tend to undergo extreme personality changes or exhibit inappropriate behaviors. Frequently, these early symptoms are misinterpreted as the evidence of a severe midlife crisis or depression. As the disease progresses, however, frontotemporal dementia robs sufferers of the capacities to empathize, reason, and communicate. Patients lose the ability to carry out both the complex activities of daily life—handling money or behaving in socially appropriate ways—and the simplest activities—such as eating and bathing.

This study offers important new insights into the earliest warning signs of this devastating condition.