Individuals with neurodegenerative disease — Alzheimer’s disease and dementia are good examples — have a difficult time detecting lies and sarcasm, according to a study at the University of California, San Francisco.
The researchers asked a group of older adults (a mix of both healthy adults and those with neurodegenerative disease) to watch videos of conversations, some in which people were telling the truth and others in which they were not.
Using magnetic resonance imaging (MRI), the scientists were able to determine which parts of the brain govern a person’s ability to identify sarcasm and lies. The images revealed the associations between the deteriorations of particular parts of the brain and the inability to detect insincere speech.
“These patients cannot detect lies,” said UCSF neuropsychologist Dr. Katherine Rankin, a member of the UCSF Memory and Aging Center and the senior author of the study. “This fact can help them be diagnosed earlier.”
The research is part of a larger study at UCSF’s Memory and Aging Center examining emotion and social behavior in neurodegenerative diseases as a way to better predict, diagnose and prevent these conditions.
“We have to find these people early,” said Rankin. Overall, scientists suggest that early diagnosis will provide the best opportunity for intervention when drugs become available.
The ability to tell a lie from the truth resides in the brain’s frontal lobe. In diseases such as frontotemporal dementia, the frontal lobe is one of the areas that will continue to degenerate because of a build-up of damaged proteins known as tau and the death of neurons in those areas. People who age normally without neurodegeneration, on the other hand, generally do not suffer a significant decline in their ability to understand sarcasm and deception.
The frontal lobes are strongly associated with complex, higher-order human thinking; thus being unable to detect a lie is only one of several ways the disease may manifest itself. Early symptoms may include any number of differences in behavior, including acting out in socially inappropriate ways or experiencing fundamental shifts in beliefs — changing political views or religions, for example.
Ironically, these symptoms are often overlooked because they are misattributed to depression or a severe midlife crisis.
For the study, the research team recruited 175 volunteers, more than half of whom had some form of neurodegeneration. The participants watched videos of two people talking, one of whom would occasionally tell lies or use sarcasm — a fact that was made obvious through both verbal and non-verbal cues. Then the volunteers were asked yes and no questions regarding the conversations.
Healthy participants could easily tell the difference between sincere and insincere speech. However, those with frontotemporal dementia were less able to discern among lies, sarcasm and fact. Patients with different forms of dementia, such as Alzheimer’s disease, did a better job.
The scientists used MRI to generate extremely accurate images of the subjects’ brains. The images revealed that differences in the volumes of certain brain regions correlated with the inability to detect sarcasm or lying.
According to Rankin, the research should help raise awareness of the fact that severe gullibility can actually be an initial symptom of dementia — something that might help more patients be correctly diagnosed and receive earlier treatment.
“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.
Source: University of California