Washington, April 17 (IANS) Getting the aged to analyse videos of chatting people would show up whether they are able to detect sarcasm and lies and so help diagnose degenerative diseases like dementia and Alzhemier's early on.

A team from the University of California in San Francisco mapped their brains using magnetic resonance imaging (MRI), which showed linkages between the deterioration of particular brain regions and the inability to detect lies.

"These patients cannot detect lies," said study co-author and neuropsychologist Katherine Rankin, member of the San Francisco Memory and Aging Centre. "This fact can help them be diagnosed earlier."

Rankin and her postdoctoral fellow Tal Shany-Ur showed how it may be possible to spot people with particular neurodegenerative diseases early just by looking for the telltale sign of their inability to detect lies, according to a university statement.

Rankin and her team surveyed 175 people, more than half of whom had some form of neuro-degeneration. They showed them videos of two people talking, one of whom would occasionally tell lies or use sarcasm, made apparent by verbal and non-verbal cues. Then the test subjects were asked "yes/no" questions about the videos.

Healthy older people in the study could easily distinguish sarcasm from sincere speech. However, subjects with dementia were less able to discern among lies, sarcasm, and fact, the team found.

The finding was presented Saturday at the 63rd Annual Meeting of the American Academy of Neurology in Hawaii.