Grumpy old men as portrayed in Hollywood can cuss their way out of any jam, but the hard reality is the elderly are cream puffs for scam artists and unscrupulous family members.

The U.S. Government Accountability Office calls elderly financial abuse an epidemic that undermines the health of older Americans. It estimates that older adults were defrauded out of at least $2.9 billion in 2010, forcing tax-supported safety nets to step in to cover the cost of their health care.

Now, new research is showing for the first time that age-related changes in the brain may leave older adults particularly vulnerable to fraud.

In a University of California, Los Angeles study, two dozen young volunteers between 20 and 42 and more than 100 adults who were 55 or older were hooked up to sophisticated brain scanners and shown pictures of faces.

Some of the faces were normal and sincere.

Others were more like Snidely Whiplash from Dudley Do-Right, with averted eyes, forced smiles and unnatural head tilts intended to trigger suspicion … although none of them actually twirled a handlebar moustache.

When younger volunteers saw a smarmy face, an area of their brains associated with emotional reactions and gut instincts lit up. The same region in older adults was dark.

Younger adults far more readily identified the untrustworthy faces, while older adults tended to view most of the faces as trustworthy … even the suspicious ones.

Both groups rated trustworthy and neutral faces about the same.

Researchers aren’t sure whether older people pay less attention to facial clues, or whether their brains can’t process the warning signals.

But knowing why people increasingly view dishonest faces as trustworthy as they get older may be useful in the development of strategies for healthy cognitive aging.