Being gullible or unable to work out when someone is being sarcastic could be an early sign of dementia, research has revealed.
Scientists at the University of San Francisco asked several older people with neurodegenerative conditions, and others without, to analyse videos of people talking either frankly or lying.
Using MRI scans, researchers were able to find links between declines in some parts of the brain and a person's inability to detect insincerity, according to findings presented at the American Academy of Neurology meeting in Hawaii.
Senior author Katherine Rankin said of the study: "These patients cannot detect lies.
"This fact can help them be diagnosed earlier."
Meanwhile, research published in journal Radiology has indicated that an MRI scan could be used to predict which cases of mild cognitive impairment are likely to develop into Alzheimer's disease, meaning the condition could be forecast years before onset.
According to the study, brains which exhibit a pattern of cortical thinning are more likely to develop Alzheimer's disease.