FTD patients cannot detect sarcasm

I really love coming to visit you, Grandpa.

Researchers at the University of New South Wales are using sarcasm to determine whether patients have frontotemporal dementia (FTD), otherwise known as Pick's disease:

Researchers at the University of New South Wales found that patients under the age of 65 suffering from frontotemporal dementia (FTD), the second most common form of dementia, cannot detect when someone is being sarcastic.

The study, described by its authors as groundbreaking, helps explain why patients with the condition behave the way they do and why, for example, they are unable to pick up their caregivers' moods, the research showed.

"This is significant because if care-givers are angry, sad or depressed, the patient won't pick this up. It is often very upsetting for family members," said John Hodges, the senior author of the paper published in "Brain".

"(FTD) patients present changes in personality and behaviour. They find it difficult to interact with people, they don't pick up on social cues, they lack empathy, they make bad judgements," he told AFP.

...

The research, conducted in 2006-07, put 26 sufferers of FTD and 19 Alzheimer's patients through a test in which actors acted out different scenarios using exactly the same words.

While in one scenario, the actors would deliver the lines sincerely, in others they would introduce a thick layer of sarcasm. Patients were then asked if they got the joke, Hodges said.

For example, said Hodges, if a couple were discussing a weekend away and the wife suggested bringing her mother, the husband might say: "Well, that's great, you know how much I like your mother, that will really make it a great weekend."

When the same words were delivered sarcastically and then in a neutral tone, the joke was lost on FTD patients, while the Alzheimer's patients got it.

I wasn't able to find the article in Brain yet because I don't think it is out yet, but here is a similar article on the subject.

A couple comments: Pick's disease is really rare. If you have a relative with dementia odds of overwhelmingly that it is Alzheimer's and not FTD. But it is an interesting finding that patients with FTD fail to understand sarcastic statements while patients with Alzheimer's do.

I guess my question would be, what is the mechanism of perception of sarcasm? It must be the perception of some disconnect between the speaker's perceived intention and their actual statements. We know that mirror neurons -- neurons that are active when you perceive someone else performing a task, neurons that we think are involved in empathy -- are in the frontal lobes, so the loss of these neurons may explain the phenotype. However, at end stage Alzheimer's you also see frontal lobe issues. Maybe there is a stage in Alzheimer's where you would also see loss of sarcasm, although likely by that point they aren't doing much talking anyway.

The most bizarre part about all of this is the thought of putting into practice. Could you visualize going into a patient's bedroom and being sarcastic to see if they had FTD? What if they didn't? You would look like such a jackass.

Furthermore, I know a bunch of healthy people who don't understand sarcasm either. What do you make of them?