How does this make you feel? Simply asking people to think about emotion-laden actions as their brains are scanned could become one of the first evidence-based tests for psychiatric illness.
Assessing people in this way would be a step towards a more scientific approach to diagnosis, away from that based on how someone behaves or how they describe their symptoms. The US National Institute of Mental Health has had such a goal in mind since 2013.
Marcel Just of Carnegie Mellon University in Pittsburgh, Pennsylvania, and his colleagues developed the brain scanning technique and used it to identify people with autism. "This gives us a whole new perspective to understanding psychiatric illnesses and disorders," says Just. "We've discovered a biological thought-marker for autism."
The technique builds on work by the group showing that specific thoughts and emotions are represented in the brain by certain patterns of neural activation. The idea is that deviations from these patterns, what Just refers to as thought-markers, can be used to diagnose different psychiatric conditions.
Hugging or watching?
The team asked a group of adults to imagine 16 actions, some of which required emotional involvement, such as "hugging", "persuading" or "adoring", while they lay in an fMRI scanner.
When people with autism contemplated these emotion-laden words, neighbouring regions of the brain called the posterior cingulate and one called the precuneus were much less active than in people without the condition. An algorithm was then used to identify who has autism on the basis of such brain activity patterns.
When Just tested the system on 34 people – 17 with and 17 without autism – it successfully guessed whether they had the condition for all but one person, a 97-per-cent success rate.
It works because the posterior cingulate and the precuneus are the brain's hub for self-referential thought. "When asked to think about persuading, hugging or adoring, the neurotypical participants put themselves into the thoughts; they were part of the interaction. For those with autism, the thought was more like considering a dictionary definition or watching a play – without self-involvement," says Just.
Underlying mechanism
A similar approach may be applicable to other mental illnesses, says Just. "We are currently running a small pilot study in another psychiatric disorder, and so far it looks promising," he says.
For now though, the results need to be repeated in a larger independent trial before we know if it works for autism, let alone other conditions, says Simon Baron-Cohen, director of the Autism Research Centre at the University of Cambridge.
"Psychiatric diagnoses are a huge burden to the individual and society and there is growing recognition that our current classifications, based upon self-reported symptoms, can lead to poor treatment outcomes for many individuals," says Oliver Robinson from University College London.
"Where approaches such as this hold promise is in clarifying the underlying mechanistic problems in the disorders, which we may eventually use to develop better treatments, and to get those treatments to the right people," Robinson says. However, the clinical use of such techniques is still quite a way off, he says.
Journal reference: PLoS One, DOI: 10.1371/journal.pone.0113879
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Up, down, left, right: our brains map exactly where we are in the world (Image: Mihaela Ninic/plainpicture) 
