The results show that people diagnosed with anxiety are less able to distinguish between a neutral, 'safe' stimulus (in this case, the sound of a tone) and one that was earlier associated with the threat of money loss or gain.

In other words, when it comes to emotional experiences, they show a behavioral phenomenon known as over-generalisation, researchers said.

"We show that in patients with anxiety, emotional experience induces plasticity in brain circuits that lasts after the experience is over," said Rony Paz from Weizmann Institute of Science in Israel.

For the study, researchers trained people with anxiety to associate three distinct tones with one of three outcomes -money loss, money gain, or no consequence.

In the next phase, participants were presented with one of 15 tones and were asked whether they had heard the tone before in training or not. If they were right, they were rewarded with money.

The best strategy was not to mistake (or over-generalise) a new tone for one they had heard in the training phase. But researchers found that people with anxiety were more likely than healthy controls to think that a new tone was actually one of the tones they had heard earlier.

That is, they were more likely to mistakenly associate a new tone with money loss or gain. Those differences were not explained by differences in participants' hearing or learning abilities. They simply perceived the sounds that were earlier linked to an emotional experience differently.

Functional magnetic resonance images (fMRIs) of the brains of people with anxiety versus healthy controls showed differences in brain responses, too.

The findings might help to explain why some people are more prone to anxiety than others, although the underlying brain plasticity that leads to anxiety isn't in itself 'bad.'

The findings were published in the journal Current Biology.

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