A brain surgery patient was cured of arachnophobia following an operation but developed a temporary aversion to music.
Dr Nick Medford, a senior lecturer in psychiatry at the Brighton and Sussex Medical School (BSMS), and medical student Sophie Binks, made the discovery, the first of its kind, after observing a patient who had started having seizures and was found to have swollen tissue in part of his brain.
As a result, he had to have his damaged left amygdala - which helps to process emotions such as fear, anger and pleasure, and determine what memories are stored - removed, a BSMS spokesman said.
When the patient recovered from surgery he found that his fear of spiders had disappeared, and instead he started to find them "fascinating".
Dr Medford said he believes the phobia could have been cured while leaving normal response fear intact because humans have two different types of fear response.
He said: "It's like when you see a snake and you jump back in alarm, but when you look back you realise it's just a stick.
"That's your quick panic response: it isn't very accurate but it's necessary for basic survival.
"Then there's the more nuanced fear-appraisal which takes longer to process but is more accurate."
A paper detailing the case has been published in the journal Neurocase: The Neural Basis of Cognition.