What is it like to have never felt an emotion?

Caleb is telling me about the birth of his son, now eight months old. "You know you hear parents say that the first time they looked at their kid, they were overcome with that feeling of joy and affection?" he asks me, before pausing. "I didn't experience any of that."

His wedding day was equally flat. To illustrate his point, he compares it to a Broadway show. In front of the stage, he says, the audience are transported by the drama. Look behind the scenes, however, and you will find the technical engineers, focusing on analysing the technicalities of the event.

Despite taking centre stage at the ceremony, he felt similarly detached from the tides of emotion swelling up in the people around him. "For me, it was a mechanical production," says Caleb (who asked us not to use his full name). Even as his wife walked down the aisle, the only sensation he felt was his face flushing and a heaviness in his feet; his mind was completely clear of joy, happiness, or love in its conventional sense.

In fact, Caleb claims not to feel almost any emotions - good, or bad. I meet him through an internet forum for people with "alexithymia" - a kind of emotional "colour-blindness" that prevents them from perceiving or expressing the many shades of feeling that normally embellish our lives. The condition is found in around 50 per cent of people with autism, but many "alexes" (as they call themselves) such as Cal­­­eb do not show any other autistic traits such as compulsive or repetitive behaviour.

Getting to the bottom of this emotional blindness could shed light on many serious illnesses, from anorexia and schizophrenia to chronic pain and irritable bowel syndrome.

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