It's important to know how the brain functions in healthy people

Dr Jerome Redoute

Jerome Redoute and his team at a research institute in Lyon, France, looked at nine healthy heterosexual men, and reported their results in the journal "Human Brain Mapping".

As well as engaging the PET scanner, which can detect activity wherever it happens in the brain, they measured the men's testosterone levels, heart rate and blood pressure.

Men were asked to assess the pictures and say whether they found them arousing or simply amusing.

Dr Redoute said: "The aim of the study was to show the brain region directly linked with visual sexual stimulation.

"We found that the activity of the claustrum was directly linked with the intensity of the sexual arousal.

"It's important to know how the brain functions in healthy people to understand what happens when men have sexual problems."

The claustrum is a small area of the brain, part of the "temporal lobe", found at the base of the brain.

Other studies have associated the rest of the lobe with a variety of functions such as language processing, and even spiritual and emotional feelings.

Many scientists are probing the mind with electronic scanners to try to work out what does what.

The claustrum is not the only area of the brain which has now been linked with sexual arousal - but appears to be one of the most important.