COMPULSIVE users of porn show the same signs of addiction in their brain as those hooked on booze or drugs, according to researchers.

The brains of young men who are obsessed by online pornography 'lit up like Christmas trees' upon being shown erotic images, a pioneering study has found.

The area stimulated - the part of the brain involved in processing reward, motivation and pleasure - is the same part that is highly active among drug and alcohol addicts.

The Cambridge University research, the first of its kind in the world, coincides with a survey which revealed that watching porn online is the norm for boys as young as 13.

Campaigners have also warned that increasing porn use among teenagers warps their view of sex and prompts boys to treat girls as sex objects.

However, until now the actual effects of pornography on the brain have been unclear. Dr Valerie Voon, a Cambridge University neuroscientist specialising in addictions, studied 19 self-confessed compulsive pornography users. The men, aged 19 to 34, had tried and failed to break their habit and had lost relationships and jobs as a result.

All fed their habit using online porn. When they were shown erotic video clips, a part of their brains lit up called the ventral striatum.

It is the same part of the brain that springs to life when a drug addict sees a dealer or an alcoholic sees an advert for drink.

When they were shown non-erotic but exciting sports images, the men's brains reacted far less strongly.

Similarly, the reaction was weak in men who were not obsessed by porn.

Dr Voon plans to look at whether learning more about the brain will lead to new ways of treating or breaking an addiction to pornography. Her research will feature in documentary Porn On The Brain, presented by Martin Daubney, the former editor of lads' mag Loaded.

Mr Daubney spent a year talking to scientists, teenage boys and teachers for the documentary which will be screened next Monday.

"The age of innocence is over," he said. "The internet is now a rolling buffet of online depravity. Given what we now know about porn seemingly being addictive, it's like leaving heroin around the house for kids to take."

Some doctors have argued that heavy users of porn show the same traits of addiction as alcoholics and drug addicts.

In evidence to the United States Congress in 2008, psychiatrist Jeffrey Satinover said that "Modern science allows us to understand that the underlying nature of an addiction to pornography is chemically nearly identical to a heroin addiction: only the delivery system is different."

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