Compulsive sexual behaviour, more commonly known as sex addiction, is driven by the huge novelty provided by online material, a new study has found.
With the proliferation of online pornography, there's increasing concern surrounding the mental and physical health impacts, including the potential for addiction.
A key component in these addictions is a loss of control faced by sufferers, often with serious consequences to jobs and relationships.
In the study, published this week in the Journal of Psychiatric Research, twenty-two 'sex addicts' and forty 'healthy' controls were asked to choose between matched pairs of images in a series of tasks.
In the first task, volunteers were asked to pick between novel and familiar image pairs of naked women, clothed women, and items of furniture.
When presented with a choice between novel and more familiar sexual images, the sex addicts were more likely to pick the novel image over the neutral images.
Brain scans carried out at the same time identified a decrease in activity in a region called the dorsal anterior cingulate cortex, which is known to be involved in anticipation and novelty. This decrease in brain activity was larger among the sex addicts than the healthy participants.
It's similar, the researchers speculate, to the way that coffee delivers progressively smaller kicks as more cups are consumed over time. Addicts constantly crave novel images to boost brain stimulation.
"Knowing that with online pornography, or in fact any online materials, there is significant vast access to novelty," explains Dr Valerie Voon, a co-author from the University of Cambridge. "Does that novelty play a role in terms of driving some of these behaviours?"
It seems the answer is "yes," the endless supply of new material online sustains a high level of reward and keeps addicts coming back for more. "But where is their self control?" I hear you ask.
In the second task the images presented were a naked woman and a grey box overlaid with abstract images. These images were shown repeatedly to volunteers so they learnt to associate the abstract images with those underneath.
This process is similar to that in Pavlovís famous experiment where a dog learnt to associate a neutral stimulus, a ringing bell, with a reward, food. When the bell rings, even without the food present, the dog salivates.
When asked to chose between the learnt abstract images and a new abstract image without the presence of the overlaid images, the sex addicts were more likely to chose the image previously associated with a sexual cue.
Sex addicts may not be aware or able to control their response to cues that trigger them to seek out sexual images. Triggers may be as simple as switching on a computer, loading up an internet browser or seeing an attractive woman and can be extremely difficult to avoid in everyday life.
We can all sympathise with spending hours online. You may have found yourself browsing the internet, finding plenty of new and rewarding content on The Naked Scientists website, for instance. Dr Voon thinks her research on novelty and cues may be more widely applicable.
"I think this is something that may be a mechanism that may be generalisable to compulsive use of any kind of internet material whether itís social media or whether itís looking at news outlets..."