“Viewing porn shrinks the brain,” reports the Daily Mail.

In a small study, MRI scans found that men who watched the most pornography had less grey matter – complex brain tissue – compared to men who watched the least.

It found a weak to moderate correlation between the number of hours of porn viewed a week and smaller and less active areas of the brain associated with reward and sexual stimulation in men.

The higher the number of hours of porn watched, the smaller the volume of grey matter and brain signalling.

In essence, the researchers thought this might be a sign “porn users” may be dampening down the sexual stimulation and reward centres in their brain through over stimulation.

However, one of the big issues with studies like this is that you can’t tell cause and effect. This could point to a somewhat unusual ‘chicken and egg situation’. It could be the case that men with weaker, smaller and less active areas of the brain crave greater stimulation so they are more likely to watch more porn.

In conclusion, this study does not provide any convincing evidence that viewing porn shrinks the brain, but tentatively highlights a possibility that it might.

Where did the story come from?

The study was carried out by researchers from the Center for Lifespan Psychology in Berlin, Germany and was funded by the German Federal Ministry of Education and Research (BMBF). The study was published in the peer-reviewed medical journal JAMA Psychiatry.

Generally, the media reported the story accurately, although the Mail’s actual reporting of the study was accurate, its headline that “viewing porn shrinks the brain” was overly certain as no cause and effect relationship was proven.

What kind of research was this?

This was a cross sectional study to determine whether frequent pornography viewing was associated with the frontostriatal network – an area of the brain associated with reward seeking, novelty seeking and addictive behaviour.

The researchers say that since pornography appeared on the Internet, the accessibility, affordability, and anonymity of consuming visual sexual stimuli have increased and attracted millions of users.

Incredibly, one study estimated that around 50% of all internet traffic is pornography-related.

They indicated that pornography consumption has elements of reward-seeking, novelty-seeking and addictive behaviour. They hypothesized that people watching a lot of porn may overstimulate these areas. So, as a natural counterbalance, this might lead to the dampening down of these brain responses. Similar to the way a drug addict might need higher doses to get the same effect as the body adapts.

The research looked to see whether the size and function of specific parts of the brain related to these behaviours were different across different levels of porn viewing.

One of the big issues with studies like this is that you can’t tell cause and effect or which came first. For example, the study can’t tell us whether watching porn leads to brain changes or whether people born with certain brain types watch more porn.

A longitudinal study, where participants are tracked over time, would be needed to investigate this fully.

What did the research involve?

The study recruited 64 healthy men between the ages of 21 and 45 years and asked them questions about their porn viewing habits.

They also took images of the men’s brains to determine the size of different areas and investigated how their brain signalling reacted to pornographic pictures using brain scans.

Two questions were used to estimate and categorise porn consumption across a full week:

“How many hours on average do you spend watching pornographic material during a weekday?”

“How many hours on average do you spend watching pornographic material during a day of the weekend?”

Additional questionnaires assessed other factors the researches thought might influence the results, including:

sexual use of the internet

sexual addiction

internet addiction

signs of psychiatric disease

substance use

depression

The study only recruited men, the rationale given by the researchers was that men are exposed to pornography at a younger age, consume more pornography, and are more likely to encounter problems related to it compared with women. This seems like a reasonable assumption based on what we know about pornography consumption.

Those with abnormal brain scans were also excluded from the study, as were those with medical or neurological disorders.

The main statistical analysis looked for links between weekly measure of porn consumption (pornography hours) and the volume and function of specific areas of the brain.

What were the basic results?

The average porn viewing estimate was four hours a week, ranging from 0 to 19.5 hours. The findings grouped into those assessing the structure of the brain and those assessing the signalling and function of the brain.

Structural brain volume

They found that higher number of hours viewing porn correlated with a reduction in grey matter in an area of the brain called the right caudate nucleus. This association remained after eliminating a second correlation with internet addiction and sexual addiction. An association was also found between higher porn consumption over many years and less grey matter in this brain area. The researchers interpreted this as a sign of the effects of longer-term porn exposure.

Functional brain signalling in reaction to pornographic images

From this set of experiments the researchers found the men reporting more porn consumption had less brain signalling within the left dorsolateral prefrontal cortex (DLPFC) of the brain implicating, the researchers say, that participants who consumed more pornographic material had less connectivity between the right caudate and left DLPFC.

They also implicated an area of the brain called the left putamen as involved in processing sexual content.

How did the researchers interpret the results?

The researchers concluded the grey matter volume in the right caudate of the striatum “is smaller with higher pornography use”. They said that there is a lot of research suggesting the striatum is important in reward processing. So taken together they believed this supported their theory that “that intense exposure to pornographic stimuli results in a down regulation of the natural neural response to sexual stimuli.”

Conclusion

This small structural and functional brain study indicates there might be a correlation between more hours of porn viewed a week and smaller and less active areas of the brain associated with reward and sexual stimulation in men.

In essence, this suggests porn users might be dampening down the sexual stimulation and reward centres in their brain through over stimulation.

One of the big issues with studies like this is that you can’t tell cause and effect or which came first, an issue the study authors recognised. For example, the study can’t tell us whether watching more porn leads to changes in reward and sexual stimulation centres in the brain, or whether people born with brains wired for high reward and sexual stimulation will watch more porn. A longitudinal study would be needed to untangle cause and effect.

In addition, although a correlation existed it was not particularly strong, on a scale of 1 (perfect correlation) to 0 (no correlation) the correlation (strength of the link) between porn hours and grey matter volume was 0.432.

This estimate may also be subject to error from confounding, error in categorising porn use from self-reports, and bias from other sources.

Related to this is the fact the study recruited relatively few men (64). A study with many more people would give evidence that is much more reliable and would be able to validate whether this correlation is real and what its true size might be.

The authors put forward a clear and intriguing rationale for their research and findings “pornography exposure might lead to wearing and down regulation of the underlying brain structure, as well as function, and a higher need for external stimulation of the reward system and a tendency to search for novel and more extreme sexual material”.

However, this research study alone does not prove this is the case, and warrants further study; especially due to the massive increase in pornography consumption that has accompanied the growth of the internet.

There is scant evidence on the pros and cons of pornography to physical or mental health, a research void that will hopefully be filled in the future. However, there is some evidence that porn can be addictive and evidence withstanding, is unlikely to be a substitute for a loving relationship.

Analysis by Bazian

Edited by NHS Website