Hardcore Neuro-Porn

By Neuroskeptic | October 3, 2013 6:12 pm

Britain’s been talking about pornography this week. On Monday, Channel 4 broadcast Porn on the Brain, accompanied by plenty of excited press coverage.

Porn is hardly a recent invention. So what’s new?

It all centres on this:

In an fMRI study conducted at Cambridge University, and discussed in the Channel 4 documentary, healthy controls and compulsive porn users were shown sexual images.

The brains of porn users showed more activation – and the region differentially activitated was the reward system, the same area activated by addictive drugs.

The media were attracted to those little yellow blobs:

Scan images show that watching online ‘adult’ sites can alter our grey matter [this is not what fMRI shows in any case], which may lead to a change in sexual tastes

This hasn’t been published in a peer-reviewed journal yet, so we can only judge by what we see.

First off, the areas of activation are more block than blob, with lots of sharp edges, unusual for fMRI. The brain is not made of lego, so you don’t expect to see corners in there.

On Twitter, it was suggested that it might just be an honest reflection of the fact that fMRI images have less resolution than structural images (the grey brain). But the resolution of the blobs is actually pretty high, when you look closely.

To me, this suggests that the functional images have been masked, to hide activations outside of a particular, defined region.

Here’s where I suspect that the mask was – the blue boxes are in the same place on the top and the bottom row. This would explain why some of the edges line up across the two groups.

I might be wrong. Even if I’m right, there’s no neuroimaging law against masking. It’s a perfectly legitimate technique when used appropriately, but in this case it matters – it might change our interpretation of the differential activation in the porn users, if we could see that it wasn’t selective to the reward system.

For instance, if the brains of users lit up in the visual cortex, as well as the reward areas, then that might suggest that rather than being addicted to pornography, the users were just looking at it more closely. Perhaps, having seen it all before, they were less prone to averting their eyes than the more bashful controls.

Or alternatively, it could be that the users’ brain activity reflects the emotions of shame or guilt they feel at being confronted with their weakness – in which case, emotion and self-concept-related circuits might well light up too.

Or it might be that the users’ brain response was just heightened overall because they were breathingly more heavily, causing changes in the blood oxygenation that fMRI uses as a proxy for brain activity.

In fact, all of these interpretations are possible even if there wasn’t any masking.

But supposing there was indeed a selective (and statistically significant) difference in brain response in the reward area – supposing it were proven to be a consequence of porn use and not a preexisting risk factor – where would that leave us?

We neuroscientists would get an interesting finding – another data point to ponder in our attempts to figure out what these areas of the brain do. But normal people expecting a ‘take home message’ will be disappointed because as of yet, we’re just not sure what most brain activity means.

‘What porn does’ is not a question neuroscience can answer yet. A brain scan won’t tell us; if anything can, it’s one of the few human inventions older than pictures of naked people – observing and thinking about human behaviour.

  • jordanyutes

    I suggest watching the actual documentary before “guessing” – as Dr. Valerie Voon shows more regions of the brain and describes how the other regions differ from controls, and how they resemble cocaine addicts.

    I think Voon knows what she is doing when it comes to addiction and neuroimaging.

    • http://blogs.discovermagazine.com/neuroskeptic/ Neuroskeptic


      1) My hypothesis was correct – the image was masked. In the documentary we see that other components of “the reward network” lit up as well – but if so, this network might itself be masked and the rest of the brain might be behaving differently as well.

      This seems likely because what is being shown seems to be a within-groups contrast of porn stimuli vs. some baseline or neutral stimuli, rather than a between-groups difference of users vs healthy controls.

      In which case, it would be odd if only the “reward network” lit up (in any population), you’d expect some more posterior brain activation, if only occipital activation due to differences in the visual properties of the images.

      I ‘guess’ therefore that we don’t know what was happening in the rest of the brain. Making it possible that my hypothetical alternative explanations were correct. But maybe not. We don’t know.

      2) I have no doubt that Dr Voon is an excellent researcher which is why I didn’t name her in my critical post. But good scientists have been known to get things wrong and I have no doubt that Dr Voon would not approve of arguments from authority.

      3) “Care to cite a study that shows that “guilt” increases the activation of the nucleus accumbens?”

      I said that if guilt/shame was at play, you would expect other areas to light up as well, namely emotion and self-concept related areas. Lo and behold, they did (20:17 in the PotB video) in the amygdala, insula and cingulate. Now guilt is surely not the whole explanation for all the blobs.

      But supposing you just focussed on (and masked) those guilt areas, you could plausibly claim that it indicated that those people were repelled by porn and hated it. See my point…?

      4) We are indeed not sure what increased nucleus accumbens activity means. We know a lot about the nAcc I agree, relatively speaking; I have published an fMRI paper on it myself. But we can’t infer, from a difference in BOLD signal in that area, what it means in real world terms.

      In this case, we could at best infer that something to do with reward processing of the pornography is different in the compulsive porn using men. But we could have already reasonably inferred that from the fact that they were compulsive porn users. What it wouldn’t tell us is whether the difference was i) a preexisting trait marker of porn vulnerability ii) a consequence of porn use but one not related to any possible ‘addiction’ (e.g. reflecting a conditioned response due to regular viewing of porn) iii) a consequence of porn use related to ‘addiction’…etc

      In order to find out we would need to compare heavy compulsive porn users, to heavy non-compulsive non-‘addict’ users, and ideally I would throw in some porn stars, or porn magazine editors, to see whether any differences are driven by familiarity with porn (nAcc codes salience: http://www.ncbi.nlm.nih.gov/pubmed/23678119) rather than liking per se…

      I’m not criticizing Voon’s study. I said we’ll have to wait until it is published and when it is I’m sure it’ll be very interesting (sincerely). But it is experimental science, not a guide to social policy. Maybe in 10 years we’ll reach that point. The documentary presented it as solid, ‘actionable’ fact. It is not.

      • jordanyutes

        You continue to discuss the Voon study as if it were the first ever fMRI study on addicts. The Voon study aligns perfectly with all the other fMRI cue-induced studies performed on drug and behavioral addictions published over the last 15 years, That is the true context, not the sideways analysis.

        Please note that over 50 Internet addiction brain studies have been published in that last few years that align with the Voon study. Many of these Internet addiction studies included porn users, and all the studies found data consistent with addiction.

        Your alternate theories on nucleus accumben activation don’t carry much weight, such as guilt, or a prexisting “trait marker”. The suggestion of a “conditioned response” is exactly what Voon was measuring – sensitization which is the core addiction chnage in the nucleus accumbens.

        As for the suggestion of comparing porn addicts to heavy porn users who are not addicts, how do you discern the difference? Assessment tests for “hypersuxality” cannot be applied to Internet porn user.

        • http://blogs.discovermagazine.com/neuroskeptic/ Neuroskeptic

          “As for the suggestion of comparing porn addicts to heavy porn users who are not addicts, how do you discern the difference?”

          Well, now that’s the question! We would first have to define the difference between “heavy use” of X and “addiction to” X. But that’s the whole point of my ‘we don’t know what nAcc means for addiction’ argument.

          There must be a difference between heavy use and addiction, otherwise the concept “addiction” would not carry the complex implications that it does.

          One might operationalize the difference by asking people how distressing they feel the use is, how many times they have tried to cut down, if they feel in control etc.

          That would allow you to find heavy non-addicted users.

          As it stands, all the difference compared to healthy controls tells us is that reward systems that have been heavily exposed to porn react differently to porn from those that haven’t (that’s assuming the difference is statistically significant and wasn’t accounted for confounding factors like attention etc.) – it doesn’t tell us that this is related to the addiction in ‘porn addiction’ in any meaningful way; it might be to do with the ‘porn’ instead, if you see what I mean.

          We certainly know from animal electro-physiology that the dopamine system is plastic and comes to fire in response to cues-for-rewards after conditioning even it starts out firing to rewards only.

          So maybe that’s all that’s going on here. Maybe porn is the cue and the primary reward is masturbation. In which case you’d expect to see altered reward activity to porn in heavy users but would that tell you anything about ‘addiction’ or just about heavy use? I think the latter. Unless you had a heavy-use-no-addiction group.

        • Anandamide

          Increased accumbal activation (and OFC activation, which I think was shown in the program) is seen in addicts but is very far from a neurological marker for addiction – NAc activity could be easily be representing greater pleasure and / or salience, both of which could (non trivially) be expected in people who report problematic porn viewing and neither of which are necessarily linked to addiction. OFC activation has been tied to salience (again) and assignment emotional valence, as well as being correlated with the experience of craving in abstinent drug users exposed to drug related cues. To be frank, I’m entirely unsurprised by these results, although I’m unsure what to make of them. The most boring conclusion is that people who regularly use porn get more enjoyment from it and value it. Or, conversely, that people who get a lot of enjoyment from porn and attach a greater degree of value to it are likely to watch a lot of it.

          Ultimately, the hallmark off addiction remains problematic use (i.e negative impact on other life goals) and risk of relapse. These brain scans don’t show that, because *no* brain scans show that – addiction can only be determined behaviourally. But, of course, the media fetish for fMRI means that such behavioural measures are never good enough. It is a prime example of ‘neuro realism’. The methods for determining if ‘internet porn addiction’ is a ‘real’ disease entity are behavioural assessments, interviews and questionnaires; this is also how one would determine ‘heavy porn users’ from ‘addicts’. It would make for better science – but it wouldn’t make for good TV.

  • chomps

    Is it not possible that the rest of the brain activity is the same, or shows such trivial difference that it made more sense to highlight only what was different? Isn’t that usually what highlighting is for? I mean, obviously if there are differences elsewhere, it’s important, but it seems to be fairly straightforward to me.

  • Artem Kaznatcheev

    “This hasn’t been published in a peer-reviewed journal yet, so we can only judge by what we see.”

    Should we not judge by what we see after it’s been peer-reviewed? Is rational evaluation of evidence no longer necessary after three semi-anonymous people in a non-transparent process vetted a paper as “acceptable”? This fetishization of peer-review is as bad as the fetishization of neuro-images, and is leading to an ever-expanding bottom tierof awful awful journals draining resources and respectability just to give a false stamp of ‘reviewed’.

    Sorry for going off topic!

    • guy incognito

      i think he just meant that since it hasn’t been published, he can’t check for methodological details such as whether the pictured contrast was masked or not.

      • http://blogs.discovermagazine.com/neuroskeptic/ Neuroskeptic


  • robbety

    Essentially means nothing. People who like porn are more excited when they look at porn than non-porn people. You could do the same study with friggin vanilla milkshakes.

  • Nick Stuart

    Fantastic news! With this new technology we can now accurately pin point which circuits of the brain we can force zap in order to introduce the New Moral Order. Shame we did not have this when masturbatory insanity and homosexuality were considered mental diseases. (Of course you missed the big question. Why the hell are neuroscientists doing this research… are they the new psychiatrists?)

  • Anna O

    I am always struck by the circular rationale used to explain the differences in the pattern of brain activity in most between-groups studies (on virtually any topic).

    Imagine if the brain activity between the two groups was significantly different, but only the other way round – i.e., in the compulsive porn user group, the NA activity was lower than in the control group. Then the spin would have been something along the lines of “reduced sensitivity” or “hyporeactivity” in the brains of compulsive porn users.

    • Wouter

      Yeah, you’re completely right. However, there’s a weak but valid excuse for this sort of reasoning; practically, we’ve got no clue what exactly, and how, the brain does what it does. So virtually any neuroscientific outcome will be interpreted as supporting or underlying some behaviour.
      On the plus side, we do go forward with studies like these. It is going to be harder for future studies to reason the other way around, if multiple studies have already reported an effect supporting a particular interpretation.

  • Y.

    Slightly off-topic: Neuroskeptic, in what situations do you think masking would be appropriate? Thanks.

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  • PeterJ42

    A control is essential here. “Porn” is watching sexual activity remotely, via video or still pictures.
    A map of brain activity when watching the reality will tell us much more. As will brain activity while actually being involved.

    But it seems to me that the documentary – and the writer here – has fallen into the bear pit of pseudoscience – being more interested in the headlines than the research. It didn’t do the work of defining porn – to one person an illicit view of an ankle can be porn, to another (well I’ll leave that to your imagination). The brain will work off that person’s in-brain definition on what stimulates them.

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About Neuroskeptic

Neuroskeptic is a British neuroscientist who takes a skeptical look at his own field, and beyond. His blog offers a look at the latest developments in neuroscience, psychiatry and psychology through a critical lens.


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