Time to resolve that cliffhanger I left you with yesterday – since when, incidentally, Heretic TOC’s hit rate has jumped significantly: seems a bit of controversy is good for business!

So, where was I? Ah, yes, I said a neuroscientist had agreed with Susie Orbach and myself that there was good reason for skepticism over a theory that paedophilia is caused by “crossed wiring” in the brain. An MRI scanning study by James Cantor and his team into the brains of paedophiles and others had shown that paedophiles have less “white matter”, this being interpreted as a dysfunctional deficiency.

Before going into the details, it might be an idea to point out that there are good reasons for not jumping to conclusions about “deficiency” based on measurements of gross brain anatomy. Not so long ago it was thought women must be less intelligent than men because their brains are smaller, but this is classically a field of study in which size really isn’t everything: the average brain weighs around 1.4kg. Einstein’s weighed only 1.2kg. True, he had more white matter than most, so the extent of this tissue and how it is “wired” may indeed be hugely important. I gather that white matter is basically a load of lard: fat. The fatty sheathing for the axons, or long, message-carrying, tails of the brain cells, acts as an insulator and hence helps signals whizz around at speed from one part of the brain to another.

Something like that. Anyway, the main point of interest here is not so much what white matter does as what factors might influence changes in its volume, especially whether its size and density could change in response to what our brains are exposed to in daily life. In the case of London taxi drivers, we know that a part of the brain associated with memory, the hippocampus, grows considerably when they study for “the knowledge” i.e. the detailed knowledge of the streets of London they must acquire to pass their exam and get their cabby’s licence. This is grey matter rather than white matter but, no matter, the changeability, or “plasticity”, of the brain could apply to various parts.

And now, at last, what really matters, who is this mystery neuroscientist I have recruited as an ally, and what does he say? Well, all I know – so it really is a bit mysterious – is that he works in the UK and is a highly respected blogger operating under the does-what-it-says-on-the-tin monika of Neuroskeptic. As he puts it, “A neuroscientist takes a skeptical look at his own field, and beyond.”

I emailed him in the hope of discovering whether my amateur speculations as to potential weaknesses in Cantor’s work might possibly have some substance. I was not disappointed. Here is what he wrote in reply, last month:

Hi Tom, many thanks for your email & extremely astute comments. Essentially I agree on all counts. I may well post about this because it’s pretty important: the extra arm analogy is just misleading. cheers, NS

Ah, the “extra arm analogy”!

OK, dear readers, if you want to know what that is all about, and I hope you do, you will need to settle down comfortably and give the exercise some quality thinking time. So take a break at this point, if necessary, and come back to it after.


An interesting study in this area was J.M. Cantor et al.’s sMRI paper “Cerebral white matter deficiencies in pedophilic men”. Journal of Psychiatric Research, Volume 42, Issue 3, Pages 167-183 (2008)

The study looked for brain regions that distinguish pedophilic from nonpedophilic men. Pedophiles were found to have less white matter. The authors suggested that the regions in question operate as a network for recognizing sexually relevant stimuli and that pedophilia results from a partial disconnection within that network.

The work is one of a series of papers purporting to indicate that pedophiles have brain deficiencies resulting from “perturbation” of prenatal development, and other misfortunes such as trauma from childhood head injuries. Papers have shown lower average IQ of pedophiles and far more left-handedness than average.

Leaving aside methodological problems with the IQ etc. studies, I would be interested to know whether Neuroskeptic sees any grounds for scepticism over this white matter paper. Is it just the new phrenology or something more substantial?

The thing is, the speculation offered about the said white matter “deficiencies” (Does anyone know how much white matter is sufficient?) does not appear to offer any particular explanatory model for causing paedophilia. Is there an issue here as regards direction of causation? Could paedophilia cause changes in brain anatomy, rather than the other way around?

Writing about structural MRI studies, including his own, of paedophilia, in an article aimed at non-specialists in this field, James Cantor acknowledged the question mark over direction of causation, and explained his own thinking:

When comparing pedophilic and nonpedophilic men, one must remain careful not to confuse cause with effect. That is, one must consider carefully whether the brain differences we detected cause pedophilia or whether some aspect of being pedophilic caused the brain differences. Previous research findings suggests that it is more likely for the brain differences to be causing pedophilia than for the other way around: Although it is now known that certain brain structures respond to environmental stimulation, such as the motor cortex, there is no evidence that such stimulation causes any changes in the superior fronto-occipital fasciculus or right arcuate fasciculus (the brain regions in which pedophiles and nonpedophiles differ). Moreover, the brain regions we identified are extremely large, and no previous research has ever found changes in such large regions of the brain. As an analogy, physical exercise will generally stimulate one’s muscle tissue to grow, but one would not grow an extra arm; neurological changes occur only in a very specific manner.” http://individual.utoronto.ca/james_cantor/blog2.html

The analogy of the extra arm is a vivid and plausible one, but is it really valid? At a time when, we are told, epigenetic discoveries are showing that environment can profoundly modify organisms’ biology, might it be entirely possible, or even routine, for brain anatomy to be altered quite radically by unusual environmental influences? I am thinking here of unusual conditioned responses to sex pheromones emitted by fellow humans. In the case of pedophilia, this would mean sexual arousal to child-related sensual stimuli (visual, auditory, tactile, etc.) once these had been conditioned from an association with the pheromone, this being theoretically the primary (olfactory) stimulus.

Genetically identical bees vary enormously from each other both in physical form and the roles they play. The queen can be twice the size of a worker bee. Workers typically have a lifespan of only weeks, whereas a queen can live for years. Also, the differences in the roles played by workers as opposed to queens are many and complex. As the genome is exactly the same for these massively differentiated types of bee, the differentiation would appear to arise from different patterns of gene expression.

If similar processes are at work in humans (not such a big “if”, it seems, given the fundamental cross-species nature of the molecular mechanisms involved) might not pheromone-mediated changes in gene expression within the brain be capable of giving rise to lasting and quite large changes in brain anatomy, such as different white matter structure for those experiencing pedophilia? If this is the equivalent of growing an “extra arm”, epigenetics seems potentially entirely capable of being up to the task.

Does Neuroskeptic agree?