It seems like science journalists never shy away from a good headline. And by a good headline, I mean one that can prove controversial to the meandering eye of an unwary reader. Reported under the provocative title “Religious experiences shrink part of the brain” by Scientific American, and less dramatically elsewhere (Pacific Standard, MedicalXpress) is a study on how religiosity, it seems, might affect your hippocampus.

In a paper by Amy Owen and colleagues from Duke University, they investigated how the volume of your hippocampus, a small structure well tucked near the base of the brain and principally involved in memory and spatial navigation, might be related to your particular confession.

The idea is fairly straightforward: get a bunch of people, ask them where do they go for Sunday mass and scan their brains. The findings are fairly striking: self-report of a life-changing religious experience was related to smaller hippocampi. Also, those who identified as born-again Protestants, Catholics or not belonging to a religious group showed greater atrophy over time, compared to non born-again Protestants.

What does this tell us? In the author’s view these results are a showcase of complex social behaviour (religiosity) impacting our biology (hippocampal size). Owen highlights that the extra atrophy may be caused ‘by the stress of belonging to minority religious groups – since the study was conducted in the United States, that would be anyone who is not a run-of-the-mill Protestant.

Arguably, there is a long leap of logic in all these articles in saying that hippocampal atrophy is related to religious affiliation and I would argue there are three main reasons for this;

1)  Correlation ≠ causation. This one has become a bit of a mantra, but you can never say ‘correlation does not equal causation’ too much. The fact that born-again Protestants have smaller hippocampi does not automatically mean that being religious causes brain atrophy.

2)  Generalisation. Looking at religious behaviour and self-reported faith confessions is a very complex task. While we may see the commonalities among, say, Catholic groups across nations, it is also easy to see how two congregations of the same denomations may differ greatly in their ideas, experience and self-image. Being a Protestant in Illinois is certainly not the same as being a Protestant in Namibia.

3)  Complexity. Religiosity is a large number of behaviours and cognitive patterns that affects many facets of an individual’s life. To reduce all this to societal stress seems severly reductionist and ignores the vast complexity of behaviour and thought that is religious life. Arguably stress may play a significant role, but it is by no means the only aspect of religiosity which may be linked to physical changes in the brain.

With this, I would argue that it is a gross over-simplification to say that “Religious experiences shrink part of the brain”. We have to accept that the complex methodological framework is going to be lost in translation into popular media and all the more reason to emphasize what this study does not show (if you are in doubt, go to the MedicalXpress comments section). It does not show that being religious shrinks your brain. It does not show that being a born-again Christian makes you stupid. And it certainly does not show that religiosity leads to ‘brain damage’, as some keen readers are quick to point out.

What it does show, is that exciting science does take place at the core of controversial issues, that we need to incorporate discussions about method, generalisation and complexity and that we need to talk about what results mean and do not mean in our popularisation of current science.


Original paper at PLoS ONE.