- It confirms the obvious fact that people with different sleep rhythms have different white matter properties.
- It fails to do much more.
Before looking critically at the paper, I will say that I agree with many of the conclusions it comes to. for instance that society's clock driven culture leaving people in chronic jet-lag states which drain them, and that flexible working hours would help those people (and the transport network).
I'm writing about it because it demonstrates an example of how many MRI neuroimaging studies are flawed.
The authors relate chronotype (early bird or night owl) to brain changes, and also to use of recreational drugs (alcohol and nicotine).
Now anybody can see that people who might stay up late may be using stimulants or hedonistic substances. However in this paper they use a crude test to 'control' for this effect, by looking for a Pearson correlation coefficient between each MRI variable and each social measure (alcohol, nicotine etc). Why is this flawed?
1. Self reported consumption levels are inaccurate
2. consumption does not linearly relate to the effect on that person
3. many other substances were not included, such as chocolate, refined sugar, cannabis
4. there was no reference values for the correlation coefficient. this would probably need to be defined in a separate study, properly powered for the purpose.
This paper is the tip of the iceberg of similar studies which have the basic formula;
Take small sample of healthy males. Do MRI scans. Relate scans to some ill-defined phenomena in lay-psychology, such as 'niceness' or 'funny'. Had this study clearly defined chronotype, and dissected it out from the numerous confounding factors, it might have been of more value.
Ideally the study would have had matched pairs, or have used genuinely jet lagged people, to add relevant comparison.
“Early to bed, early to rise”: Diffusion tensor imaging identifies chronotype-specificity
Jessica Rosenberga et al
NeuroImage 2013
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