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Review of "Circadian Preference Modulates the Neural Substrate of Conflict Processing across the Day"

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Are you a morning lark, or a night owl?  This could impact your cognitive and neural performance.

This study by Schmidt et al., is an extension of work by the same group first published in Science  in 2009.

So, first to briefly review the original Science paper; the authors, tested people who were morning and evening types (according to chronotype questionnaires, melatonin levels and polysomnography) at optimal and non-optimal times (i.e. synchronous and asynchronous times relative to chronotype).  They found that fast responses on a psychomotor vigilance task, (indicating greater vigilance) was associated with more BOLD activity at synchrony. The effects were observed in Locus Coeruleus and anterior hypothalamus (the location of the suprachiasmatic nucleus or "master clock" of the body), and provided initial evidence for observable time of day effects measured with fMRI.

Well and good - and actually very impressive being one of the seminal fMRI studies in this area.


The current study by the same group and using the same participants builds on the previous findings by asking whether these same effects can be found in more cognitively complex tasks.

Participants were scanned either 1.5 or 10.5 hours after they woke up, so that it was early or late according to their chronotype (morning types might get up at 6:30 and be scanned at 8:00, whereas evening types could roll out of bed at 10:30 and be scanned at noon).  Those with poor sleep habits (as determined by polysomnography) were discarded and the rest were tested in both morning and evening sessions according to a counterbalance).

The complex task the authors used was the Stroop task in order to look at putatively inhibatory regions (there might be a few problems with this task choice, but more on that later).  In terms of behavioural measures, the authors did not find the expected differences in chronotype or time of testing - perhaps since classically the Stroop requires people to vocalize their responses before pushing a button - whereas this would not be possible in an fMRI scan since excess motion could falsely register as signal.

So, no behavioural differences; this makes interpreting the meaning of BOLD signal changes a bit more challenging, but the authors have argued that this lack of difference means that the brain difference was not driven by differences in performance.  No argument there.  Ideally though, one would want a task or condition where both groups performed similarly and another where they differed.

On to the BOLD differences.  The authors report BOLD differences for the interaction between chronotype and time of testing on the interference condition (see below).
The effect shows up in areas typically involved in error processing (insula) and attention regulation (parietal regions) so that morning types activate these areas more in the morning and evening types activate them in the evening which fits nicely with their hypothesis. The question remains though, without a behavioural difference, what does this mean?  Perhaps if the authors had examined the fastest and slowest responses they could have uncovered a reaction time difference - this would be in line with arguments from the ex-Gaussian literature where proponents argue that the slowest RTs often reveal a group effect even if the mean does not.  That said, the effect is still very interesting, and agrees with work from other groups including work done by Vandewalle and colleagues exploring the genetics of chronotype (i.e. Vandewalle et al., 2009).  

The authors then regressed interference related responses during the evening session on SWA spectral power values (acquired from the polysomnography recordings) and used this to predict brain activity using whole brain analysis.  The authors report an interaction in a posterior hypothalamic region that is involved in arousal.   I understand the need to show a difference in hypothalamic regions associated with sleep and arousal, but found the analysis to be a bit convoluted - why not just use a seed in the hypothalamus and see whether that is modulated by chronotype and time of testing?

Regardless,  this study is on the whole certainly worth reading as it is well written and is one of the first fMRI studies examining the effects of chronotype and time of testing on complex cognitive tasks.


Schmidt, C., Collette, F., Leclercq, Y., Sterpenich, V., Vandewalle, G., Berthomier, P., Berthomier, C., et al. (2009). Homeostatic sleep pressure and responses to sustained attention in the suprachiasmatic area. Science (New York, N.Y.), 324(5926), 516-9. doi:10.1126/science.1167337

Schmidt, C., Peigneux, P., Leclercq, Y., Sterpenich, V., Vandewalle, G., Phillips, C., Berthomier, P., et al. (2012). Circadian preference modulates the neural substrate of conflict processing across the day. PloS one, 7(1), e29658. doi:10.1371/journal.pone.0029658
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0029658

Vandewalle, G., Archer, S. N., Wuillaume, C., Balteau, E., Degueldre, C., Luxen, A., Maquet, P., et al. (2009). Functional magnetic resonance imaging-assessed brain responses during an executive task depend on interaction of sleep homeostasis, circadian phase, and PER3 genotype. The Journal of neuroscience : the official journal of the Society for Neuroscience, 29(25), 7948-56. doi:10.1523/JNEUROSCI.0229-09.2009
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