As for the conflict management test, which was based on the use of the Stroop test (it was a question of inhibiting an automatic response in favour of a more controlled procedure), it delivered a strange truth: the performances of the ‘extreme morning types’ are equivalent to those of the ‘extreme evening types’, but the activity of certain areas of the brain involved in conflict management (insula, anterior cingulate cortex) increased with the waking time of the latter, and uniquely for them. Why? The researchers will make every effort to pierce this mystery. ‘If we had carried out the test 16 hours after waking up, for example, it is possible that the performances of the ‘evening subjects’ would have turned out to be superior to those of the ‘morning subjects,’ stresses Christina Schmidt. ‘From this we can imagine that the differences of activation within the brain would be reflected in the level of performances, as if after going up a level.’ As far as the suprachiasmatic nucleus and the locus coeruleus are concerned, the results confirm the data of the visual attention test, but with a lower statistical threshold.

Neuro-psychological evaluations

The work initiated at the University of Liège do not spring solely from the sphere of basic research, but also have the ambition to influence clinical practices. In effect, the neuro-psychological evaluations today carried out to explore the cognitive functioning of brain damaged patients generally tend not to take into account the existing links between the time of day the tests are carried out and the individual chronotype of the subject being examined.

Let us say that we want to follow up a patient over the long term in evaluating his cognitive performances every three months. If the tests take place sometimes in the beginning of the morning, sometimes at midday, sometimes at the end of the afternoon, for example, the measurements of the case’s development could be distorted. The same could be the case if, putting to one side the time of day, we submitted a person to a single test in order to analyse his results in the light of those of a control group. In addition, young and old subjects are placed on the same footing, whereas we know that the more we age, the more we swing towards a morning chronotype. ‘In certain tests, it has been shown that the differences in performance between these two types of people were erased when the young individuals were tested at a non-optimal moment and the elderly individuals were tested at the moment of their circadian peak,’ stresses Christina Schmidt on the other hand.