Short term memory depends largely on the prefrontal cortex. Yet, according to the model proposed by Etienne Koechlin, Director of the Cognitive Sciences Laboratory at the École Normale Supérieure (Paris), this cortex is arranged in a hierarchy consisting of four components. The first, ‘sensorial control’ has the task of responding to stimuli; it is secured by the premotor cortex, in the furthest back position of the prefrontal cortex. Placed in a position a little more forward, the prefrontal posterior cortex has the task of ‘contextual control’ assigned to it. It is it which permits the carrying out of tasks such as pushing button A on the appearance of a blue cross and button B when a green cross appears. The ‘episodic control,’ for its part, takes into account the whole history of stimuli during the carrying out of a task in order to provide the response which is the best adapted to the present moment. It enlists a region more anterior than the prefrontal cortex. Finally, at the peak of the hierarchy is situated the ‘executive control’ on which are based notably our strategic decisions. It is underpinned by the most polar region of the prefrontal cortex.

The region of the frontal cortex whose activity is maintained in the 4/4 subjects, whilst it is reduced under the effects of sleep pressure in 5/5 individuals, sits in the right prefrontal posterior region, a zone assigned to ‘contextual control.’ The compensatory region recruited by 4/4 individuals after sleep deprivation corresponds to the prefrontal cortex allocated to ‘episodic control.’ ‘What do the individuals who have the PER3 4/4 genotype do to prevent a dip in their performance linked to sleep deprivation? They enlist notably the hierarchically superior regions of the prefrontal cortex, which gives them access to more flexible and adaptive action strategies,’ explains Pierre Maquet.