Sleep : the architect of memory
The results of this test showed that when the "sleepers" recognized a picture and the encoding context, they called upon the hippocampo-cortical system (comprising the hippocampus, medial prefrontal cortex and the precuneus) significantly more than did the "non-sleepers", especially if the pictures had an emotional connotation. When remembering negative stimuli(1), the "non-sleepers" did not activate the hippocampus or the medial prefrontal cortex, but rather the amygdala, which is known to be involved in the evaluation of negative emotions, together with the visual areas. In other words, sleep-deprivation inhibited the hippocampo-cortical reactivations which the researchers suspected are active during sleep. However, as emotional stimuli likely enjoy significant adaptive status, an alternative, very primitive system that enables memories of this type to be consolidated, comes into play. Moreover, while the "sleepers", as expected, remembered neutral images better than the "non-sleepers", both groups' performance was similar as regards the images with an emotional connotation.
The intense activity recorded in the medial prefrontal cortex of the sleepers seventy-two hours after initial encoding suggests that the emotional connotation of a memory accelerates the consolidation process, and thereby the passing of the baton between the hippocampus and the cortex.
In conclusion, the memory of emotions seems to be intimately related to sleep, and the quality of this sleep the night following the perception of an emotional stimulus determines the specific processes of mnesic consolidation carried out by the brain.
(1) No significant results were recorded for the remembering of positive stimuli.