Sleep plays a key role in attention, vigilance, memory consolidation but also emotion regulation. Emotion is a collection of behaviors that allows to prioritize important information. Emotion affects a large part of cognition including memory.
In the introduction, we will summarize the main experiences demonstrating that the emotional memory traces is spontaneously replayed during sleep to enhance subsequent retention. Next, we will demonstrate that sleep loss alters the regulation of emotion and enhances stress level. Finally, we will demonstrate the link between mood disorders and sleep disturbances. Data on adults but also adolescents will be described, because this population is at a key period of development with major changes in sleep physiology, large modification of emotion reaction, and deep reorganization of brain maturation.
The aim of this thesis it to report scientific data showing the strong link between sleep, emotion and memory. The set of studies that I present attempts to understand what functional mechanisms take place during wakefulness and sleep and which brain regions play a role in emotion regulation and emotional memory. We used advanced neuroscience brain imaging techniques, including functional MRI, surface EEG and intracranial EEG in human to unravel the brain correlates at wake and during sleep.
In the first study, using fMRI, we reactivated an emotional memory trace during REM sleep with auditory cues and we observed an enhancement of the cortical responses related to these memories during subsequent retrieval. In the second study, we also reactivated emotional memory using auditory cues during a nap. Brain response was measured by intracranial electrodes implanted in epileptic patients. We showed that specific oscillations (slow oscillations and spindles) trigger the reactivation of the emotional memory trace during REM sleep particularly in the orbitofrontal cortex. In the third study, healthy participants were invited to sleep in the MRI after playing two different games that lead to a reward or not. Using a decoding approach, we observed that the rewarded game was preferentially reactivated during NREM sleep. More the game was reactivated, better were the memory performances on the next day. On the fourth study, we demonstrated that the amount of stressful dreams predict the ability to regulate emotion at wake using fMRI.
Finally, the main message of this thesis is that we need to take care of our sleep because it is much more important for our emotions and moods than we may think. Public health measures are needed to raise awareness of the importance of sleep, especially among adolescents.
