Sodium Oxybate Alters Sleep Architecture and Reduces Emotional Selectivity in Memory-Related Responses

Sleep supports memory consolidation. Non-rapid eye movement (NREM) and rapid eye movement (REM) sleep have been proposed to support, respectively, declarative memory consolidation and the integration of the memory affective dimension. Here, we used sodium oxybate (SXB) to modify the NREM/REM proportion during one sleep night and assessed subsequent emotional memory retrieval and related neurophysiological underpinnings. In a double-blind, randomized, cross-over study, 19 healthy young men spent two monitored nights (SXB/placebo). Before sleep, participants encoded emotional and neutral pictures, followed by a recognition test the following afternoon during fMRI scanning. We hypothesized that modifying NREM/REM sleep balance would alter memory consolidation across behavioural, neural and physiological levels, leading to a desensitization to emotional stimuli. SXB increased NREM (percentage, delta power) and reduced REM sleep (percentage, theta power), without affecting sleep efficiency. Memory performance did not differ between conditions. However, autonomic responses were altered: pupil diameter increased selectively for neutral pictures after the SXB night. We demonstrated that this reduced emotion selectivity was associated with the SXB effect on REM sleep, with smaller REM reductions yielding larger differential pupillary responses. At the brain level, fMRI analyses indicated stronger responses in the amygdala, hippocampus, locus coeruleus and orbitofrontal cortex to emotional versus neutral stimuli after placebo, but not after the SXB night. Orbitofrontal responses correlated with REM sleep only in the placebo condition. No significant associations were found with NREM enhancement. Overall, these findings indicate that the NREM/REM balance and probably REM sleep, plays an important role in maintaining emotional selectivity during memory consolidation.