Sleep loss and night-time impair the recognition of emotional facial expressions but not the perception of emotional verbal stimuli

Recently, it has been observed an amplified hyper-limbic response by the human amygdala to negative emotional stimuli and amplified human mesolimbic reward brain networks in response to pleasure-evoking stimuli under conditions of Sleep Deprivation (SD). Furthermore SD selectively impairs the subjective judgment of human facial emotions. This study aims to evaluate the effect of partial SD and nighttime on the recognition of emotional faces (EF) and words (EW). Eighteen healthy volunteers (3M/15F; mean age: 24.3 ± 2.3) had to discriminate the emotional valence (negative NG, positive PS, neutral NU) of the stimuli (EF, EW) presented laterally to a central fixation by pressing a key on the clipboard. The experiments were run on two consecutive days. In the morning of the first day, participants performed the training task. On the second day, after participants slept their usual 8 h, they were kept awake for 24 h and were required to perform the EF test at about 12.00a.m. (Baseline: BSL) and at 3.00 am. (SD) and the EW test at about 6.00 p.m. (BSL) and at 7.00a.m. (SD). The order of BSL and SD conditions were balanced across subjects. Results showed that the emotional valence modules the SD effect only during the face recognition, while emotional valence does not interact with SD effect when EW are used. These findings suggest that SD affects the processing of emotional stimuli only when the latter have an important biological value (e.g. they are faces).