It is known that sleep deprivation leads to exaggerated neural and behavioral reactivity to negative, aversive experiences, but some patients with depression seem to perk up with lack of sleep. Gujar et al. now find that sleep deprivation also increases the reactivity of our brain reward networks, biasing us towards more positive appraisals of good emotional experiences. They did MRI measurements on 14 people who hadn't slept for about 36 hours while presenting them with emotionally neutral and pleasant-looking images. The volunteers rated a greater proportion of the images as 'pleasant' than did people who had maintained a normal sleep routine.:
....Using functional magnetic resonance imaging (fMRI), .. we demonstrate that sleep deprivation amplifies reactivity throughout human mesolimbic reward brain networks in response to pleasure-evoking stimuli. In addition, this amplified reactivity was associated with enhanced connectivity in early primary visual processing pathways and extended limbic regions, yet with a reduction in coupling with medial frontal and orbitofrontal regions. These neural changes were accompanied by a biased increase in the number of emotional stimuli judged as pleasant in the sleep-deprived group, the extent of which exclusively correlated with activity in mesolimbic regions. Together, these data support a view that sleep deprivation not only is associated with enhanced reactivity toward negative stimuli, but imposes a bidirectional nature of affective imbalance, associated with amplified reward-relevant reactivity toward pleasure-evoking stimuli also. Such findings may offer a neural foundation on which to consider interactions between sleep loss and emotional reactivity in a variety of clinical mood disorders.