Figure 3.

Histograms of parameter estimates (effect size) for non-parametrically modulated activity in regions of group-level difference, displayed in Figure. 2, but for a sub-set analysis of the 25 most neutral and 25 most positive images. To determine whether increases in activation observed in the sleep-deprivation group were due to a generalized (non-specific) amplified reactivity to all stimulus kinds, independent of emotion strength, a further subset analysis of the upper quartile stimulus set (most positive) and lower quartile stimulus set (most neutral) was performed for regions identified as different between both groups. (A) For all regions describe as more reactivity in the deprivation group (Figure 2A), the sub-set analyses revealed similar activation levels between both groups in response to the most neutral pictures, yet highly significant differences between groups for the most positive pictures. Between-group statistical t-test comparisons are provided within figure. All within group comparisons between the most neutral and most positive stimuli were significant in the deprivation group (all P < 0.04), yet non-significant in the control group (all P > 0.12), with the exception of activity in the right amygdala, which showed a trend towards significance (P = 0.07). Therefore, across all regions showing greater reactivity in the deprivation group across the entire stimulus set, a condition-specific relationship was observed, expressly in response to positive stimuli, while reactivity to more neutral images was similar in both groups. (B) This was also true for the reduction in activity identified in the parahippocampus and left occipital gyrus in the deprivation group. However, it was not the case for the remaining region showing decreased reactivity at the overall group level in the sleep-deprived participants—the precuneus—which demonstrated non-specific reductions in reactivity for both neutral and negative stimulus sub-sets, relative to the control group. Between-group statistical t-test comparisons are provided within figure. All within group comparisons between the most neutral and most positive stimuli were significant in the control group and deprivation group (all P < 0.03), with the exception of activity in the precuneus in the control group (P = 0.56). All between group comparisons reflect significance (P) at: * < 0.05 and ** < 0.005. Error bars represent standard error.