Partial sleep deprivation impacts impulsive action but not impulsive decision-making.

Sleep deprivation may lead to increased impulsivity, however, previous literature has focused on examining effects of total sleep deprivation (TSD) rather than the more common condition, partial sleep deprivation (PSD) or 'short sleep'. Moreover, it has been unclear whether PSD impacts impulse-related cognitive processes, and specifically if it differentially affects impulsive action versus impulsive decision-making. We sought to determine if short compared to long sleep (6 vs. 9h/night) impacts impulsive action via behavioral inhibition (Go/No-Go), and/or impulsive decision-making processes of risk taking (Balloon Analogue Risk Task [BART]) and preferences for immediate over delayed rewards (Delay Discounting). In a within-subject design, 34 participants (71% female, mean age=37.0years, SD=10.54) were assigned to four consecutive nights of 6h/night (short sleep) and 9h/night (long sleep) in their own home in random counterbalanced order. Sleep was measured via wrist-worn actigraphs to confirm adherence to the sleep schedules (mean short sleep=5.9h, SD=0.3; mean long sleep=8.6h, SD=0.3, p<0.001). The Go/No-Go, BART, and Delay Discounting tasks were completed following both sleep conditions. Participants had more inhibition errors on the Go/No-Go task after short (mean false alarms=19.79%, SD=14.51) versus long sleep (mean=15.97%, SD=9.51, p=0.039). This effect was strongest in participants reporting longer habitual time in bed (p=0.04). There were no differences in performance following long- versus short-sleep for either delay discounting or the BART (p's>0.4). Overall, these results indicate that four days of PSD diminishes behavioral inhibition abilities, but may not alter impulsive decision-making. These findings contribute to the emerging understanding of how partial sleep deprivation, currently an epidemic, impacts cognitive ability. Future research should continue to explore the connection between PSD and cognitive functions, and ways to minimize the occurrence and negative consequences of short sleep.

A pilot randomized controlled trial testing the effects of a routine-based intervention on outcomes in a behavioural weight loss programme.

BACKGROUND: Structured routines aimed at eating and sleep have been successfully employed in weight loss interventions for children. Although such routines are discussed in lifestyle modification programmes for adults, they are not a primary focus. PURPOSE: The purpose of this study is to determine if establishing healthy eating and sleep routines may improve outcomes in a behavioural weight loss (BWL) intervention. METHODS: Twenty-five overweight/obese participants (age = 52.4 ± 9.8; body mass index = 33.5 ± 4.1) were randomly assigned to either a 4-week routine-based intervention (ROU) targeting regular eating and sleep or an education control before beginning an 18-week BWL intervention. RESULTS: Routine-based intervention participants reported adhering to eating routines, with increased 'on-schedule' eating (p = 0.007) and decreased 'off-schedule' eating (p = 0.002) but showed no change in 'on-schedule' sleep (p = 0.74). However, contrary to our hypothesis, ROU participants lost less weight than controls after 6 weeks of BWL (2.3 ± 2.5 vs. 4.6 ± 2.6 kg, p = 0.04) and achieved only modest weight loss over the full 18 weeks (ROU: 3.2 ± 4.6 vs. education control: 5.8 ± 5.7 kg, p = 0.23). CONCLUSIONS: Focusing initially on establishing healthy sleep and eating routines led to poorer, rather than better, subsequent weight loss outcomes. Further studies using a longer initial intervention period or focusing on only sleep or eating behaviour are needed to determine whether establishing routines for eating and sleep behaviours can enhance weight loss in adults.

Human amygdala sensitivity to the pupil size of others.

Stimulation of the amygdala produces pupil dilation in animal and human subjects. The present study examined whether the amygdala is sensitive to variations in the pupil size of others. Male subjects underwent event-related functional magnetic resonance imaging while passively viewing unfamiliar female faces whose pupils were either unaltered (natural variations in large and small pupils) or altered to be larger or smaller than their original size. Results revealed that the right amygdala and left amygdala/substantia innominata were sensitive to the pupil size of others, exhibiting increased activity for faces with relatively large pupils. Upon debrief, no subject reported being aware that the pupils had been manipulated. These results suggest a function for the amygdala in the detection of changes in pupil size, an index of arousal and/or interest on the part of a conspecific, even in the absence of explicit knowledge.