0331 Neurological Impact on the Reward Processing of Food Images Imposed by Mild Sleep Restriction in Adolescents

Introduction

Previous studies indicate that lack of sleep might increase risk for unhealthy eating and obesity. This is particularly important during adolescence, when most youth sleep less than the recommended 8-10 hours/night and dietary habits are developed that extend into adulthood. This study investigated the relationship between multi-night sleep restriction and the appeal of food, including neuroimaging to examine the impact on brain responses to food-related stimuli.

Methods

Healthy 14-17 year-old adolescents (n=39) completed an experimental sleep manipulation across consecutive five-night periods to compare nightly sleep of approximately 9 hours (healthy sleep duration) vs. about 6.3 hours (mild sleep restriction). At the end of each week, participants underwent functional MRI while performing a visual food appeal task. The task included 42 photos in each of four food categories (sweets, snacks, fast-food, meat/fruit/vegetable) and one non-food category. Photos were presented every 3 seconds in blocks of 7 within each category; 6 interleaved blocks per category. Teens rated the appeal of each block of photos. General linear modeling explained regional brain response according to categorical presentation time-courses.

Results

The pattern of brain responses to the different food types was similar across the two sleep conditions. However, the sleep manipulation led to significant regional effects when contrasting the totality of food vs non-food images. Specifically, when compared to non-food, food images overall resulted in greater activation in the ventral tegmental area (VTA) and substantia nigra (SN) during sleep restriction. Both regions have been previously shown to be involved in processing reward-related information.

Conclusion

Our findings suggest neuronal responses in reward circuitry for teens viewing food images are influenced by sleep duration. Sleep restriction may affect reward processing of food in teens by increasing brain activation in VTA/SN network components that underlie dopamine-mediated motivational drive.

Support

Supported by NIH R01HL120879

Comparison of SNR and CNR for in vivo mouse brain imaging at 3 and 7 T using well matched scanner configurations

Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) for magnetic resonance microimaging were measured using two nearly identical magnetic resonance imaging (MRI) scanners operating at field strengths of 3 and 7 T. Six mice were scanned using two imaging protocols commonly applied for in vivo imaging of small animal brain: RARE and FLASH. An accounting was made of the field dependence of relaxation times as well as a small number of hardware disparities between scanner systems. Standard methods for relaxometry were utilized to measure T1 and T2 for two white matter (WM) and two gray matter (GM) regions in the mouse brain. An average increase in T1 between 3 and 7 T of 28% was observed in the brain. T2 was found to decrease by 27% at 7 T in agreement with theoretical models. The SNR was found to be uniform throughout the mouse brain, increasing at higher field by a factor statistically indistinguishable from the ratio of Larmor frequencies when imaging with either method. The CNR between GM and WM structures was found to adhere to the expected field dependence for the RARE imaging sequence. Improvement in the CNR for the FLASH imaging sequence between 3 and 7 T was observed to be greater than the Larmor ratio, reflecting a greater susceptibility to partial volume effects at the lower SNR values at 3 T. Imaging at 7 T versus 3 T in small animals clearly provides advantages with respect to the CNR, even beyond the Larmor ratio, especially in lower SNR regimes. This careful multifaceted assessment of the benefits of higher static field is instructive for those newly embarking on small animal imaging. Currently the number of 7 T MRI scanners in use for research in human subjects is increasing at a rapid pace with approximately 30 systems deployed worldwide in 2008. The data presented in this article verify that if system performance and radio frequency uniformity is optimized at 7 T, it should be possible to realize the expected improvements in the CNR and SNR compared with MRI at 3 T.