Late evening brain activation patterns and their relation to the internal biological time, melatonin, and homeostatic sleep debt

Abstract

Sleep propensity increases sharply at night. Some evidence implicates the pineal hormone melatonin in this process. Using functional magnetic resonance imaging, brain activation during a visual search task was examined at 22:00 h (when endogenous melatonin levels normally increase). The relationships between brain activation, endogenous melatonin (measured in saliva), and self-reported fatigue were assessed. Finally, the effects of exogenous melatonin administered at 22:00 h were studied in a double blind, placebo-controlled crossover manner. We show that brain activation patterns as well as the response to exogenous melatonin significantly differ at night from those seen in afternoon hours. Thus, activation in the rostro-medial and lateral aspects of the occipital cortex and the thalamus diminished at 22:00 h. Activation in the right parietal cortex increased at night and correlated with individual fatigue levels, whereas exogenous melatonin given at 22:00 h reduced activation in this area. The right dorsolateral prefrontal cortex, an area considered to reflect homeostatic sleep debt, demonstrated increased activation at 22:00 h. Surprisingly, this increase correlated with endogenous melatonin. These results demonstrate and partially differentiate circadian effects (whether mediated by melatonin or not) and homeostatic sleep debt modulation of human brain activity associated with everyday fatigue at night. Hum Brain

Residual effects of emotion are reflected in enhanced visual activity after sleep

“…Prior work has shown evidence of increased occipital activity in response to visual stimuli in the morning relative to evening (Gorfine & Zisapel, 2009), which would be consistent with our finding that the sleep group, who tested in the morning, showed heightened occipital activity during the retrieval of negative contexts relative to the wake group, who tested in the evening. Importantly, however, this was not the case when comparing the morning short delay and evening short delay groups in the present study.…”

Stress hormones, sleep deprivation and cognition in older adults

“…In this way, melatonin serves as a signal of darkness in the organism, affecting the brain structures associated with the circadian cycles [115]. Melatonin receptors (MT1 and MT2) have been detected in the suprachiasmatic nucleus of the hypothalamus and are believed to be involved in the regulation of the sleep-wake cycle [116].…”

New perspectives on the role of melatonin in human sleep, circadian rhythms and their regulation

“…In addition, melatonin acts at the default mode network (DMN) regions in the brain to promote fatigue and sleep‐like changes in activation of the precuneus (Gorfine et al, 2006; Gorfine and Zisapel, 2009). The DMN is a network of brain regions that is active during rest in the absence of task‐dependent performance (Raichle et al, 2001).…”

“…The fMRI‐assessed visual search task related activation of brain networks (adapted from Gorfine et al, 2006; Gorfine and Zisapel, 2009). (A) The effect of exogenous melatonin administration at 16:00 h on task‐related activity.…”