Recovery from Unrecognized Sleep Loss Accumulated in Daily Life Improved Mood Regulation via Prefrontal Suppression of Amygdala Activity

Many modern people suffer from sleep debt that has accumulated in everyday life but is not subjectively noticed [potential sleep debt (PSD)]. Our hypothesis for this study was that resolution of PSD through sleep extension optimizes mood regulation by altering the functional connectivity between the amygdala and prefrontal cortex. Fifteen healthy male participants underwent an experiment consisting of a baseline (BL) evaluation followed by two successive interventions, namely, a 9-day sleep extension followed by one night of total sleep deprivation (TSD). Tests performed before and after the interventions included a questionnaire on negative mood and neuroimaging with arterial spin labeling MRI for evaluating regional cerebral blood flow (rCBF) and functional connectivity. Negative mood and amygdala rCBF were significantly reduced after sleep extension compared with BL. The amygdala had a significant negative functional connectivity with the medial prefrontal cortex (FCamg–MPFC), and this negative connectivity was greater after sleep extension than at BL. After TSD, these indices reverted to the same level as at BL. An additional path analysis with structural equation modeling showed that the FCamg–MPFC significantly explained the amygdala rCBF and that the amygdala rCBF significantly explained the negative mood. These findings suggest that the use of our sleep extension protocol normalized amygdala activity via negative amygdala–MPFC functional connectivity. The resolution of unnoticed PSD may improve mood by enhancing frontal suppression of hyperactivity in the amygdala caused by PSD accumulating in everyday life

Decreased activity in the reward network of chronic insomnia patients

In modern society, many people have insomnia. Chronic insomnia has been noted as a risk factor for depression. However, there are few functional imaging studies of the brain on affective functions in chronic insomnia. This study aimed to investigate brain activities induced by emotional stimuli in chronic insomnia patients. Fifteen patients with primary insomnia and 30 age and gender matched healthy controls participated in this study. Both groups were presented images of fearful, happy, and neutral expressions consciously and non-consciously while undergoing MRI to compare the activity in regions of the brain responsible for emotions. Conscious presentation of the Happy-Neutral contrast showed significantly lower activation in the right orbitofrontal cortex of patients compared to healthy controls. The Happy-Neutral contrast presented in a non-conscious manner resulted in significantly lower activation of the ventral striatum, right insula, putamen, orbitofrontal cortex and ventral tegmental area in patients compared to healthy controls. Our findings revealed that responsiveness to positive emotional stimuli were decreased in insomniac patients. Specifically, brain networks associated with rewards and processing positive emotions showed decreased responsiveness to happy emotions especially for non-conscious image. The magnitude of activity in these areas also correlated with severity of insomnia, even after controlling for depression scale scores. These findings suggest that insomnia induces an affective functional disorder through an underlying mechanism of decreased sensitivity in the regions of the brain responsible for emotions and rewards to positive emotional stimuli

Neural Networks for Mindfulness and Emotion Suppression

<div><p>Mindfulness, an attentive non-judgmental focus on “here and now” experiences, has been incorporated into various cognitive behavioral therapy approaches and beneficial effects have been demonstrated. Recently, mindfulness has also been identified as a potentially effective emotion regulation strategy. On the other hand, emotion suppression, which refers to trying to avoid or escape from experiencing and being aware of one’s own emotions, has been identified as a potentially maladaptive strategy. Previous studies suggest that both strategies can decrease affective responses to emotional stimuli. They would, however, be expected to provide regulation through different top-down modulation systems. The present study was aimed at elucidating the different neural systems underlying emotion regulation via mindfulness and emotion suppression approaches. Twenty-one healthy participants used the two types of strategy in response to emotional visual stimuli while functional magnetic resonance imaging was conducted. Both strategies attenuated amygdala responses to emotional triggers, but the pathways to regulation differed across the two. A mindful approach appears to regulate amygdala functioning via functional connectivity from the medial prefrontal cortex, while suppression uses connectivity with other regions, including the dorsolateral prefrontal cortex. Thus, the two types of emotion regulation recruit different top-down modulation processes localized at prefrontal areas. These different pathways are discussed.</p></div

Coordinates of the brain areas activated in Observe-negative vs. Look-negative.

<p>Height threshold: <i>p</i> < .001 uncorrected, Extent threshold: <i>k</i> = 5 voxels. The x, y, and z coordinates by which a voxel is determined referring to medial–lateral (x: positive = right), anterior–posterior (y: positive = anterior), and superior–inferior (z: positive = superior) positions denote the peak location on the MNI template. T-scores denote the difference between the two sample means compared with the dispersion and sample sizes of the two samples. Z-scores are the numbers from the unit normal distribution that give the same p value as the t statistic. Abbreviations: BA = Brodmann area; MNI = Montreal Neurological Institute template.</p><p>Coordinates of the brain areas activated in Observe-negative vs. Look-negative.</p

VAS scores for negative affect after each coping strategy (bars represent standard errors).

<p>Significant differences were found for the comparisons of Look-neutral vs. other conditions and Look-negative vs. Suppress-negative, and Observe-negative. The two types of emotion regulation strategies were effective for regulation of subjective emotion.</p

Coordinates for the brain areas activated in Suppress-negative vs. Look-negative.

<p>Height threshold: <i>p</i> < .001 uncorrected, Extent threshold: <i>k</i> = 5 voxels. The x, y, and z coordinates by which a voxel is determined referring to medial–lateral (x: positive = right), anterior–posterior (y: positive = anterior), and superior–inferior (z: positive = superior) positions denote the peak location on the MNI template. T-scores denote the difference between the two sample means compared with the dispersion and sample sizes of the two samples.Z-scores are the numbers from the unit normal distribution that give the same p value as the t statistic. Abbreviations: BA = Brodmann area; MNI = Montreal Neurological Institute template.</p><p>Coordinates for the brain areas activated in Suppress-negative vs. Look-negative.</p

Neural activity for Suppress-negative (A) and Observe-negative (B) contrasted with Look-negative (<i>p</i> < .001 uncorrected).

<p>Regions with significantly greater activation in Suppress-negative compared to Look-negative condition included the left inferior frontal gyrus (IFG; BA47). During Observe-negative compared to Look-negative, there was greater activation in the precentral gyrus (BA6), IFG (BA44), superior frontal gyrus (SFG; BA6/8), middle temporal gyrus (MTG; BA21/22), inferior parietal lobule (IPL; BA40), putamen, and anterior insula (AI; BA13).</p

Correlation between regional AMG activity and functional connectivity to the AMG.

<p>The figures show brain regions that have more negative functional connectivity with the AMG when AMG responses were reduced during Suppress-negative (A) and Observe-negative (B) contrasted with Look-negative (<i>p</i> < .001 uncorrected).</p