Transcranial Direct Current Stimulation Over the Prefrontal Cortex in Depression Modulates Cortical Excitability in Emotion Regulation Regions as Measured by Concurrent Functional Magnetic Resonance Imaging: An Exploratory Study.

BACKGROUND: A well-established impaired top-down network for effortful emotion regulation (ER) in major depressive disorder (MDD) includes the dorsal and ventromedial prefrontal cortex (PFC) and the amygdala. Transcranial direct current stimulation (tDCS) is a noninvasive neuromodulation method that has been used successfully to induce mood changes in MDD. Despite reliable findings, little is known regarding the precise effects of tDCS on cortical excitability in vivo in depression and how such changes relate to ER. Here, we addressed this question by combining-for the first time in a psychiatric sample-tDCS with functional magnetic resonance imaging in a single-blind randomized design. METHODS: We applied anodal tDCS over the left PFC (area F3 per the 10/20 system) together with cathodal tDCS over the right PFC (F4) or sham tDCS during functional magnetic resonance imaging in patients with moderate to severe MDD (n = 20) and gender- and age-matched control subjects (n = 20). Participants performed 2 runs of an ER task prior to tDCS and 2 runs of the task during tDCS, which was administered at 1.5 mA with 5-cm × 5-cm electrodes. RESULTS: Whole-brain, region of interest, and connectivity analyses revealed an impaired ER network in patients with MDD prior to stimulation. Active anodal tDCS over the left (with concurrent cathodal stimulation of the right) PFC during reappraisal of negative stimuli upregulated activity in ventromedial PFC, which was predictive of gains in reappraisal performance during stimulation for the patients with MDD. CONCLUSIONS: The results of this study offer insights into the mechanisms of action of tDCS and support its potential as a treatment for depression.

The depressogenic potential of added dietary sugars.

Added sugars are ubiquitous in contemporary Western diets. Although excessive sugar consumption is now robustly associated with an array of adverse health consequences, comparatively little research has thus far addressed its impact on the risk of mental illness. But ample evidence suggests that high-dose sugar intake can perturb numerous metabolic, inflammatory, and neurobiological processes. Many such effects are of particular relevance to the onset and maintenance of depressive illness, among them: systemic inflammation, gut microbiota disruption, perturbed dopaminergic reward signaling, insulin resistance, oxidative stress, and the generation of toxic advanced glycation end-products (AGEs). Accordingly, we hypothesize that added dietary sugars carry the potential to increase vulnerability to major depressive disorder, particularly at high levels of consumption. The present paper: (a) summarizes the existing experimental and epidemiological research regarding sugar consumption and depression vulnerability; (b) examines the impact of sugar ingestion on known depressogenic physiological processes; and (c) outlines the clinical and theoretical implications of the apparent sugar-depression link. We conclude that the extant literature supports the hypothesized depressogenic impact of added dietary sugars, and propose that an improved understanding of the effects of sugar on body and mind may aid in the development of novel therapeutic and preventative measures for depression.

Effects of incidental positive emotion and cognitive reappraisal on affective responses to negative stimuli.

Previous studies have identified two powerful ways to regulate emotional responses to a stressor: experiencing incidental positive emotions and using cognitive reappraisal to reframe the stressor. Several cognitive and motivational theories of positive emotion support the formulation that incidental positive emotions may facilitate cognitive reappraisal. To test the separate and interacting effects of positive emotions and cognitive reappraisal, we first adapted an established picture-based reappraisal paradigm by interspersing blocks of positive emotion inducing and neutral pictures. Across two pre-registered studies (Studies 1, 2), reappraisal effectively decreased self-reported negative emotions and increased self-reported positive emotions; however, experiencing incidental positive emotions did not facilitate reappraisal success. In another preregistered study (Study 3), we employed a more powerful positive emotion induction via virtual reality (VR), used a social stress anticipation task, and instructed participants to reappraise the anticipated stressor positively. Although there was a robust effect of the positive emotion induction (relative to the neutral induction) on feeling more positive emotions throughout stress anticipation, the results again indicated that incidental positive emotions did not facilitate cognitive reappraisal. We propose that incidental positive emotions and cognitive reappraisal may constitute separate pathways of influence when regulating one's responses to negative events.

The Neurodynamics of Affect in the Laboratory Predicts Persistence of Real-World Emotional Responses.

Failure to sustain positive affect over time is a hallmark of depression and other psychopathologies, but the mechanisms supporting the ability to sustain positive emotional responses are poorly understood. Here, we investigated the neural correlates associated with the persistence of positive affect in the real world by conducting two experiments in humans: an fMRI task of reward responses and an experience-sampling task measuring emotional responses to a reward obtained in the field. The magnitude of DLPFC engagement to rewards administered in the laboratory predicted reactivity of real-world positive emotion following a reward administered in the field. Sustained ventral striatum engagement in the laboratory positively predicted the duration of real-world positive emotional responses. These results suggest that common pathways are associated with the unfolding of neural processes over seconds and with the dynamics of emotions experienced over minutes. Examining such dynamics may facilitate a better understanding of the brain-behavior associations underlying emotion. Significance statement: How real-world emotion, experienced over seconds, minutes, and hours, is instantiated in the brain over the course of milliseconds and seconds is unknown. We combined a novel, real-world experience-sampling task with fMRI to examine how individual differences in real-world emotion, experienced over minutes and hours, is subserved by affective neurodynamics of brain activity over the course of seconds. When winning money in the real world, individuals sustaining positive emotion the longest were those with the most prolonged ventral striatal activity. These results suggest that common pathways are associated with the unfolding of neural processes over seconds and with the dynamics of emotions experienced over minutes. Examining such dynamics may facilitate a better understanding of the brain-behavior associations underlying emotion.