The Impact of Acute Social Stress on Approach and Avoidance Motivation in Individuals with Depression: An Examination of Behavioural and Neurophysiological Indices of Motivation
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Stress is considered proximal to the maintenance of depression. However, precise mechanisms linking stress to depression maintenance are largely unknown. Depression is characterized by decreased motivation for, and response to, reward. Further, both exposure to stress and subjective response to stress have been shown to negatively affect several reward-related processes in healthy individuals. The goal of the current study was to examine the impact of acute stress exposure and response on behavioural approach and avoidance motivation, defined as willingness to expend effort for reward/to prevent loss, and frontal EEG alpha asymmetry, a neurophysiological index of motivation. Depressed (n= 57) and non-depressed (n= 44) participants were randomized to social exclusion versus inclusion on a Cyberball task. EEG was recorded in 2-minute blocks immediately before and following Cyberball. Following Cyberball, participants completed the Need Threat Scale (NTS), as a measure of response to social exclusion, and a modified version of the Effort Expenditure for Rewards Task (EEfRT) that included both reward and loss trials. Individuals with depression showed lower approach and avoidance motivation on the EEfRT than healthy comparisons. With regards to social stress exposure, individuals in the Cyberball exclusion condition showed higher avoidance motivation compared to individuals in the inclusion condition. There was no significant effect of stress exposure on approach motivation, nor significant interactions between stress exposure and diagnostic group for either approach or avoidance motivation. With regards to stress response, there was a significant interaction between stress response and diagnostic group for both approach and avoidance motivation. Specifically, lower NTS scores (i.e., greater threat to fundamental needs in response to Cyberball) predicted lower approach motivation and higher avoidance motivation but only for individuals with depression. With regards to frontal alpha EEG asymmetry, as predicted individuals with depression showed lower relative left frontal asymmetry compared to healthy comparisons when controlling for comorbid anxiety symptoms. Contrary to hypotheses, across groups, individuals in the exclusion condition showed greater post-stress relative left frontal asymmetry compared to those in the inclusion condition. These findings are discussed in light of previous literature and with regards to study strengths and considerations.