Abstract
According to the emotion-context insensitivity (ECI) hypothesis, major depressive disorder (MDD) is associated with a diminished ability to react emotionally to positive stimuli and with blunting of defensive responses to threat. That defensive responses are blunted in MDD seems inconsistent with the conceptualization and diagnostic nosology of MDD. The present study tested the ECI hypothesis in MDD using a threat of shock paradigm. Twenty-eight patients with MDD (35.5±10.4 years) were compared with 28 controls (35.1±7.4 years). Participants were exposed to three conditions: no shock, predictable shock, and unpredictable shock. Startle magnitude was used to assess defensive responses. Inconsistent with the ECI hypothesis, startle potentiation to predictable and unpredictable shock was not reduced in the MDD group. Rather, MDD patients showed elevated startle throughout testing as well as increased contextual anxiety during the placement of the shock electrodes and in the predictable condition. A regression analysis indicated that illness duration and Beck depression inventory scores explained 37% (p<.005) of the variance in patients’ startle reactivity. MDD is not associated with emotional blunting but rather enhanced defensive reactivity during anticipation of harm. These results do not support a strong version of the ECI hypothesis. Understanding the nature of stimuli or situations that lead to blunted or enhanced defensive reactivity will provide better insight into dysfunctional emotional experience in MDD.
Highlights
Major depressive disorder (MDD) is a devastating psychiatric condition of mood dysregulation characterized by disturbance in positive and negative emotional experiences
Startle Given that previous studies have reported either normal or reduced startle responses in startle reactivity in MDD, we reasoned that if the MDD patients were sensitive to contextual anxiety, this would be reflected as an overall elevated startle reactivity during the habituation procedures and/or during the subsequent NPU threat test
Consistent with our hypothesis, there was no evidence of blunted startle potentiation in the MDD group; anticipation of shocks led to a robust level of startle potentiation in the MDD patients
Summary
Major depressive disorder (MDD) is a devastating psychiatric condition of mood dysregulation characterized by disturbance in positive and negative emotional experiences. The ECI hypothesis has recently been supported in a meta-analysis [6], the hypothesis that MDD shows reduced defensive response is inconsistent with substantial neurocognitive evidence of hyperactive aversive emotional responding [7,8] and with the theoretical conceptualization that depression and anxiety disorders share a common distress factor of heightened affective negativity [9]. Such a distress factor leads to an alternative to the ECI hypothesis, the negative potentiation hypothesis [6], which predicts exaggerated not blunted response to aversive stimuli. High trait anxiety/neuroticism is a vulnerability marker for depression [13] and depressed individuals exhibit substantially high levels of anxiety/neuroticism, which should lead to exaggerated aversive responding
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