Aberrant Parasympathetic Stress Responsivity in Pure and Co-Occurring Major Depressive Disorder and Generalized Anxiety Disorder.

Major Depressive Disorder (MDD) and Generalized Anxiety Disorder (GAD) are highly comorbid; we know little, however, about the shared physiological features of these disorders. In the present study, we examined whether aberrant parasympathetic stress responsivity represents a transdiagnostic process in MDD, GAD, and co-occurring MDD-GAD. Adult women diagnosed with MDD only, GAD only, and co-occurring MDD-GAD and never-disordered controls (CTLs) completed a standardized laboratory task that involved anticipating, confronting, and recovering from a social stressor. Participants' levels of respiratory sinus arrhythmia (RSA) were measured to index para-sympathetic responses. The three clinical groups combined (participants with MDD only, GAD only, and co-occurring MDD-GAD) exhibited a similar pattern of RSA responsivity that differed significantly from that of the CTL group. Specifically, whereas CTL participants exhibited a sharp decrease in RSA when confronting the stressor and a sharp increase in RSA when recovering immediately following the stressor, the clinical participants exhibited a blunted response pattern that involved weaker fluctuations in RSA when confronting and recovering from the stressor. There were no significant differences among the three clinical groups in RSA responses. Interestingly, clinical and CTL participants did not differ in self-reported fluctuations in negative emotional arousal. Finally, for clinical participants patterns of RSA reactivity to the acute stressor were associated differentially with trait rumination and worry as maladaptive forms of emotion regulation. These findings support the formulation that aberrant parasympathetic stress responsivity is a shared feature of MDD, GAD, and co-occurring MDD-GAD that is characterized by diminished reactivity to and recovery from stress.