Time course of threat responding in panic disorder and depression.

Heightened sensitivity to threat is a characteristic feature of panic disorder (PD). It is also a factor that is considered to be central to PD but not major depressive disorder (MDD) – a related disorder that commonly co-occurs with PD. However, sensitivity to threat is a broad construct and it is unclear whether individuals with PD exhibit heightened initial threat reactivity, impairments in modulating their threat responding over time, or both. It is also unclear how these different facets of threat responding apply to predictable and/or unpredictable threat. The aim of the current study was to examine whether there are differences in initial threat reactivity and the time course of threat responding during predictable and unpredictable threat-of-shock in 186 adults with: 1) current PD and no history of depression (i.e., PD-only), 2) current MDD and no history of an anxiety disorder (i.e., MDD-only), 3) current comorbid PD and MDD, or 4) no lifetime history of psychopathology (i.e., controls). Threat responding was assessed using an electromyography startle paradigm. Relative to controls, individuals in the three psychopathology groups exhibited heightened initial threat reactivity to predictable and unpredictable threat and did not differ from each other. Multilevel mixed model analyses indicated that those with PD evidenced less of a decline over time in startle responding during unpredictable threat relative to those without PD. Those with MDD displayed a greater slope of decline in startle responding during predictable threat compared with those without MDD. The pattern of results suggests that there may be conceptual differences between measures of initial threat reactivity and time course of threat responding. Moreover, time course of threat responding, not initial threat reactivity, may differentiate PD from MDD.