Panic disorder : an integrative assessment of brain, body and cognitive function.

Abstract

Panic disorder is a highly generalised anxiety disorder in the sense that, even in the absence of panic, it is associated with wide–ranging abnormalities across multiple levels of function (e.g., central and peripheral physiology, behaviour, cognition, affect) (Friedman, 2007). Although the extant research literature has typically examined responses to explicitly threat–related stimuli in PD, it is increasingly recognised that panic disordered individuals differ from unaffected controls in their response to normatively non–threatening events, including ‘resting state’ paradigms (Grillon, 2008). In comparison to less integrative research designs, multivariate, multi–level research may more comprehensively characterise function during the disorder’s tonic, between–panic manifestation. The present research therefore examined PD in the between–panic state with an integrative psychophysiological and neuropsychological assessment comprising a range of normatively non–threatening paradigms. Clinical participants with current PD (n = 53) and demographically–matched healthy control participants (n = 106) completed an extensive laboratory–based assessment of brain, body and cognitive function, the results of which are reported as three studies. In Study 1, quantitative electroencephalography and autonomic (cardiovascular and electrodermal) measures were concomitantly recorded during two resting state conditions. The findings of this study demonstrate multiple abnormalities of brain and body function at rest in PD. Findings of note include diminished synchronised electrocortical activity within the alpha–1 frequency range, increased heart rate and decreased beat–to–beat heart rate modulation (i.e. heart rate variability) in PD compared to controls. In Study 2, event–related potential (ERP), autonomic and behavioural measures were obtained during performance of an auditory oddball task, to examine sensory information processing and the allocation of attention to goal–relevant, non–threatening stimuli in PD. Patients and controls differed on numerous ERP and behavioural indices. ERP findings of note include reduced P3 amplitude to infrequent auditory tones in PD compared to controls, and increased N1 amplitude to frequent, irrelevant tones. Study 3 examined cognitive function in PD with an extensive neuropsychological test battery comprising tests selected to assess the core cognitive domains of attention, memory, executive functions, language and sensory–motor function. The results support a selective deficit in the cognitive domain of sustained attention, but normative function in the other assessed cognitive domains. Considered together, many of the research findings indicate either impaired attentional processing or diminished capacity for attentional processing in PD. The findings also fit a theoretical model of diminished physiological flexibility, which proposes that in generalised anxiety disorders such as PD there is less physiological differentiation of baseline activity and stress–related reactivity to minor everyday and laboratory stressors (Thayer & Lane, 2000; Friedman, 2007; Hoehn–Saric, 2007). The integrative assessment identified numerous differences between patients and controls (i.e. disorder markers) spanning multiple levels of function. As different types of disorder markers (e.g., risk factors versus maintenance factors) may differentially benefit clinical practice and research (Zvolensky et al. 2006c), future research is needed to classify the identified markers so that their potential utility may be realised.