What Do Patient-Control Studies of Habituation in Anxiety and Stress Disorders Reveal?

Habituation, a fundamental form of learning characterized by a diminished response to repeated stimuli, has been linked to emotional regulation and implicated in anxiety and stress-related disorders. This systematic review investigated whether individuals with these conditions exhibit consistent alterations in habituation compared to healthy controls. Thirty-three studies, published over five decades, were analyzed. These studies encompassed 84 patient-control comparisons across various psychophysiological measures, including electrodermal activity, heart rate, and the eyeblink reflex. The most frequent pattern (29 comparisons) was the absence of statistically reliable differences in either initial response magnitude or habituation rate, which may reflect genuinely small or absent group differences, limited statistical power, or both. The subsequent most frequent patterns observed were higher initial responsiveness combined with slower habituation (11 comparisons) or normal responsiveness with slower habituation (10 comparisons). Furthermore, descriptive trends revealed that in 52% of comparisons, patients showed higher initial responsiveness than controls, and in 64%, they showed slower habituation; both trends co-occurred in only 37% of the comparisons. Thus, although suggestive data exist, the predominant view that anxious individuals exhibit exaggerated responses and disrupted habituation is not fully supported by the current body of reliable evidence. This review highlights limitations in the existing literature, notably methodological variability and small sample sizes, and emphasizes the importance of phenotype-based approaches. Future research would benefit from statistically rigorous and adequately powered designs, improved modeling strategies, greater attention to stimulus parameters, and broader use of retention and specificity tests to elucidate the nature of habituation deficits in clinical populations.