Blink reflex under external emotional-stimuli in bipolar I and II disorders

Bipolar disorder types I (BD I) and II (BD II) might present different cortico-brainstem circuit dysfunctions under external emotions, which might be reflected by the blink reflex. We therefore invited 32 BD I and 23 BD II patients, and 46 healthy volunteers to answer the Mood Disorder Questionnaire, the Hypomania Checklist-32, and the Plutchik - van Praag Depression inventory, and to undergo the blink reflex test under external emotions (emotional pictures plus sounds) of Disgust, Erotica, Fear, Happiness, and Sadness. Compared to healthy controls, BD I showed prolonged R2/R2′ latencies under most emotions, and their PVP scores were negatively correlated with the areas under curve (AUCs) of R2 and R2′ under Erotica; and BD II showed reduced R2/R2′ AUCs under all emotions. Moreover, R2′ AUCs under Disgust, Fear, and Happiness were significantly reduced in BD II than those in BD I. Our results have shown that, irrespective of patients' on-going affective states, the R2/R2′ components were delayed in BD I but suppressed in BD II under most external emotions. Our study provides some hints to distinguish the two types of bipolar disorder, referring to the cortico-brainstem circuit dysfunctions under external emotions.