Background: Normothymic states in bipolar disorders are generally considered to be devoid of severe symptoms. However, bipolar patients present subsyndromal symptoms for half of their lives, and often have comorbid psychiatric disorders. If we go beyond the concept of temperamental features, can we identify certain emotional characteristics distinguishing normothymic bipolar patients from normal controls? We previously showed, using self-completed questionnaires, that normothymic bipolar patients display higher levels of emotional lability and intensity than controls.
Objectives: The aim of this study was to assess the emotional reactivity of normothymic bipolar patients, comparing such patients with a normal control group during an experimental mood induction procedure.
Method: We evaluated the subjective emotional reactivity of 145 subjects (90 control subjects and 55 normothymic bipolar patients), using an emotional induction method based on the viewing of a set of 18 pictures (6 positive, 6 negative, 6 neutral) extracted from the International Affective Picture System. Subjective valence and arousal were recorded with the Self-Assessment Manikin. We also recorded startle reflexes, triggered by a tone occurring during the viewing of two-thirds of the pictures. We controlled for confounding factors, such as concurrent treatments, in all analyses.
Results: Normothymic bipolar patients and normal controls assessed valence and arousal similarly for positive and negative images. However, neutral images were considered more pleasant [F(1,143) = 8.4; p = 0.004] and induced a higher level of arousal [F(1,143) = 12.3; p = 0.001] in normothymic bipolar patients than in control subjects. Neutral pictures also triggered a stronger startle reflex in normothymic bipolar patients compared to controls [F(3,123) = 3.1; p = 0.03].
Conclusion: Normothymic bipolar patients displayed emotional hyper-reactivity, mostly evidenced in neutral situations. This feature may be linked to emotional dysregulation and is a potential endophenotype and/or a risk factor for bipolar disorders. This trait may be responsible for vulnerability to minor stressful events in everyday life. These findings have potential implications for the daily management of bipolar disorder between crises.