[Emotional endophenotypes and bipolar disorder]

Emotion can be described as a multidimensional affective state, accompanied with physiological, cognitive and subjective manifestations. Most bipolar patients spontaneously claim they have a higher sensitivity than average, which may lead to extreme emotional reactions, even during intercrisis periods. Few studies have focused on this particular affective dimension. Moreover, the emotional reactivity is a way to raise the question of bipolar patients' vulnerability to stress during euthymic periods. The aim of this study is to examine the emotional reactivity of euthymic bipolar patients in comparison with a control group, using a test of emotional induction with short films, in order to determine whether this particular affective dimension can be a potential endophenotype. Our hypothesis is that euthymic bipolar patients have a higher emotional reactivity than controls.

20 euthymic bipolar patients and 15 healthy control subjects were recruited. The emotional reactivity was assessed using a method of emotional induction, based on viewing a set of positive, negative and neutral short films. The subjects have to appreciate the valence (pleasant, unpleasant or neutral) and the arousal (degree of emotion triggered by each film), while physiological parameters (heart rate and galvanic skin response) were measured.

On average, euthymic bipolar patients report the same valence for each set of films and the same arousal to positive and negative movies as control subjects. Neutral pictures, however, were considered more moving by euthymic bipolar patients than by control subjects. Bipolar patient showed a higher heart rate than the control group, and no statistically difference was shown considering the galvanic skin response.

Euthymic bipolar patients seem to present an emotional hypereactivity which occurs especially during neutral situations.These results partly corroborate other authors outcomes, using a new and more ecologic methodology through an emotional induction by short films. While results of subjective evaluation are significant, results of physiological evaluation are controversial and need further exploration. This emotional hypereactivity during intercrisis periods allow us to understand the basal emotional functioning of bipolar patients, and could be linked with an emotional dysregulation, potential endophenotype of the bipolar disorder. It could have several clinical and research applications, particularly in the study of the emotional functioning of bipolar patients' first degree relatives.