Introduction
Bipolar Disorder (BD) is a chronic and recurrent mental illness, found in approximately 3% of the general population [1]. Typically, BD is characterized by extreme changes in mood polarity (mania and depression) with intervening periods of euthymia [2]. Growing evidence has revealed that patients with BD may experience poor social functioning in several areas such as such as independent living, interpersonal relationships, occupational and educational achievement, recreational enjoyment, and sexual activity [3], and that these dysfunctions persist even during the clinical remission of symptoms or euthymia [4]. Social difficulties have also been demonstrated in laboratory tasks. Euthymic BD patients can be impaired at recognising faces and identifying facial expressions of emotion [5-8]. Behavioural deficits in the recognition and naming of facial emotions may be mediated by perturbations within the neural circuit including the ventral visual pathway, amygdala and ventrolateral prefrontal regions [9-11]. Consistent with this view, using affective faces tasks, previous studies have shown amygdala dysfunctions in maniac bipolar patients [12-14] and a dysfunction of the ventrolateral prefrontal cortex during both mania [12, 15, 16] and euthymia [17-20]. Given the associations between these brain areas and eye gaze processing, the aim of the present study was to explore the extent to which euthymic BD patients may show anomalies in the processing of eye-regions of the face. In particular, two important aspects of eye-gaze processing were assessed: the ability to infer the mental state and intention of others from the eyes (reading the mind in the eyes) and the tendency to follow the direction of another individual’s gaze (social attention).