Participants
Twenty-one euthymic patients who met DSM-IV criteria for bipolar I disorder were recruited from the outpatient and inpatient wards of the Department of Neurology and Psychiatry of the Policlinico Umberto I Hospital – “Sapienza” University of Rome. Diagnoses were made by well-trained psychiatrists according to DSM-IV TR criteria [2]. The presence of a stable euthymic condition of at least one-month duration was established according to Hamilton Depression Rating Scale (HAM-D; [40]) scores (≤ 8) and of the Young Mania Rating Scale (YMRS; [41]) scores (≤ 6). Exclusion criteria comprised: comorbid axis I and II diagnosis; significant neurological or medical condition; psychiatric hospitalization within the previous six months; substance or alcohol abuse/dependence. All patients were under stabilized psychotropic medications, which were prescribed according to the most important international treatment guidelines for bipolar disorder [42-44]. Twenty-one healthy volunteers with no current or past psychiatric illness and no first-degree relative with affective disorder were recruited and matched to patients on the basis of age, sex, and education. Participants gave written informed consent to participate and the Local Research Ethics Committee approved the study.