Bipolar disorder is a common major psychiatric disorder affecting 1±2% of the general population. It is a life-long illness representing a spectrum of disorders characterized by wide and distressing mood swings between manic and depressed [43]. In the past, the burden of the illness was underestimated. It must be recognized that the continuum of bipolar disorder spans from psychosocial and cognitive impairment to an increased risk of suicide [27].

The risk of future recurrences increases with each additional mood episode and in the majority of patients the illness progresses into a chronic recurrent course [43]. A widely considered hypothesis suggests that untreated bipolar illness may lead to pathophysiological changes in brain tissue of untreated patients [55]. This hypothesis has been supported by recent neuroradiological and postmortem neuropathological findings of structural changes in brain tissue of patients with bipolar disorder [19, 41]. However, despite extensive investigation, the precise neurobiology of bipolar disorder remains elusive.