Bipolar spectrum: Relevant psychological and biological factors

The bipolar spectrum is a concept which bridges bipolar I disorder and unipolar depression. As Kraepelin described, there may be continuity across mood disorders. If this is the case, why should we discriminate for drug choice For example, it is generally accepted that mood stabilizers should be used for the bipolar spectrum, whereas antidepressants are for unipolar depression. If these disorders are diagnostically continuous, it is possible that the same drug could be effective in treating both bipolar I disorder/spectrum and unipolar depression. To resolve this question, I would like to propose my hypothesis that there is an inflexion point which constitutes the boundary between the bipolar spectrum and unipolar depression. It is likely that this inflexion point consists of temperaments as, reportedly, there are many significant differences in the presence of various temperaments between the bipolar spectrum (bipolar II, II1/2 and IV) and unipolar depression. These findings suggest that temperaments could draw a boundary between the bipolar spectrum and unipolar depression. Moreover, it has been shown that certain temperaments may be associated with several biological factors and may be associated with drug response. As such, whilst the concept of the bipolar spectrum emphasizes continuity, it is the proposed inflexion point that discriminates drug responses between the bipolar spectrum and unipolar depression. At the moment, although hypothetical, I consider this idea worthy of further research.