There’s been reports for some time that people suffering from mental disorders with psychotic episodes, like schizophrenia and bipolar disorder, will have different symptoms in their different languages if they speak more than one. One early report of this is from 1895, of a Welsh sailor who would change between a Welsh-speaking, passive and depressed personality and a English-speaking, manic personality where neither would remember the life stories of the other. Psychiatric reports from back then may not always be entirely reliable, but more recent observations have some lessons to tell. 

Although this is a bit heavy material for this blog, there are also some interesting observations about bilingualism in healthy individuals. Imagine the psychosis as taking some differences already there and turning up the volume to the maximum. A recent scientific review article reviews some of the observations made and also some observations about bilingualism in general that may explain what is going on:  (more…)