Bipolar Disorder show cyclic changes of mood between depression (depressive phase) and mania (maniac phase). Vestibular tests have been shown high sensibility and specificity as a biological marker for major depression. This exploratory investigation will measure and compare the vestibular activity of bipolar disorder patients during different phases ( 6 depressed phase, 6 maniac phase, 6 euthimic and 6 control healthy subjects).