Neuroimaging and pathohistologic research may show whether bipolar disorder is a degenerative and progressive condition, if detectable changes in the brain record past occurrences, and whether these changes are reversible. Interpreting neuroimaging studies has been complicated by a lack of identification of patient mood states and differences in patients' medication status, but several observations have been made. Pathohistologic research suggests that bipolar disorder is associated with significant cell pathology.