The document discusses bipolar disorder (BD) and how it presents a challenge for researchers to understand due to its complex and variable nature. BD involves alternating between periods of depression and mania, but can be difficult to diagnose with confidence due to other possible diagnoses. The paper explores symptoms, potential neurological and genetic factors, and treatments for BD based on various studies. It frames BD as a "jigsaw puzzle" that researchers are piecing together through examining elements like brain networks, structural brain abnormalities, and genetic implications to help advance detection and management of the disorder.