The Circular Nucleus (Circ) is a poorly understood hypothalamic structure located in the periventricular zone, surrounding the anterior commissure. This nucleus is part of the diencephalic continuum and participates in various autonomic, endocrine, and behavioral functions. While traditionally considered a minor structure, recent neuroanatomical studies have revealed important connections between the circular nucleus and neurodegenerative disease processes, particularly in Alzheimer's disease and Parkinson's disease.