The term intercalated periaqueductal gray refers to a small group of neurons staining for nitiric oxide synthase (NADPH-diaphorase) in the periaqueductal gray of the human. They are located about one third of the length of the periqueductal gray from its caudal extreme. The cells are distributed on both sides of the boundary between the lightly staining lateral periaqueductal gray and ventrolateral periaqueductal gray ( Carrive-2012 ). Functionally the intercalated periaqueductal gray belongs to the motor periaqueductal gray of the behavior control column in the cerebrospinal trunk ( Swanson-2004 ).