The sexually dimorphic nucleus, also known as the SDN, is a small cluster of neurons in the hypothalamus that is involved in sexual behavior and sexual orientation. Synonyms for the SDN include the sexually dimorphic area, the sexually dimorphic region, and the sexually dimorphic part of the hypothalamus. These terms all refer to the same part of the brain, which is known to be larger in males than in females and plays a key role in sexual differentiation during development. While the SDN has primarily been studied in relation to sexual behavior and orientation, recent research suggests that it may also play a role in other behaviors and functions, including aggression and stress responses.