The pedunculopontine nucleus (PPN) (or pedunculopontine tegmental nucleus, PPTN) is located in the brainstem, caudal to the substantia nigra and adjacent to the superior cerebellar peduncle. It is composed by a wide variety of neurochemical cell types, including cholinergic, glutamatergic and GABAergic cells. In the classical sense, the PPN is considered to be one of the main components of the reticular activating system. [WP,unvetted].