HCRT and Parkinson disease: Orexin neurons are thought to be involved in PD pathology, based on impairments in arousal and sleep in PD and the major role of orexin neurons in these functions (Abbott et al., 2005; Dhawan et al., 2006; Baumann et al., 2008; Asai et al., 2009; Compta et al., 2009).