SPN and Huntington disease: Note, however, that the phenomenon of increased responsiveness of GPe neurons to iSPN activation was not seen in YAC128, R6/1, or R6/2 mice (Akopian, Barry, Cepeda, & Levine, 2016; Barry et al., 2018; Du et al., 2016), and may represent an early stage of HD pathophysiology prior to SPN loss.