The probe test confirmed that hM4Di-expressing APP/PS1-PV-Cre mice had also no memory impairments as they spent significantly more time in the target quadrant, similar to WT-PV-Cre mice, whereas mCherry-expressing APP/PS1-PV-Cre mice showed a clear memory deficit and performed at chance level (Fig. 7c). The gene discussed is APP; the disease is memory impairment.