Conversely, DR reduces Aβ levels (Patel et al., 2005; Wang et al., 2005; Halagappa et al., 2007), possibly by increasing activity of the non-amyloidogenic APP cleaving enzyme α-secretase (Qin et al., 2006), prevents tau hyperphosphorylation (Halagappa et al., 2007; Wu et al., 2008), possibly by reducing activity of the tau kinase cyclin dependent kinase-5 (CDK-5) (Wu et al., 2008), and prevents cognitive decline in these models, suggesting that DR exerts a neuro-protective effect upstream of Aβ and tau pathogenesis. Here, CDK5 is linked to Mental deterioration.