Aging dogs exhibit heterogeneous cognitive decline trajectories: A longitudinal comparative model

BackgroundBoth dogs and humans experience substantially variable cognitive decline with age. In humans, this ranges from healthy cognitive aging to early onset Alzheimer's disease. While different rates of cognitive decline have been described in purpose-bred beagles, few studies have examined longitudinal trajectories in companion dogs.ObjectiveThe aim of this study was to describe cognitive changes in a cohort of 92 senior dogs (aged ≥ 8 years).MethodsData were collected on 7 cognitive outcomes (2 caregiver questionnaires and 5 cognitive tests) every 6 months from enrollment to withdrawal/death. A principal components analysis reduced the dimensionality of these outcomes into a single global cognitive score. A mixed effect model was built using this composite score to examine within-subjects cognitive changes, while accounting for chronological age and study participation effects. Finally, a hierarchical cluster analysis identified statistically distinct groups of cognitive trajectories.ResultsAll seven outcomes loaded strongly, with consistent directionality, onto the first principal component (PC1) at each timepoint. Global cognitive score significantly declines with increasing age (β = -0.60, p < 0.0001). Despite a non-significant population-level subject*age interaction (p = 0.14), individual random slopes (rate of change with age) ranged from -0.20 and 0.15, suggesting meaningful variability. Cluster analysis revealed two groups differing in trajectories at the population level and subject level.ConclusionsThese findings provide evidence that while age is a significant predictor of cognitive decline at the population level, individual trajectories vary. The heterogeneity of canine cognitive aging presents an opportunity to investigate the biologic drivers of age-associated cognitive decline.