Diurnal changes in core body temperature, day/night locomotor activity patterns, and actigraphy-generated behavioral sleep in aged canines with varying levels of cognitive dysfunction

•Diurnal rise in core body temperature present in old dogs (9–16 years) with peak at 19:00.•Lower peak body temperature in dogs with lowest spatial working memory ability.•Locomotor activity rhythm unchanged in dogs with impaired spatial working memory.•Impaired working memory related to more napping and lower afternoon body temperature.

Core body temperature (CBT) rhythm, locomotor activity, and actigraphy-sleep were evaluated in geriatric dogs with cognitive dysfunction. Dogs (n=33; 9–16 yrs) performed a spatial working memory task and divided into three memory groups: Low, Moderate, and High, with subsequent evaluation of learning and attention. Rectal CBT was recorded 6 times over a 17.5 h period and Actiwatch® activity monitoring system for 5 days while housed indoors with 12 h light/dark schedule. Rhythm of daily activity data was evaluated using the traditional cosinor analysis and generation of non-parametric measures of interdaily stability, intradaily variability, and relative amplitude. CBT differed with time (F (5, 130)=11.36, p<0.001), and was the highest at 19:00C. CBT at 19:00 was positively related (p<0.01) to memory (r(31)=0.50) and 3-domain cognitive performance index (memory, learning, attention; r(31)=0.39). Total daytime or night-time activity did not differ between memory groups, but hourly counts at 8:00 were positively related (p<0.05) to memory (r(31)=0.52), learning (r(31)=0.36), and 3-domain cognitive performance index (r(31)=0.53). There were no significant differences between age or memory groups for any circadian rhythm measures. Daytime naps were inversely related to memory accuracy (r(31)=−0.39; p<0.05) and BT at 15:00 (r(30)=−0.51; p<0.01). Lower peak BT and increased napping may predict some aspects of cognitive performance of working memory, learning, and/or attention processes in these geriatric dogs, but minimal diurnal rhythm disruption of locomotor activity is observed when these cognitive processes decline.