Does Spontaneous Physical Activity Level Determine Cognitive Benefits From The Environmental Enrichment?

Environmental enrichment (EE) promotes a variety of positive effects on brain function. However, it is controversial whether EE remains beneficial in the absence of wheel running. Such confusion may be the result of differences in spontaneous physical activity level. Nevertheless, in EE experiments where multiple rodents were housed in a cage, individual spontaneous physical activity level has not been measured due to the technical difficulties. PURPOSE: We tested the hypothesis that cognitive benefits arising from EE are associated with spontaneous physical activity level (wheel running and/or other locomotor activity). METHODS: Wistar rats were divided into four different housing groups: EE (running wheel and objects: slope, tunnel, and hut), running wheel only (EE-R), objects only (EE-O), and standard environment (SE) (N = 7-8/group). Physical activity level of each rat was continuously recorded using an embedded three-axis accelerometer. After exposure to each condition for 4 weeks, the animals were submitted to the Morris water maze (MWM) test. The MWM test was carried out on 4 consecutive days, and spatial learning and memory was assessed using time to find the platform. RESULTS: Physical activity level was higher in the EE (260,350 ± 9,203 a.u./week) and EE-R(205,018 ± 8562 a.u./week) compared with the SE (13,745 ± 945 a.u./week, Ps < 0.05). There was no difference in physical activity level between the EE-O (16,770 ± 1,200 a.u./week) and the SE. In the MWM, the time to find the platform was shorter in the EE groups (EE: 15.5 ± 3.0, EE-R: 11.4 ± 3.5, EE-O: 11.6 ± 4.5 sec) than the SE group (29.9 ± 3.0 sec, Ps < 0.05) on day 3. Physical activity level among the groups was not correlated with the time to find the platform (R2 = 0.22). CONCLUSION: The EE-O enhanced cognitive function despite lower physical activity level. The present investigation suggests that spontaneous physical activity level alone does not determine hippocampus-dependent cognition in the environmental enrichment conditions.: