Enriched Physical Environment Attenuates Spatial and Social Memory Impairments of Aged Socially Isolated Mice.

Background: Social isolation (SI) in the elderly is one of the principal health risks in an ageing society. Physical environmental enrichment (EE) is shown to improve sensory, cognitive and motor functions, but it is unknown whether or not EE could protect against brain impairments caused by SI.

Methods: Eighteen-month-old mice were housed in either grouped or isolated, in a standard or enriched environment for 2 months, respectively. Behavioral tests were performed to evaluate cognitive functional and social interaction ability. Synaptic protein levels, myelination, neuroinflammation, brain derived neurotrophic factor (BDNF) and NOD-like receptor protein 3 inflammasome (NLRP3) signaling pathways were examined in the medial frontal cortex (mPFC) and hippocampus.

Results: Isolated aged mice exhibited declines in spatial memory and social memory, compared to age-matched littermates living within group housing. The aforementioned memory malfunctions were mitigated in isolated aged mice that were housed in a large cage with a running wheel and novel toys. Enriched housing prevented synaptic protein loss, myelination defects and downregulation of BDNF, while also increasing interleukin 1 beta and tumor necrosis factor alpha in the mPFC and hippocampus of isolated mice. In addition, activation of glial cells and NLRP3 inflammasomes was partially ameliorated in the hippocampus of isolated mice treated with physical EE.

Conclusions: These results suggests that an enriched physical environment program may serve as a non-pharmacological intervention candidate to help maintain healthy brain function of elderly people living alone.