Targeting <scp>CA2</scp> Perineuronal Nets Restores Recognition Memory and Theta Oscillations in Aged Mice

Remembering familiar versus novel stimuli is fundamental to survival, but it is compromised in several neurodegenerative disorders where aging is a key factor. Although the components of the extracellular matrix (ECM) have been suggested to be implicated in memory maintenance, the mechanistic and behavioral roles of ECM during the aging process remain unclear. Here, we employed an accelerated mouse model of aging to elucidate the causal link between ECM dynamics and recognition memory during aging. Aged mice exhibited impaired social and non-social recognition memory, accompanied by increased intensity of perineuronal nets (PNNs), specialized ECM structures in the hippocampal dorsal CA2 (dCA2). A reduction in the power of theta oscillations (3-7 Hz) in the dCA2 of aged mice was also observed. Notably, selective degradation of PNNs in the dCA2 using chondroitinase ABC (ChABC) rescued recognition memory deficits and restored theta oscillations. Together, our findings identify abnormal PNN in the CA2 as a critical factor for age-related deficits in hippocampal-dependent recognition memory and network rhythmicity. These insights raise the possibility that targeting CA2 PNNs could facilitate the development of diagnostic and therapeutic strategies to address age-associated cognitive frailty.