Disordered Hippocampal Reactivations Predict Spatial Memory Deficits in a Mouse Model of Alzheimer's Disease

Alzheimers disease (AD) is characterised by progressive memory decline associated with hippocampal degeneration. However, the specific physiological mechanisms underlying hippocampal dysfunction in AD remain poorly understood and improved knowledge may aid both diagnosis and help identify new avenues for therapeutic intervention. We investigated how disruptions in hippocampal reactivations relate to place cell stability and spatial memory deficits in an AD mouse model. Using the APP knock-in mouse model NL-G-F, we conducted simultaneous behavioural and electrophysiological recordings in a radial arm maze. NL-G-F mice exhibited significant impairments in memory performance, demonstrated by an increased propensity to revisit arms, compared to wild-type controls. These memory deficits were associated with a reduction in the stability of hippocampal place cells, which occurred over short timescales and was accentuated across rest. While the rate of hippocampal reactivation events during rest was unchanged, the structure of these events was significantly degraded in NL-G-F mice. The decreased structure of reactivations was predictive of decreased stability in place cell firing. These findings suggest that disrupted reactivation sequences may act as a mechanism of memory disorder in AD.