Impairment of Neural Rhythms in the Hippocampus in Different Behavioral Phases Induced by Amyloid- Accumulation

Alzheimer's disease (AD) is a neurodegenerative disease in which A beta accumulation occurs early in the disease. It is characterized by memory loss and progressive neurocognitive dysfunction. Theta rhythm, slow gamma rhythm and fast gamma rhythm of the hippocampus exhibit important contributions to the encoding and retrieval of memory. Previous studies have shown that gamma rhythms were impaired in AD model animals under free exploration behaviors. However, little is known about how the neural dynamics is changed under spatial memory state as AD rats performed a mnemonic task. We recorded the local field potential of hippocampal CA1 in rats during the free exploration task and a delayed match-to-sample spatial memory task, and the effects of A beta on neural rhythm in two behavioral phase were analyzed. Our study found that injection of Ab reduced the power of slow gamma and fast gamma during the free exploration phase, while the decrement of fast gamma power was further exacerbated during the memory phase. In addition, A beta also reduces the theta-fast gamma coupling strength in the free exploration phase. These findings provide new evidence for impairment of high frequency neural rhythm during memory phase of AD model rats, which could be a potential target of neural modulation for AD.