Theta-gamma coupling in hippocampus during working memory deficits induced by low frequency electromagnetic field exposure

The dramatically increased use of electricity is raising major concerns as to the consequences of the interaction between electromagnetic field (EMF) and neurobiology. The aim of this study is to investigate the effects of magnetic field on working memory in the hippocampal region by analyzing local field potentials (LFPs) and spikes pattern in vivo. In present study, mice were exposed to EMF (50 Hz, 1 mT), static magnetic field (SMF, 1 mT), or placed in the exposure tube but without EMF exposure (SHAM), respectively. During the exposure for 7 consecutive days, mice were subjected to perform working memory (WM) tasks in Y-maze, and multichannel electrophysiology signals from hippocampus of mice were recorded during the test, from which LFPs, spike firing rates, band power at different frequencies, and theta-gamma modulation index (MI) were analyzed in details. From our results, correct choice rate during WM task was found significantly decreased in EMF group after 3 day exposure, which was consistent with noticeable decline in firing rate. Starting from Day 3 after EMF exposure, the power of theta (4-12 Hz) and gamma (LG, 30-60 Hz) before reference point (RP) in Y-maze were also found to be descending, together with decrease of oscillatory activities of theta and gamma frequencies. The results indicated that MI between theta and gamma could play a significant role in modulating the spikes discharge and encoding WM. Therefore, the analysis of theta-gamma coupling and its oscillation strength may provide a new perspective for mechanistic investigation of EMF-induced WM deficits.