The possible influence of electromagnetic field (EMF) on the function of neural systems has been widely concerned. In this article, we intend to investigate the effects of long term power frequency EMF exposure on brain cognitive functions and it's mechanism. The Sprague-Dawley (SD) rats were randomly divided into 3 groups: the rats in EMF Ⅰ group were placed in the 2 mT power frequency EMF for 24 days. The rats in EMF Ⅱ group were placed in the 2 mT power frequency EMF for 48 days. The rats in control group were not exposed to the EMF. Then, the 16 channel local field potentials (LFPs) were recorded from rats' prefrontal cortex (PFC) in each group during the working memory (WM) tasks. The causal networks of LFPs were also established by applying the directed transfer function (DTF). Based on that, the differences of behavior and the LFPs network connection patterns between different groups were compared in order to investigate the influence of long term power frequency EMF exposure on working memory. The results showed the rats in the EMF Ⅱ group needed more training to reach the task correction criterion (over 80%). Moreover, the causal network connection strength and the global efficiency of the rats in EMF Ⅰ and EMF Ⅱ groups were significantly lower than the corresponding values of the control group. Meanwhile, significant differences of causal density values were found between EMF Ⅱ group and the other two groups. These results indicate that long term exposure to 2 mT power frequency EMF will reduce the connection strength and the information transfer efficiency of the LFPs causal network in the PFC, as well as the behavior performance of the rats. These results may explain the effect of EMF exposure on working memory from the view of neural network connectivity and provide a support for further studies on the mechanism of the effect of EMF on cognition.
电磁场（EMF）作用对神经系统功能的影响，现已成为电磁生物效应领域广泛关注的问题。本文旨在从神经信息网络连接角度探究工频 EMF 长期作用对大脑认知功能的影响及其机制。本文将斯普拉格·道利（SD）大鼠随机分为 3 组，其中模型Ⅰ组将 SD 大鼠置于 2 mT 工频 EMF 中作用 24 d；模型Ⅱ组将 SD 大鼠置于 2 mT 工频 EMF 中作用 48 d；对照组 SD 大鼠未经工频 EMF 作用。随后，采集不同组别 SD 大鼠执行工作记忆（WM）任务过程中前额皮层（PFC）16 通道的局部场电位信号（LFPs），并基于定向传递函数（DTF）构建 LFPs 因果连接网络，最终通过对比各组 SD 大鼠在 WM 过程中 LFPs 信号因果网络特征参数及行为学表现的异同，探讨工频 EMF 长期作用对 WM 的影响。本文研究结果显示，模型Ⅱ组大鼠执行 WM 任务达到正确率 80% 以上所需时间及次数明显多于对照组。WM 任务中，模型Ⅰ、Ⅱ组因果网络连接强度及全局效率值均明显低于对照组；且模型Ⅱ组中因果网络连接密度值明显低于模型Ⅰ组及对照组。结果表明，经 2 mT 工频 EMF 的长期作用，PFC 的 LFPs 信号间因果网络连接强度及全局效率降低，并影响 SD 大鼠的行为学表现。本文的研究结果从神经网络信息传递的角度揭示了工频 EMF 作用影响大脑认知功能的可能机制，可为进一步研究其作用机制提供重要的支持。.
Keywords: connection pattern of causal network; local field potentials; long term exposure; power frequency electromagnetic field; working memory.