【作者】 蒋科杰；

【导师】 张雪娟；

【作者基本信息】 浙江师范大学 ， 基础数学， 2011， 硕士

【摘要】 人和动物在进行学习、记忆等高级认知的过程中,大脑的很多区域会产生不同频率范围的节律。这些节律一方面可以独立地发挥自己的作用,另一方面也可以相互作用、相互调节。一般低频率节律的相位会对高频率节律的振幅进行调节,使两者耦合起来产生嵌套的节律,从而生成更为复杂的大脑活动。经研究,这些嵌套的节律对于记忆的编码和再现有着至关重要的作用。通过数值模拟,我们发现在HH神经元网络中能产生两种频率范围的节律：theta节律(4-8Hz)和gamma节律(30-100Hz)。如果低频率的theta节律的相位对高频率的gamma节律的振幅进行适当地调节,那么将会产生theta嵌套的gamma节律。然而这种调节需要抑制性慢的神经元和抑制性快的神经元同时与兴奋性神经元之间存在突触连接,并且还需要足够强的外加刺激电流的刺激,缺少任何一种条件都将无法产生theta嵌套的gamma节律,即突触连接的电导系数gGAse、gGAfe和外加刺激电流Iapp不能为0。我们发现电导系数gGAse的增大会使theta节律的能量变大,从而使theta节律的相位和gamma节律的振幅的耦合(CFC:cross-frequency coupling)强度增大,而且在此过程中,各个兴奋性神经元之间的theta节律的相位同步性增加。然而随着电导系数ggGAfe的增大,产生的现象却完全相反。学习是大脑的一个重要功能,而由NMDA受体介导的电流与学习记忆密切相关。然而我们发现在一定条件下,如果只加强由NMDA受体介导的电流的电导系数gNMee,反而不会产生学习的效果。只有同时加强gNMes和由GABAA类受体介导的电流的电导系数gGAse,才会产生学习的效果。换言之,要产生学习这种现象需要NMDA受体和GABAA类受体的相互协调。在学习过程中,theta节律的能量增强,CFC强度增大,各个兴奋性神经元之间的theta节律的相位同步性增加。更多还原

【Abstract】 Multiple brain regions can generate rhythm in different frequency bands when animals, including humans, are undergoing cognitive tasks, such as learning, memory tasks and so on. These rhythms can occur simultaneously and work respectively, they can also interact with each other and much more complex brain activities can take place when nested rhythms generate as the amplitude of the high frequency rhythm is modulated by the phase of the low one. Resent research have indicated that these nested rhythms play an important role in memory coding and recalling.According to our computational simulation, we find that the HH neuronal net-work can generate both theta(4-8Hz) and gamma (30-100Hz)rhythm. And the theta-nested gamma rhythm occurs when the amplitude of high frequency gamma rhythm is modulated by the phase of low frequency theta rhythm. However, this modulating needs the synaptic connection from inhibitory fast neurons to excitatory neurons and the connection from inhibitory slow neurons to excitatory neurons, accompanied by the appropriate applied current. It is found that nested rhythm can’t generate if any one of these three terms is not available, namely the applied current Iapp, the synaptic conductances gGAse and gGAfe which can’t be zero. We find that the power of theta rhythm increases when the conductance gGAse increases, it leads to the increasing of the magnitude of phase-amplitude cross-frequency coupling(CFC) between theta and gamma rhythm, and the phase synchronization of theta rhythm among excited neurons increases in this process. However, a completely opposite result takes place when the conductance gGAfe increases.An important function of brain is to take charge of learning, and the current me-diated by NMDA receptor can facilitate learning. However, if we only increase the conductance gNMee, the learning activity can’t be aroused. Only when the conduc-tances gGAse and gNMes, as well as gNMee increase simultaneously, will the learning activity occur. In other words, the cooperation between NMDA receptor and GABAA receptor is the key for generating the learning effect. The power of theta rhythm in-crease during learning, and the magnitude of the phase-amplitude CFC also increases, but the phase synchronization of theta rhythm among excited neurons increases.更多还原