A proposed function for hippocampal theta rhythm:: Separate phases of encoding and retrieval enhance reversal of prior learning
A proposed function for hippocampal theta rhythm:: Separate phases of encoding and retrieval enhance reversal of prior learning
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DOI：
10.1162/089976602317318965
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发表时间：
2002-04-01
影响因子：
2.9
通讯作者：
Wyble, BP
中科院分区：
文献类型：
--
作者：
Hasselmo, ME;Bodelón, C;Wyble, BP
探索期间大鼠海马脑电中出现θ节律，并显示与刺激获取的相位锁定。阻断θ节律的病变会损害需要逆转先前学习的任务的表现，包括T型迷宫中的逆转，其中一个手臂位置和食物奖励之间的关联需要被消除，而有利于相反的手臂位置和食物奖励之间的关联。在这里，海马模型显示了θ节律如何通过在每个100-300毫秒周期期间提供单独的功能阶段而对该任务中的逆转很重要，这与生理数据一致。在该模型中，新关联的有效编码发生在来自内嗅皮质的突触输入较强且来自海马CA 3区的兴奋性连接的长时程增强（LTP）较强，但来自CA 3区的突触电流较弱的阶段（以防止先前学习的关联的干扰）。当内嗅输入较弱而来自CA 3区的突触输入较强时，旧关联的恢复发生在这一阶段，但当来自CA 3区的突触发生去增强时（允许与当前输入不匹配的先前学习的关联消失）。这些阶段性变化要求CA 3区突触的LTP在突触传递最弱的阶段最强。与这些要求相一致，我们最近的数据表明，辐射层的突触传递在局部θ的正峰处最弱，这是以前的数据表明LTP的诱导在这一层中最强的时候。
The theta rhythm appears in the rat hippocampal electroencephalogram during exploration and shows phase locking to stimulus acquisition. Lesions that block theta rhythm impair performance in tasks requiring reversal of prior learning, including reversal in a T-maze, where associations between one arm location and food reward need to be extinguished in favor of associations between the opposite arm location and food reward. Here, a hippocampal model shows how theta rhythm could be important for reversal in this task by providing separate functional phases during each 100-300 msec cycle, consistent with physiological data. In the model, effective encoding of new associations occurs in the phase when synaptic input from entorhinal cortex is strong and long-term potentiation (LTP) of excitatory connections arising from hippocampal region CA3 is strong, but synaptic currents arising from region CA3 input are weak (to prevent interference from prior learned associations). Retrieval of old associations occurs in the phase when entorhinal input is weak and synaptic input from region CA3 is strong, but when depotentiation occurs at synapses from CA3 (to allow extinction of prior learned associations that do not match current input). These phasic changes require that LTP at synapses arising from region CA3 should be strongest at the phase when synaptic transmission at these synapses is weakest. Consistent with these requirements, our recent data show that synaptic transmission in stratum radiatum is weakest at the positive peak of local theta, which is when previous data show that induction of LTP is strongest in this layer.