Buzsáki G
Department of Neurosciences, University of California, La Jolla 92093.
Neuroscience. 1989;31(3):551-70. doi: 10.1016/0306-4522(89)90423-5.
Review of the normally occurring neuronal patterns of the hippocampus suggests that the two principal cell types of the hippocampus, the pyramidal neurons and granule cells, are maximally active during different behaviors. Granule cells reach their highest discharge rates during theta-concurrent exploratory activities, while population synchrony of pyramidal cells is maximum during immobility, consummatory behaviors, and slow wave sleep associated with field sharp waves. Sharp waves reflect the summed postsynaptic depolarization of large numbers of pyramidal cells in the CA1 and subiculum as a consequence of synchronous discharge of bursting CA3 pyramidal neurons. The trigger for the population burst in the CA3 region is the temporary release from subcortical tonic inhibition. An overview of the experimentally explored criteria of synaptic enhancement (intensity, frequency, and pattern of postsynaptic depolarization, calcium influx, cooperativity, threshold) suggests that these requirements may be present during sharp wave-concurrent population bursts of pyramidal cells. Experimental evidence is cited showing that (a) population bursts in CA3 may lead to long-term potentiation in their postsynaptic CA1 targets, (b) tetanizing stimuli are capable of increasing the synchrony of the sharp wave-burst, and (c) activity patterns of the neocortical input to the hippocampus determine which subgroup of CA3 neurons will trigger subsequently occurring population bursts (initiator cells). Based on the experimental evidence reviewed a formal model of memory trace formation is outlined. During exploratory (theta) behaviors the neocortical information is transmitted to the hippocampus via the fast-firing granule cells which may induce a weak and transient heterosynaptic potentiation in a subgroup of CA3 pyramidal cells. The weakly potentiated CA3 neurons will then initiate population bursts upon the termination of exploratory activity (sharp wave state). It is assumed that recurrent excitation during the population burst is strongest on those cells which initiated the population event. It is suggested that the strong excitatory drive brought about by the sharp wave-concurrent population bursts during consummatory behaviors, immobility, and slow wave sleep may be sufficient for the induction of long-term synaptic modification in the initiator neurons of the CA3 region and in their targets in CA1. In this two-stage model both exploratory (theta) and sharp wave states of the hippocampus are essential and any interference that might modify the structure of the population bursts (e.g. epileptic spikes) is detrimental to memory trace formation.
对海马体中正常出现的神经元模式的回顾表明，海马体的两种主要细胞类型，即锥体神经元和颗粒细胞，在不同行为中活动最为活跃。颗粒细胞在与θ波同时出现的探索活动中达到最高放电率，而锥体细胞的群体同步性在静止、完成性行为以及与场尖波相关的慢波睡眠期间达到最大值。尖波反映了CA3锥体神经元爆发式同步放电导致CA1和下托中大量锥体细胞的突触后去极化总和。CA3区域群体爆发的触发因素是皮质下紧张性抑制的暂时解除。对实验探索的突触增强标准（强度、频率、突触后去极化模式、钙内流、协同性、阈值）的概述表明，这些条件可能在锥体细胞尖波同时出现的群体爆发期间存在。引用的实验证据表明：（a）CA3中的群体爆发可能导致其突触后CA1靶点的长期增强；（b）强直刺激能够增加尖波爆发的同步性；（c）海马体新皮质输入的活动模式决定了CA3神经元的哪个亚群将触发随后出现的群体爆发（启动细胞）。基于所回顾的实验证据，概述了一个记忆痕迹形成的形式模型。在探索性（θ波）行为期间，新皮质信息通过快速放电的颗粒细胞传递到海马体，这可能在CA3锥体细胞的一个亚群中诱导微弱且短暂的异突触增强。然后，微弱增强的CA3神经元将在探索活动终止时（尖波状态）引发群体爆发。据推测，群体爆发期间的反复兴奋在引发群体事件的那些细胞上最为强烈。有人提出，在完成性行为、静止和慢波睡眠期间，尖波同时出现的群体爆发所带来的强烈兴奋性驱动可能足以在CA3区域的启动神经元及其CA1靶点中诱导长期突触修饰。在这个两阶段模型中，海马体的探索性（θ波）和尖波状态都是必不可少的，任何可能改变群体爆发结构的干扰（如癫痫棘波）都对记忆痕迹形成有害。
