Warwick Medical School, University of Warwick, Coventry CV4 7AL, United Kingdom.
Department of Neurosurgery, Cedars-Sinai Medical Center, Los Angeles, CA 90048.
J Neurosci. 2018 Apr 25;38(17):4200-4211. doi: 10.1523/JNEUROSCI.2312-17.2018. Epub 2018 Apr 3.
Cognitive psychologists have long hypothesized that experiences are encoded in a temporal context that changes gradually over time. When an episodic memory is retrieved, the state of context is recovered-a jump back in time. We recorded from single units in the medial temporal lobe of epilepsy patients performing an item recognition task. The population vector changed gradually over minutes during presentation of the list. When a probe from the list was remembered with high confidence, the population vector reinstated the temporal context of the original presentation of that probe during study, a neural contiguity effect that provides a possible mechanism for behavioral contiguity effects. This pattern was only observed for well remembered probes; old probes that were not well remembered showed an anti-contiguity effect. These results constitute the first direct evidence that recovery of an episodic memory in humans is associated with retrieval of a gradually changing state of temporal context, a neural "jump back in time" that parallels the act of remembering. Episodic memory is the ability to relive a specific experience from one's life. For decades, researchers have hypothesized that, unlike other forms of memory that can be described as simple associations between stimuli, episodic memory depends on the recovery of a neural representation of spatiotemporal context. During study of a sequence of stimuli, the brain state of epilepsy patients changed slowly over at least a minute. When the participant remembered a particular event from the list, this gradually changing state was recovered. This provides direct confirmation of the prediction from computational models of episodic memory. The resolution of this point means that the study of episodic memory can focus on the mechanisms by which this representation of spatiotemporal context is maintained and sometimes recovered.
认知心理学家长期以来一直假设，经验是在一个随时间逐渐变化的时间背景中编码的。当一个情景记忆被检索时，上下文的状态就会恢复——时间上的回溯。我们记录了癫痫患者在执行项目识别任务时内侧颞叶的单个神经元的活动。在呈现列表的过程中，群体矢量在几分钟内逐渐变化。当一个来自列表的探针被高度自信地记住时，群体矢量会恢复该探针在学习期间的原始呈现的时间上下文，这是一种神经连续性效应，为行为连续性效应提供了一种可能的机制。这种模式仅在记忆良好的探针中观察到；记忆不佳的旧探针则表现出反连续性效应。这些结果首次直接证明，人类情景记忆的恢复与逐渐变化的时间上下文状态的检索有关，这是一种与记忆行为相平行的神经“时间回溯”。情景记忆是从一个人的生活中重新体验特定经历的能力。几十年来，研究人员假设，与其他形式的记忆不同，后者可以简单地描述为刺激之间的关联，情景记忆依赖于时空背景的神经表示的恢复。在研究一系列刺激时，癫痫患者的大脑状态在至少一分钟内缓慢变化。当参与者从列表中记住一个特定的事件时，这个逐渐变化的状态就会被恢复。这直接证实了情景记忆计算模型的预测。这一点的解决意味着，情景记忆的研究可以集中于维持和有时恢复时空背景这种表示的机制上。
