一、空间记忆的性质

Nature 522 (7556)

发表日期：2015年6月18日

空间工作记忆是通过额叶前部脑区域与海马体之间的活动协调来维持的，但一直不清楚这些区域之间的精确解剖联系是什么，也不清楚它们是在什么时间尺度上工作的。在这项研究中，Joshua Gordon及同事确定了额叶前部皮层与海马体之间的一个直接路径，该路径是空间提示信息的正确编码所必需的，但却并不是这些提示信息的维持和提取所需要的。海马体信息在空间工作记忆任务的编码阶段向额叶前部皮层中的神经单元流动，成功的编码需要这两个脑结构之间在网络活动的伽马频带内的同步。这些发现显示了海马体-额叶前部直接输入在空间信息的连续更新中的至关重要性。

原文题目：Hippocampal–prefrontal input supports spatial encoding in working memory。

原文摘要：Spatial working memory, the caching of behaviourally relevant spatial cues on a timescale of seconds, is a fundamental constituent of cognition. Although the prefrontal cortex and hippocampus are known to contribute jointly to successful spatial working memory, the anatomical pathway and temporal window for the interaction of these structures critical to spatial working memory has not yet been established. Here we find that direct hippocampal–prefrontal afferents are critical for encoding, but not for maintenance or retrieval, of spatial cues in mice. These cues are represented by the activity of individual prefrontal units in a manner that is dependent on hippocampal input only during the cue-encoding phase of a spatial working memory task. Successful encoding of these cues appears to be mediated by gamma-frequency synchrony between the two structures. These findings indicate a critical role for the direct hippocampal–prefrontal afferent pathway in the continuous updating of task-related spatial information during spatial working memory.

二、正面记忆的力量

Nature 522 (7556)

发表日期：2015年6月18日

回想正面记忆是否能减轻抑郁？Susumu Tonegawa 及同事利用与一个正面的、中性的或负面的经历相关的、通过光遗传学方法标记的特定海马体记忆印迹对这一问题进行了研究。这些记忆之后可以通过光被人工激活。正面印迹的急性激活被发现会抑制暴露于慢性压力的小鼠类似抑郁症的行为，这是由 “海马体-杏仁核-伏隔核”通道介导的一个效应。重要的是，正面印迹的慢性激活也会抑制处于压力状态下的小鼠类似抑郁症的行为，即便在激活已经结束以后也是这样，说明这种抗抑郁效应并不取决于对印迹的实时人工激活。作者提出，对与一个正面记忆相关的海马体齿状回细胞的直接激活，也许能为减轻一类与抑郁相关的行为提供一个潜在的治疗节点，尽管在目前阶段还不清楚这些发现对人类是否适用。

原文题目：Activating positive memory engrams suppresses depression-like behaviour.

原文摘要：Stress is considered a potent environmental risk factor for many behavioural abnormalities, including anxiety and mood disorders1, 2. Animal models can exhibit limited but quantifiable behavioural impairments resulting from chronic stress, including deficits in motivation, abnormal responses to behavioural challenges, and anhedonia3, 4, 5. The hippocampus is thought to negatively regulate the stress response and to mediate various cognitive and mnemonic aspects of stress-induced impairments2, 3, 5, although the neuronal underpinnings sufficient to support behavioural improvements are largely unknown. Here we acutely rescue stress-induced depression-related behaviours in mice by optogenetically reactivating dentate gyrus cells that were previously active during a positive experience. A brain-wide histological investigation, coupled with pharmacological and projection-specific optogenetic blockade experiments, identified glutamatergic activity in the hippocampus–amygdala–nucleus-accumbens pathway as a candidate circuit supporting the acute rescue. Finally, chronically reactivating hippocampal cells associated with a positive memory resulted in the rescue of stress-induced behavioural impairments and neurogenesis at time points beyond the light stimulation. Together, our data suggest that activating positive memories artificially is sufficient to suppress depression-like behaviours and point to dentate gyrus engram cells as potential therapeutic nodes for intervening with maladaptive behavioural states.

内容转载自《自然》中文版。