Stanford University, USA.
J Cogn Neurosci. 2010 Jan;22(1):156-73. doi: 10.1162/jocn.2009.21195.
The essential role of the medial temporal lobe (MTL) in long-term memory for individual events is well established, yet important questions remain regarding the mnemonic functions of the component structures that constitute the region. Within the hippocampus, recent functional neuroimaging findings suggest that formation of new memories depends on the dentate gyrus and the CA(3) field, whereas the contribution of the subiculum may be limited to retrieval. During encoding, it has been further hypothesized that structures within MTL cortex contribute to encoding in a content-sensitive manner, whereas hippocampal structures may contribute to encoding in a more domain-general manner. In the current experiment, high-resolution fMRI techniques were utilized to assess novelty and subsequent memory effects in MTL subregions for two classes of stimuli--faces and scenes. During scanning, participants performed an incidental encoding (target detection) task with novel and repeated faces and scenes. Subsequent recognition memory was indexed for the novel stimuli encountered during scanning. Analyses revealed voxels sensitive to both novel faces and novel scenes in all MTL regions. However, similar percentages of voxels were sensitive to novel faces and scenes in perirhinal cortex, entorhinal cortex, and a combined region comprising the dentate gyrus, CA(2), and CA(3), whereas parahippocampal cortex, CA(1), and subiculum demonstrated greater sensitivity to novel scene stimuli. Paralleling these findings, subsequent memory effects in perirhinal cortex were observed for both faces and scenes, with the magnitude of encoding activation being related to later memory strength, as indexed by a graded response tracking recognition confidence, whereas subsequent memory effects were scene-selective in parahippocampal cortex. Within the hippocampus, encoding activation in the subiculum correlated with subsequent memory for both stimulus classes, with the magnitude of encoding activation varying in a graded manner with later memory strength. Collectively, these findings suggest a gradient of content sensitivity from posterior (parahippocampal) to anterior (perirhinal) MTL cortex, with MTL cortical regions differentially contributing to successful encoding based on event content. In contrast to recent suggestions, the present data further indicate that the subiculum may contribute to successful encoding irrespective of event content.
内侧颞叶(MTL)在个体事件的长期记忆中起着至关重要的作用,但关于构成该区域的组成结构的记忆功能仍存在一些重要问题。在海马体中,最近的功能神经影像学研究结果表明,新记忆的形成依赖于齿状回和 CA(3) 区,而下托的贡献可能仅限于检索。在编码过程中,进一步假设 MTL 皮层内的结构以内容敏感的方式有助于编码,而海马体结构可能以更广泛的方式有助于编码。在当前的实验中,使用高分辨率 fMRI 技术来评估两种刺激——面孔和场景——在 MTL 亚区的新颖性和随后的记忆效应。在扫描过程中,参与者执行了一项带有新的和重复的面孔和场景的附带编码(目标检测)任务。随后的识别记忆被索引为扫描过程中遇到的新刺激。分析显示,所有 MTL 区域都对新颖的面孔和新颖的场景敏感。然而,在边缘回、内嗅皮层和包括齿状回、CA(2) 和 CA(3) 的组合区域中,相同比例的体素对新颖的面孔和场景敏感,而旁海马回、CA(1) 和下托则对新颖的场景刺激更为敏感。与这些发现平行的是,在边缘回中观察到了面孔和场景的后续记忆效应,编码激活的幅度与后来的记忆强度有关,这由跟踪识别置信度的分级响应来表示,而在旁海马回中,后续记忆效应是场景选择性的。在海马体中,下托的编码激活与两种刺激类别的后续记忆相关,编码激活的幅度以分级的方式随后来的记忆强度而变化。总的来说,这些发现表明,从后部(旁海马)到前部(边缘回)MTL 皮层的内容敏感性呈梯度分布,MTL 皮层区域根据事件内容的不同,对成功编码的贡献也不同。与最近的观点相反,本研究进一步表明,下托可能有助于成功编码,而与事件内容无关。