Department of Neurosciences, University of California, San Diego, California, USA.
J Neurophysiol. 2011 Apr;105(4):1454-63. doi: 10.1152/jn.00902.2010. Epub 2011 Jan 19.
The process of associating items encountered over time and across variable time delays is fundamental for creating memories in daily life, such as for stories and episodes. Forming associative memory for temporally discontiguous items involves medial temporal lobe structures and additional neocortical processing regions, including prefrontal cortex, parietal lobe, and lateral occipital regions. However, most prior memory studies, using concurrently presented stimuli, have failed to examine the temporal aspect of successful associative memory formation to identify when activity in these brain regions is predictive of associative memory formation. In the current study, functional MRI data were acquired while subjects were shown pairs of sequentially presented visual images with a fixed interitem delay within pairs. This design allowed the entire time course of the trial to be analyzed, starting from onset of the first item, across the 5.5-s delay period, and through offset of the second item. Subjects then completed a postscan recognition test for the items and associations they encoded during the scan and their confidence for each. After controlling for item-memory strength, we isolated brain regions selectively involved in associative encoding. Consistent with prior findings, increased regional activity predicting subsequent associative memory success was found in anterior medial temporal lobe regions of left perirhinal and entorhinal cortices and in left prefrontal cortex and lateral occipital regions. The temporal separation within each pair, however, allowed extension of these findings by isolating the timing of regional involvement, showing that increased response in these regions occurs during binding but not during maintenance.
在日常生活中，例如在故事和情节中，将随时间和不同时间延迟遇到的项目关联起来的过程是创建记忆的基础。形成时间上不连续项目的联想记忆涉及内侧颞叶结构和额外的新皮质处理区域，包括前额叶皮层、顶叶和外侧枕叶区域。然而，大多数先前的记忆研究使用同时呈现的刺激，未能检查成功联想记忆形成的时间方面，以确定这些大脑区域的活动何时可预测联想记忆形成。在当前的研究中，当受试者看到具有固定对内延迟的连续呈现的视觉图像对时，获取功能磁共振成像数据。这种设计允许从第一个项目的开始，通过 5.5 秒的延迟期，以及第二个项目的结束，分析整个试验的时间过程。然后，受试者完成了对他们在扫描期间编码的项目和联想的扫描后识别测试，以及他们对每个项目的信心。在控制项目记忆强度后，我们分离出专门参与联想编码的大脑区域。与先前的发现一致，在前内侧颞叶区域的左侧海玛和内嗅皮层以及左侧前额叶皮层和外侧枕叶区域发现了增加的区域活动，预测了随后的联想记忆成功。然而，每对之间的时间分离允许通过隔离区域参与的时间来扩展这些发现，表明这些区域的反应增加发生在绑定期间而不是维持期间。
