The Perirhinal Cortex and Implicit Memory

许多关于人类长期记忆的理论认为，对先前事件的外显记忆依赖于内侧颞叶(MTL)及其亚区。相比之下，内隐记忆被认为依赖于MTL以外的皮质区域。内隐记忆是在任务中测量的，其中与先前物品的经验有助于随后识别或产生该物品。然而，最近有人假设，无论意识或意图如何，MTL中的一个区域--口周皮质--拥有高水平的概念和知觉表征。在最近的一项研究中，我们提供了证据表明，大脑周围皮质对某些形式的内隐记忆很敏感。我们证明，健忘性中风和颞叶切除术患者的概念内隐记忆受损，在另一项单独的实验中，编码时的周围激活预测了随后的概念内隐记忆。 这里提出的实验试图扩展这些先前的发现。在第一个实验中，一种测量概念内隐记忆和基于外显熟悉的再认的新范式将被用来评估大脑周围皮质在这两个任务中的作用。参与者将在分别测量熟悉度和概念内隐记忆的识别和自由联想记忆任务中接受扫描。在第二个实验中，我们将检验这一假设，即在知觉内隐记忆任务的编码和提取阶段，足够复杂的知觉辨别将招募周围皮层。这两个实验都将利用高分辨率的fMRI和通过手动MRI脑跟踪得出的感兴趣区域对齐。此外，在第一个实验中，我们将开发一种独特的fMRI序列，旨在抵消公开语音固有的运动伪像。 了解周围皮层处理和表达概念和知觉信息的条件，对于理解MTL在长期记忆和其他方面的作用至关重要。来自这些研究的见解可以应用于诊断、理解和治疗对记忆产生不利影响的记忆缺陷和精神障碍。

Many theories of human long term memory assume that explicit memory for prior events relies on the medial temporal lobes (MTLs) and its subregions. In contrast, implicit memory, measured in tasks where experience with a prior item facilitates the subsequent identification or production of that item, is thought to rely on cortical regions outside of the MTL. However, it has recently been hypothesized that the perirhinal cortex, a region within the MTL, holds high level conceptual and perceptual representations irrespective of awareness or intention. In one recent study, we provided evidence that the perirhinal cortex is sensitive to certain forms of implicit memory. We demonstrated that amnesic stroke and temporal lobectomy patients exhibited impaired conceptual implicit memory, and in a separate experiment showed that perirhinal activations at encoding predicted subsequent conceptual implicit memory. The experiments proposed here seek to extend these previous findings. In the first experiment, a novel paradigm that measures both conceptual implicit memory and explicit familiarity-based recognition will be used to assess the role of the perirhinal cortex in these two tasks. Participants will be scanned during recognition and free association memory tasks that measure familiarity and conceptual implicit memory, respectively. In the second experiment we will test the hypothesis that sufficiently complex perceptual discriminations will recruit the perirhinal cortex during both the encoding and retrieval phases of a perceptual implicit memory task. Both experiments will utilize high-resolution fMRI and region of interest alignment derived from manual MRI brain tracing. Moreover, for the first experiment we will develop a unique fMRI sequence designed to counteract movement artifacts intrinsic to overt speech. Understanding the conditions under which the perirhinal cortex processes and represents conceptual and perceptual information is critical to understanding the role of the MTLs in long term memory and beyond. The insights from these studies can be applied to diagnose, understand, and treat memory deficits and mental disorders that adversely affect memory.