Strange B A, Fletcher P C, Henson R N, Friston K J, Dolan R J
Wellcome Department of Cognitive Neurology, Institute of Neurology, Queen Square, London WC1N 3BG, United Kingdom.
Proc Natl Acad Sci U S A. 1999 Mar 30;96(7):4034-9. doi: 10.1073/pnas.96.7.4034.
It is now accepted that hippocampal lesions impair episodic memory. However, the precise functional role of the hippocampus in episodic memory remains elusive. Recent functional imaging data implicate the hippocampus in processing novelty, a finding supported by human in vivo recordings and event-related potential studies. Here we measure hippocampal responses to novelty, using functional MRI (fMRI), during an item-learning paradigm generated from an artificial grammar system. During learning, two distinct types of novelty were periodically introduced: perceptual novelty, pertaining to the physical characteristics of stimuli (in this case visual characteristics), and exemplar novelty, reflecting semantic characteristics of stimuli (in this case grammatical status within a rule system). We demonstrate a left anterior hippocampal response to both types of novelty and adaptation of these responses with stimulus familiarity. By contrast to these novelty effects, we also show bilateral posterior hippocampal responses with increasing exemplar familiarity. These results suggest a functional dissociation within the hippocampus with respect to the relative familiarity of study items. Neural responses in anterior hippocampus index generic novelty, whereas posterior hippocampal responses index familiarity to stimuli that have behavioral relevance (i.e., only exemplar familiarity). These findings add to recent evidence for functional segregation within the human hippocampus during learning.
目前人们公认海马体损伤会损害情景记忆。然而，海马体在情景记忆中的确切功能作用仍不清楚。最近的功能成像数据表明海马体参与处理新奇性，这一发现得到了人体活体记录和事件相关电位研究的支持。在此，我们使用功能磁共振成像（fMRI），在由人工语法系统生成的项目学习范式中测量海马体对新奇性的反应。在学习过程中，会周期性地引入两种不同类型的新奇性：感知新奇性，与刺激的物理特征（在这种情况下是视觉特征）有关；范例新奇性，反映刺激的语义特征（在这种情况下是规则系统内的语法状态）。我们证明了左前海马体对这两种类型的新奇性均有反应，并且随着刺激熟悉度的增加这些反应会出现适应性变化。与这些新奇性效应形成对比的是，我们还显示随着范例熟悉度的增加双侧后海马体有反应。这些结果表明，就学习项目的相对熟悉度而言，海马体内存在功能分离。前海马体中的神经反应指示一般的新奇性，而后海马体的反应指示对具有行为相关性的刺激的熟悉度（即仅范例熟悉度）。这些发现为学习过程中人类海马体内功能分离的最新证据增添了内容。
