School of Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, TX 75080, USA; Center for Vital Longevity, University of Texas at Dallas, Dallas, TX 75235, USA.
School of Behavioral and Brain Sciences, University of Texas at Dallas, Richardson, TX 75080, USA; Center for Vital Longevity, University of Texas at Dallas, Dallas, TX 75235, USA.
Neuroimage. 2015 Jan 15;105:21-31. doi: 10.1016/j.neuroimage.2014.10.046. Epub 2014 Oct 23.
fMRI was employed to investigate the relationship between pre-stimulus neural activity and associative encoding of words and pictures in humans. While undergoing scanning, subjects studied randomly interleaved word or picture pairs. A pre-stimulus cue preceded the presentation of each study pair and signaled whether it would comprise words or pictures. Memory for the study pairs was later tested with an associative recognition test, which comprised word or picture pairs presented either in the same (intact) or a different (rearranged) pairing as at study, along with pairs of new items. The critical fMRI contrast was between study activity associated with pairs later correctly judged intact and pairs incorrectly judged as rearranged. A key question was whether material-selective pre-stimulus encoding effects could be identified which overlapped regions selectively activated by the respective study material. Picture-selective pre-stimulus effects were identified in bilateral fusiform and the intraparietal sulcus (IPS), whereas word-selective effects could not be identified. Material-invariant pre-stimulus subsequent memory effects were also identified in several neocortical regions as well as in the hippocampus. Whereas the loci of the neocortical effects suggest that they reflect the benefit to encoding that accrues from engagement of cognitive control processes, their magnitude was negatively correlated across subjects with associative recognition performance and positively related to false alarm rate. Conversely, the hippocampal effects also predicted unique variance in associative memory and were negatively related to hit rate. It is suggested that the neocortical pre-stimulus effects may reflect encoding processes that increase familiarity of single items, whereas the hippocampal pre-stimulus effects are proposed to reflect either the encoding of task-irrelevant features or the retrieval of task-relevant information associated with the pre-stimulus cues. Overall, the results provide evidence that pre-stimulus processes may be deleterious, rather than beneficial, to associative encoding.
功能性磁共振成像（fMRI）被用于研究人类在刺激前的神经活动与单词和图片的联想编码之间的关系。在扫描过程中，受试者学习随机交错的单词或图片对。在呈现每个学习对之前，会有一个刺激前提示，提示它将包含单词还是图片。学习对的记忆后来通过联想识别测试进行测试，该测试包括以学习时相同（完整）或不同（重新排列）的配对呈现的单词或图片对，以及新的配对。关键的 fMRI 对比是在与后来正确判断为完整的对和错误判断为重新排列的对相关的研究活动之间进行的。一个关键问题是，是否可以识别出与各自研究材料选择性激活的区域重叠的材料选择性刺激前编码效应。在双侧梭状回和顶内沟（IPS）中识别出了图片选择性刺激前效应，而不能识别出单词选择性效应。在几个新皮层区域以及海马体中还识别出了材料不变的刺激前后续记忆效应。虽然新皮层效应的位置表明它们反映了认知控制过程参与带来的对编码的益处，但它们的幅度在受试者之间呈负相关，与联想识别表现呈负相关，与虚报率呈正相关。相反，海马体效应也预测了联想记忆的独特方差，与击中率呈负相关。研究表明，新皮层刺激前效应可能反映了增加单个项目熟悉度的编码过程，而海马体刺激前效应则可能反映了与刺激前提示相关的任务无关特征的编码或任务相关信息的检索。总的来说，这些结果提供了证据表明刺激前过程可能对联想编码有害，而不是有益。
