The Dorsolateral Prefrontal Cortex Plays a Role in Self-Initiated Elaborative Cognitive Processing during Episodic Memory Encoding: rTMS Evidence

During episodic memory encoding, elaborative cognitive processing can improve later recall or recognition. While multiple studies examined the neural correlates of encoding strategies, few studies have explicitly focused on the self-initiation of elaborative encoding. Repetitive transcranial magnetic stimulation (rTMS), a method which can transiently disrupt neural activity, was administered during an associative encoding task. rTMS was either applied to the left dorsolateral prefrontal cortex (DLPFC) or to the vertex (a control region not involved in memory encoding) during presentation of pairs of words. Pairs could be semantically related or not related. Two encoding instructions were given, either cueing participants to analyze semantic relationships (cued condition), or to memorize the pair without any specific strategy cues (the self-initiated condition). Participants filled out a questionnaire regarding their use of memory strategies and performed a cued-recall task. We hypothesized that if the DLPFC plays a role in the self-initiation of elaborative encoding we would observe a reduction in memory performance in the self-initiated condition, particularly for related. We found a significant correlation between the effects of rTMS and strategy use, only in the self-initiated condition with related pairs. High strategy users showed reduced performance following DLPFC stimulation, while low strategy users tended to show increased recall following DLPFC stimulation during encoding. These results suggest the left DLPFC may be involved in the self-initiation of memory strategy use, and individuals may utilize different neural networks depending on their use of encoding strategies.在情景记忆编码过程中，精细认知加工可提升后续的回忆或再认成绩。尽管已有多项研究探讨了编码策略的神经关联物，但极少有研究专门关注精细编码的自我启动过程。重复经颅磁刺激（repetitive transcranial magnetic stimulation, rTMS）是一种可短暂干扰神经活动的技术，本研究在联想编码任务期间施加了该刺激。在单词对呈现阶段，rTMS分别施加于左侧背外侧前额叶皮层（left dorsolateral prefrontal cortex, DLPFC）或顶点（一个不参与记忆编码的对照脑区）。单词对可分为语义相关与非语义相关两类。实验设置了两种编码指导语：一种提示被试分析语义关系（提示条件），另一种要求被试记忆单词对但不提供任何特定策略提示（自我启动条件）。被试需填写一份关于记忆策略使用情况的问卷，并完成一项线索回忆任务。我们提出假设：若左侧背外侧前额叶皮层参与精细编码的自我启动过程，那么在自我启动条件下（尤其是针对语义相关单词对），我们将观察到被试的记忆成绩下降。研究结果显示，仅在自我启动条件下的语义相关单词对中，rTMS的刺激效应与记忆策略使用情况存在显著相关性。高策略使用组被试在左侧背外侧前额叶皮层接受刺激后的记忆成绩有所下降，而低策略使用组被试在编码阶段接受该刺激后的回忆成绩则趋于提升。上述结果表明，左侧背外侧前额叶皮层可能参与记忆策略使用的自我启动过程，且个体可能根据自身编码策略的使用情况调用不同的神经网络。