Wagner A D, Koutstaal W, Maril A, Schacter D L, Buckner R L
Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Cereb Cortex. 2000 Dec;10(12):1176-84. doi: 10.1093/cercor/10.12.1176.
Previous neuroimaging studies have shown that activation in left inferior prefrontal cortices (LIPC) is reduced during repeated (primed) relative to initial (unprimed) stimulus processing. These reductions in anterior (approximately BA 45/47) and posterior (approximately BA 44/6) LIPC activation have been interpreted as reflecting implicit memory for initial semantic or phonological processing. However, prior studies do not unambiguously indicate that LIPC priming effects are specific to the recapitulation of higher-level (semantic and/or phonological), rather than lower-level (perceptual), processes. Moreover, no prior study has shown that the patterns of priming in anterior and posterior LIPC regions are dissociable. To address these issues, the present fMRI study examined the nature of priming in LIPC by examining the task-specificity of these effects. Participants initially processed words in either a semantic or a nonsemantic manner. Subsequently, participants were scanned while they made semantic decisions about words that had been previously processed in a semantic manner (within-task repetition), words that had been previously processed in a nonsemantic manner (across-task repetition), and words that had not been previously processed (novel words). Behaviorally, task-specific priming was observed: reaction times to make the semantic decision declined following prior semantic processing but not following prior nonsemantic processing of a word. Priming in anterior LIPC paralleled these results with signal reductions being observed following within-task, but not following across-task, repetition. Importantly, neural priming in posterior LIPC demonstrated a different pattern: priming was observed following both within-task and across-task repetition, with the magnitude of priming tending to be greater in the within-task condition. Direct comparison between anterior and posterior LIPC regions revealed a significant interaction. These findings indicate that anterior and posterior LIPC demonstrate distinct patterns of priming, with priming in the anterior region being task-specific, suggesting that this facilitation derives from repeated semantic processing of a stimulus.
以往的神经影像学研究表明，相对于初始（未启动）刺激处理，在重复（启动）刺激处理过程中，左侧前额叶下回（LIPC）的激活会减少。前额叶前部（大致为BA 45/47）和后部（大致为BA 44/6）LIPC激活的这些减少被解释为反映了对初始语义或语音处理的内隐记忆。然而，先前的研究并未明确表明LIPC启动效应特定于高级（语义和/或语音）而非低级（感知）过程的重现。此外，之前没有研究表明前额叶前部和后部LIPC区域的启动模式是可分离的。为了解决这些问题，本功能磁共振成像（fMRI）研究通过检查这些效应的任务特异性来探究LIPC中启动的本质。参与者最初以语义或非语义方式处理单词。随后，当参与者对先前以语义方式处理过的单词（任务内重复）、先前以非语义方式处理过的单词（跨任务重复）和先前未处理过的单词（新单词）做出语义决策时，对他们进行扫描。在行为上，观察到了任务特异性启动：对单词进行语义决策的反应时间在先前的语义处理后缩短，但在先前的非语义处理后没有缩短。前额叶前部LIPC的启动与这些结果相似，在任务内重复后观察到信号减少，但在跨任务重复后未观察到。重要的是，前额叶后部LIPC的神经启动表现出不同的模式：在任务内和跨任务重复后均观察到启动，任务内条件下的启动幅度往往更大。前额叶前部和后部LIPC区域之间的直接比较显示出显著的交互作用。这些发现表明，前额叶前部和后部LIPC表现出不同的启动模式，前部区域的启动具有任务特异性，这表明这种促进作用源于对刺激的重复语义处理。
