Saint Petersburg State University, Saint Petersburg, Russian Federation.
PLoS One. 2011;6(8):e22999. doi: 10.1371/journal.pone.0022999. Epub 2011 Aug 10.
Memory traces for words are frequently conceptualized neurobiologically as networks of neurons interconnected via reciprocal links developed through associative learning in the process of language acquisition. Neurophysiological reflection of activation of such memory traces has been reported using the mismatch negativity brain potential (MMN), which demonstrates an enhanced response to meaningful words over meaningless items. This enhancement is believed to be generated by the activation of strongly intraconnected long-term memory circuits for words that can be automatically triggered by spoken linguistic input and that are absent for unfamiliar phonological stimuli. This conceptual framework critically predicts different amounts of activation depending on the strength of the word's lexical representation in the brain. The frequent use of words should lead to more strongly connected representations, whereas less frequent items would be associated with more weakly linked circuits. A word with higher frequency of occurrence in the subject's language should therefore lead to a more pronounced lexical MMN response than its low-frequency counterpart. We tested this prediction by comparing the event-related potentials elicited by low- and high-frequency words in a passive oddball paradigm; physical stimulus contrasts were kept identical. We found that, consistent with our prediction, presenting the high-frequency stimulus led to a significantly more pronounced MMN response relative to the low-frequency one, a finding that is highly similar to previously reported MMN enhancement to words over meaningless pseudowords. Furthermore, activation elicited by the higher-frequency word peaked earlier relative to low-frequency one, suggesting more rapid access to frequently used lexical entries. These results lend further support to the above view on word memory traces as strongly connected assemblies of neurons. The speed and magnitude of their activation appears to be linked to the strength of internal connections in a memory circuit, which is in turn determined by the everyday use of language elements.
记忆痕迹通常被概念化为通过语言习得过程中的联想学习而发展起来的神经元相互连接的网络。这种记忆痕迹的激活在神经生理学上的反映是通过失匹配负波（MMN）来报告的，它表明对有意义的单词的反应比对无意义的项目的反应更强。这种增强被认为是由强烈的、相互连接的长期记忆回路的激活产生的，这些回路可以被语言输入自动触发，而对于不熟悉的语音刺激则不存在。这种概念框架批判性地预测了不同的激活量，这取决于大脑中单词的词汇代表的强度。频繁使用的单词应该会导致更紧密的连接表示，而不那么频繁的项目则与更弱的连接电路相关联。因此，在受试者的语言中出现频率较高的单词应该会导致更明显的词汇 MMN 反应，而不是其低频对应物。我们通过在被动的Oddball 范式中比较低频和高频单词诱发的事件相关电位来检验这一预测；物理刺激对比保持相同。我们发现，与我们的预测一致，呈现高频刺激相对于低频刺激会导致更明显的 MMN 反应，这一发现与先前报道的对有意义的单词相对于无意义的伪词的 MMN 增强非常相似。此外，高频单词诱发的激活比低频单词更早达到峰值，这表明对经常使用的词汇条目有更快的访问。这些结果进一步支持了上述关于单词记忆痕迹的观点，即它们是神经元之间强烈连接的集合。它们的激活速度和幅度似乎与记忆回路中内部连接的强度有关，而内部连接的强度又取决于语言元素的日常使用。
