Brain dynamics of lexical selection in speech production

描述（由申请人提供）：在正常语言中，成年人从不少于5万至10万个心理词汇中选择常用词汇，每秒流畅地说出2至3个单词。词汇选择是我们在言语中选择合适的词的过程，是语言产生的核心过程。在某种程度上，所有失语患者都观察到词法选择的病理性破坏（即异常），也可能存在于神经退行性疾病和正常衰老中。尽管词汇选择对语言至关重要，并且由于词汇选择的中断造成了巨大的个人和社会成本，但人们对词汇选择的神经基础及其恢复过程知之甚少。前额叶皮层（PFC）和左颞叶皮层（LTC）的不同区域与词汇选择有关，但它们的确切作用以及它们相互作用以实现词汇选择和补偿的方式仍不清楚。这种知识的缺乏既有方法学上的原因，也有理论上的原因：(a)通常用于研究健康说话者的脑成像技术不能提供涉及词汇选择的大脑区域的时间信息。了解这些不同的区域在词汇加工过程中何时联机，可以确认它们的不同作用，也可以提示它们如何相互作用以实现词汇加工。(b)通常将语言与其他认知功能分开考虑。越来越多的证据表明，词汇选择依赖于领域一般认知控制机制。如果这是真的，那就意味着不同的大脑

DESCRIPTION (provided by applicant): In normal speech, adults fluidly utter 2 to 3 words per second selected from no less than 50,000 to 100,000 regularly-used words in the mental lexicon. Lexical selection is the process by which we access and fit an appropriate word to ongoing speech and is a core process for language production. Pathological disruption of lexical selection (i.e., anomia) is observed to some extent in all aphasic patients and can also be present in neurodegenerative diseases as well as normal aging. Despite the central importance of lexical selection to language and the immense personal and societal cost caused by its disruption, its neural basis and that involved in its recovery are poorly understood. Different regions of the prefrontal cortex (PFC) and of the left temporal cortex (LTC) have been associated with lexical selection but their precise role and the way they interact to enable lexica selection and compensation are still unknown. This lack of knowledge has both methodological and theoretical causes: (a) The brain imaging techniques generally used to study healthy speakers do not provide temporal information on the brain regions that are involved in lexical selection. Knowing when these different regions come online during lexical processing would confirm their different roles and would also suggest how they interact with each other to achieve lexical processing. (b) Language has typically been considered in isolation from other cognitive functions. A burgeoning body of evidence suggests that lexical selection is dependent on domain-general cognitive control mechanisms. If this is true, it would suggest that different brain regions play different linguistic and non-linguistic roles, a finding that would have significant ramifications for treatment and recovery of brain-injured patients. The goal of the proposed research is to test the hypotheses that: (1) Lexical selection is supported by top-down modulations from the left PFC onto the left LTC, similar to how non-linguistic action selection is controlled, and (2) The right PFC serves as a compensatory top-down mechanism for lexical selection when the left PFC is injured, similar to what has been shown outside of the language domain. To test these hypotheses, a combination of novel theoretical and methodological approaches will be used. First, the unique opportunity to record electrocorticography (ECoG) in neurosurgical patients will be used to determine which, when and how subregions of the PFC and the LTC are involved in lexical selection. Second, linguistic vs. domain-general contributions to lexical processing will be tested by directly comparing patients' performance on two tasks using the same stimuli, but differing only in the type of stimulus-response associations to be performed (linguistic vs. domain-general). Finally, these same tasks will be used with neurological patients recovering from stroke in either the left or right PFC in order to determine the effects of these injuries on lexical selection. Behavioral measurements as well as surface EEG signals will determine the relative roles of these regions in lexical selection, and whether the right PFC participates in compensating for the loss of top-down control when the left PFC is injured.