Syntactic functioning in non-language areas of the brain

論文發表人：詹曉蕙(亞利桑納大學語言學系博士班)

 

http://www.lsadc.org/info/pdf_files/2007_MeetingHandbook.pdf

 

大腦的演化，是從原始的「皮質下區域」──包含本研究所探討的基底神經節 (basal ganglia)──發展至具有高等認知功能的「新皮質」。由於人類在物種演化史上是最高等的生物，語言又為人類所獨有，因此幾乎所有從事語言研究的人都很自然地認為人類的新皮質就是語言的所在地。也因此，自1861年布洛卡(Broca)發現左腦第三腦回的損傷會導致語法缺失以來，許多繼之而起的語言研究，也就將重心放在新皮質，尤其是傳統的布洛卡語言區(Broca's area)；而皮質下區域也就一直被界定為僅具運動功能的原始區域。然而，愈來愈多的研究顯示，皮質下區域其實扮演了複雜的角色。以基底神經節為例，此區域可能負責與排序有關的認知功能。而對於帕金森症病人的研究更顯示，此腦區可能與語言的語句處理有著密切的關係。既然語句的產生是要將不同的詞組做一排序，向來被視為「非語言區」的基底神經節，也許在語句的排序上扮演著舉足輕重的角色。為解答此疑惑，本研究以功能性磁振造影觀察正常人在使用句法時這個腦區的活動情形。實驗結果顯示，基底神經節的尾核頭側以及布洛卡語言區在組成階層性句法結構的排序過程中，扮演了重要的角色。由於「階層性」被視為是人類語言迥異於其他動物溝通系統的分野，此發現推翻了基底神經節只是負責運動功能的想法，也進一步將傳統對於大腦語言表徵的論點，做一修正。

 

Decades of exploration in animals has led most language researchers to believe that syntax is unique to humans.  Great emphasis has been placed on the newly-evolved neocortex, especially language areas such as Broca's area, and the role that non-neocortex may play in language has been minimized, if not totally neglected.  However, recent studies show that Parkinson's disease patients have difficulty in sentence processing.  These patients' language areas are intact, but they have damage to their basal ganglia (BG)—non-neocortical brain structures subserving motor function.  If language is indeed a newly evolved feature of humans, the involvement of these "primitive" brain regions needs further exploration.  This project intends to use event-related functional Magnetic Resonance Imaging (fMRI) to study the involvement of the BG in language.  Previous research has demonstrated that the BG are implicated in building up sequences of behavior into meaningful, goal-directed repertoires.  We hypothesize that, since producing a sentence involves arranging syntactic constituents into a sequence that expresses the speaker's intention, the BG should be recruited during a sentence production task.  Our study demonstrates that the head of caudate nucleus (part of the BG), together with Broca's area, take part in the sequencing of hierarchical syntactic structure.  This finding suggests that language (or more specifically, sentence production) may share a common base with other non-linguistic functions, which may contribute to the hot debate on the (non)specificity of language.