Helenius P, Salmelin R, Service E, Connolly J F
Low Temperature Laboratory, Helsinki University of Technology, PO Box 2200, 02015 HUT, Espoo, FINLAND.
J Cogn Neurosci. 1999 Sep;11(5):535-50. doi: 10.1162/089892999563599.
The combined temporal and spatial resolution of MEG (magnetoencephalography) was used to study whether the same brain areas are similarly engaged in reading comprehension in normal and developmentally dyslexic adults. To extract a semantically sensitive stage of brain activation we manipulated the appropriateness of sentence-ending words to the preceding sentence context. Sentences, presented visually one word at a time, either ended with a word that was (1) expected, (2) semantically appropriate but unexpected, (3) semantically anomalous but sharing the initial letters with the expected word, or (4) both semantically and orthographically inappropriate to the sentence context. In both subject groups all but the highly expected sentence endings evoked strong cortical responses, localized most consistently in the left superior temporal cortex, although additional sources were occasionally found in more posterior parietal and temporal areas and in the right hemisphere. Thus, no significant differences were found in the spatial distribution of brain areas involved in semantic processing between fluent and dyslexic readers. However, both timing and strength of activation clearly differed between the two groups. First, activation sensitivity to word meaning within a sentence context began about 100 msec later in dyslexic than in control subjects. This is likely to result from affected presemantic processing stages in dyslexic readers. Second, the neural responses were significantly weaker in dyslexic than in control subjects, indicating involvement of a smaller or less-synchronous neural population in reading comprehension. Third, in contrast to control subjects, the dyslexic readers showed significantly weaker activation to semantically inappropriate words that began with the same letters as the most expected word than to both orthographically and semantically inappropriate sentence-ending words. Thus, word recognition by the dyslexic group seemed to be qualitatively different: Whereas control subjects perceived words as wholes, dyslexic subjects may have relied on sublexical word recognition and occasionally mistook a correctly beginning word for the one they had expected.
利用脑磁图（MEG）的时间和空间分辨率相结合的方法，研究正常成年人与发育性阅读障碍成年人在阅读理解过程中，相同脑区的参与情况是否相似。为了提取对语义敏感的脑激活阶段，我们操纵句子结尾单词与前文语境的匹配程度。句子以每次一个单词的方式视觉呈现，其结尾单词要么是（1）预期的，（2）语义合适但未预期的，（3）语义异常但与预期单词首字母相同的，要么是（4）在语义和正字法上均与句子语境不匹配的。在两个受试组中，除了高度预期的句子结尾外，其他所有结尾都引发了强烈的皮层反应，最一致地定位在左侧颞上叶皮层，尽管偶尔在更靠后的顶叶和颞叶区域以及右半球也发现了其他来源。因此，在流畅阅读者和阅读障碍者之间，参与语义处理的脑区空间分布没有显著差异。然而，两组在激活的时间和强度上明显不同。首先，阅读障碍者在句子语境中对单词意义的激活敏感性比对照组大约晚100毫秒开始。这可能是由于阅读障碍者的前语义处理阶段受到影响。其次，阅读障碍者的神经反应明显比对照组弱，表明参与阅读理解的神经群体规模较小或同步性较差。第三，与对照组不同，阅读障碍者对与最预期单词首字母相同但语义不适当的单词的激活，比对正字法和语义均不适当的句子结尾单词的激活明显更弱。因此，阅读障碍组的单词识别在性质上似乎有所不同：对照组将单词作为一个整体来感知，而阅读障碍者可能依赖于次词汇水平的单词识别，偶尔会将开头正确的单词误认为是他们预期的单词。
