Verstichel P, Cambier J
Clinique Neurologique, Hôpital Beaujon, Clichy.
Rev Neurol (Paris). 1997 Oct;153(10):561-8.
We describe two patients suffering from a letter-by-letter reading following an infarct in the left posterior cerebral artery's territory. Unlike most of the verbal alexics, this strategy was particularly fast and effective. Two other features distinguished these patients from verbal alexics: the absence of hemianopia and the sparing of the corpus callosum. A study of the reading of letters and words by each hemisphere was performed. In the first case, the left hemisphere was unable to identify any letter or word. The visual stimuli did not activate the visual word form, not the system which normally recognize letters. However, this latter could be activated by the information transmitted by the right hemisphere via the corpus callosum. In the second case, the left hemisphere could, as well as the right one, identify all the letters. On the other hand, identification of words was impaired, and did not improve when the duration of the visual presentation increased. The left hemisphere, unable to access to the visual word form, could not decipher letter-by-letter. One hypothesis is that the left visual working memory was reduced, and could not store more than one letter. The right hemisphere deciphered the words sequentially, and transmitted the information to the left systems which recognize the letter. These two observations confirm that letter-by-letter alexia could result exclusively from the destruction, of the inaccessibility of the visual word-form. A lesion of the left ventral occipito-temporal structures is sufficient, and a left hemianopia, or a splenial lesion is not absolutely necessary. The sparing of the corpus callosum allows a fast transmission to the left phonological processing, if the left systems recognizing letters are efficient.
我们描述了两名在左大脑后动脉供血区域梗死之后出现逐字母阅读情况的患者。与大多数言语性失读症患者不同，这种策略特别快速且有效。这两名患者与言语性失读症患者的另外两个区别在于：没有偏盲以及胼胝体未受损害。对每个半球的字母和单词阅读情况进行了研究。在第一个病例中，左半球无法识别任何字母或单词。视觉刺激未激活视觉词形，也未激活正常识别字母的系统。然而，后者可被右半球通过胼胝体传递的信息激活。在第二个病例中，左半球和右半球一样能够识别所有字母。另一方面，单词识别受损，并且当视觉呈现时间增加时也没有改善。左半球无法获取视觉词形，无法逐字母解读。一种假设是左视觉工作记忆减退，无法存储多于一个字母。右半球依次解读单词，并将信息传递给识别字母的左脑系统。这两项观察结果证实，逐字母失读症可能完全是由于视觉词形的破坏或无法获取所致。左枕颞腹侧结构的损伤就足够了，左偏盲或胼胝体损伤并非绝对必要。如果识别字母的左脑系统有效，胼胝体未受损害可使信息快速传递至左音韵处理系统。
