Gootjes L, Bouma A, Van Strien J W, Van Schijndel R, Barkhof F, Scheltens Ph
Department of Clinical Neuropsychology, Vrije Universiteit, Amsterdam, The Netherlands.
Neuropsychologia. 2006;44(2):208-17. doi: 10.1016/j.neuropsychologia.2005.05.002. Epub 2005 Jun 13.
Alzheimer's disease (AD) involves not only gray matter but also white matter pathology, as reflected by atrophy of the corpus callosum (CC). Since decreased CC size may indicate reduced functional interhemispheric connectivity, differences in callosal size may have cognitive consequences that may become specifically apparent in neuropsychological tasks that tap hemispheric laterality. In the present study, we examined callosal functioning with a dichotic listening task in 25 Alzheimer patients, 20 healthy elderly and 20 healthy elderly with subjective memory complaints. We found decreased performance, increased ear asymmetry, and decreased callosal size in the AD group compared to healthy elderly. As expected, in the healthy elderly, we found significant negative correlations between ear asymmetry and callosal size, specifically in the anterior and posterior callosal subareas. While the association with the posterior subareas (isthmus and splenium) points at involvement of temporal areas mediating language processing, the association with the anterior subarea (the rostrum and genu) points at involvement of frontal areas mediating attention and executive functions. Remarkably however, in contrast to the healthy elderly, callosal size was not related to ear asymmetry in the AD group. The absence of an association between callosal atrophy and ear asymmetry implies that other pathological processes, next to reduced callosal functioning, attribute to ear asymmetry in AD. Difficulties to attend specifically to the left ear during dichotic listening in some of the AD patients, points at decreased attention and executive functions and suggests that pathology of specifically the frontal areas is involved.
阿尔茨海默病（AD）不仅涉及灰质病变，还涉及白质病变，这在胼胝体（CC）萎缩中有所体现。由于CC尺寸减小可能表明半球间功能连接性降低，胼胝体大小的差异可能会产生认知后果，这在利用半球侧化的神经心理学任务中可能会特别明显。在本研究中，我们通过双耳分听任务对25名阿尔茨海默病患者、20名健康老年人和20名有主观记忆主诉的健康老年人的胼胝体功能进行了检测。我们发现，与健康老年人相比，AD组的表现下降、耳不对称性增加且胼胝体尺寸减小。正如预期的那样，在健康老年人中，我们发现耳不对称性与胼胝体大小之间存在显著的负相关，特别是在胼胝体的前、后亚区域。虽然与后亚区域（峡部和压部）的关联表明介导语言处理的颞叶区域受累，但与前亚区域（嘴部和膝部）的关联表明介导注意力和执行功能的额叶区域受累。然而，值得注意的是，与健康老年人不同，AD组的胼胝体大小与耳不对称性无关。胼胝体萎缩与耳不对称性之间缺乏关联意味着，除了胼胝体功能降低外，其他病理过程也导致了AD患者的耳不对称性。一些AD患者在双耳分听时难以特别关注左耳，这表明注意力和执行功能下降，并提示特别是额叶区域存在病变。
