Mentis M J, Horwitz B, Grady C L, Alexander G E, VanMeter J W, Maisog J M, Pietrini P, Schapiro M B, Rapoport S I
Laboratory of Neurosciences, National Institute on Aging, NIH, Bethesda, MD 20892, USA.
Am J Psychiatry. 1996 Jan;153(1):32-40. doi: 10.1176/ajp.153.1.32.
Visual-processing abnormalities commonly contribute to typical Alzheimer's disease symptoms, but their detailed pathophysiology remains unknown. To investigate why patients with Alzheimer's disease have greater difficulty performing visuoconstructive (magnocellular-dominated) tasks than face- or color-perception (parvocellular-dominated) tasks, the authors measured brain activation in response to a temporally graded visual stimulus (neural stress test) during positron emission tomography.
The stress test measured regional cerebral blood flow (CBF) in response to a patterned flash stimulus in the resting state (0 Hz in the dark) and at frequencies of 1, 2, 4, 7, and 14 Hz. Ten patients with Alzheimer's disease and 12 age- and sex-matched comparison subjects were studied.
The striate response at 7 Hz and 14 Hz (the degree of regional CBF increase from that at 0 Hz) was significantly less in the patients than in the comparison subjects, whereas the change in regional CBF at the lower frequencies did not differ between groups. In bilateral middle temporal association areas activated by motion and dominated by magnocellular input, regional CBF at 1 Hz (the frequency with maximal apparent motion) was significantly greater than at 0 Hz in the comparison subjects but not in the patients.
The magnocellular visual system normally responds to high-frequency input and motion; the failure of response in the striate cortex at high but not low frequencies in the Alzheimer's patients suggests greater magnocellular than parvocellular dysfunction at these levels. Activation failure in the middle temporal areas in the patients supports magnocellular dysfunction. The finding that the Alzheimer's disease group had abnormal visual cortical function emphasizes the importance of clinical visuospatial evaluation of patients with Alzheimer's disease to fully understand symptom production and to plan interventions.
视觉处理异常通常会导致典型的阿尔茨海默病症状，但其详细的病理生理学仍不清楚。为了研究为什么阿尔茨海默病患者在执行视觉建构（以大细胞为主）任务时比面部或颜色感知（以小细胞为主）任务更困难，作者在正电子发射断层扫描期间测量了对时间分级视觉刺激（神经应激测试）的脑激活情况。
应激测试测量了静息状态（黑暗中0Hz）以及1、2、4、7和14Hz频率下对图案闪光刺激的局部脑血流量（CBF）。研究了10名阿尔茨海默病患者和12名年龄及性别匹配的对照受试者。
患者在7Hz和14Hz时的纹状反应（局部CBF相对于0Hz时的增加程度）明显低于对照受试者，而低频时局部CBF的变化在两组之间没有差异。在由运动激活并以大细胞输入为主的双侧颞中联合区域，1Hz（最大明显运动频率）时的局部CBF在对照受试者中明显高于0Hz，但在患者中并非如此。
大细胞视觉系统通常对高频输入和运动做出反应；阿尔茨海默病患者在高频而非低频时纹状皮质反应失败，表明在这些水平上大细胞功能障碍比小细胞更严重。患者颞中区域的激活失败支持大细胞功能障碍。阿尔茨海默病组存在视觉皮质功能异常这一发现强调了对阿尔茨海默病患者进行临床视觉空间评估对于全面理解症状产生和规划干预措施的重要性。
