Shepherd A J
School of Psychology, Birkbeck College, University of London, London, UK.
Brain. 2006 Jul;129(Pt 7):1833-43. doi: 10.1093/brain/awl124. Epub 2006 May 9.
Visual after-effects are illusions that occur after prolonged viewing of visual displays (pattern adaptation). The motion after-effect (MAE), for example, is an illusory impression of motion that is seen after viewing moving displays. After-effects have been used extensively in basic vision research as well as in clinical settings, and have been reported to be enhanced in migraine. Pattern adaptation is a cortical phenomenon that reflects both cellular mechanisms acting within individual neurons and specific interactions between groups of neurons activated by the adapting display. A remarkable feature of the MAE is that its duration is only slightly reduced if a delay is inserted between the end of the adaptation and the test display ('storage'). The reduction is consistent with recovery of the cellular component, and the residual with network changes that are maintained during the delay. This study aimed (i) to assess explanations for prolonged MAEs in migraine by teasing apart the proposed cellular and network components of adaptation using storage; (ii) to determine the extent of cortical abnormality in migraine using local and global MAEs, which reflect adaptation at different stages of the visual system. Fifty migraine (22 with, 28 without aura) and 50 control participants adapted to motion before viewing a stationary or dynamic (random motion) test, which consequently appeared to move in the opposite direction (local and global MAEs, respectively). Half of the trials included a delay between the adapting and test displays. The results extend those reported previously, as both local and global MAEs lasted longer in migraine compared with the control group. Global MAEs survived delays almost completely for both groups, whereas local MAEs were reduced to a greater extent in migraine. There were no significant differences between migraine subgroups classified according to the presence or absence of visual aura. These results suggest that cellular recovery is slowed in migraine for early but not later visual cortical areas. Sustained network changes following adaptation are implicated across cortical areas. Differences between people with and without migraine on various measures of visual perception have been attributed to abnormal cortical processing in migraine, variously described by hyperexcitability, heightened responsiveness and/or a lack of intra-cortical inhibition. The results are not consistent with hyperexcitability resulting from a lack of inhibition in migraine, but are consistent with extended suppression of intra-cortical excitation. The implications of these results for alternative models of hyperexcitability are discussed.
视觉后效是在长时间观看视觉显示（图案适应）后出现的错觉。例如，运动后效（MAE）是在观看运动显示后看到的一种虚幻的运动印象。后效已在基础视觉研究以及临床环境中广泛使用，并且据报道在偏头痛中会增强。图案适应是一种皮质现象，它反映了单个神经元内起作用的细胞机制以及由适应显示激活的神经元组之间的特定相互作用。MAE的一个显著特征是，如果在适应结束和测试显示（“存储”）之间插入延迟，其持续时间只会略有缩短。这种缩短与细胞成分的恢复一致，而残留部分与延迟期间维持的网络变化一致。本研究旨在：（i）通过使用存储来区分所提出的适应的细胞和网络成分，评估偏头痛中MAE延长的解释；（ii）使用局部和全局MAE来确定偏头痛中皮质异常的程度，这反映了视觉系统不同阶段的适应情况。50名偏头痛患者（22名有先兆，28名无先兆）和50名对照参与者在观看静止或动态（随机运动）测试之前适应运动，结果测试显示似乎向相反方向移动（分别为局部和全局MAE）。一半的试验在适应和测试显示之间包含延迟。结果扩展了先前报道的内容，因为与对照组相比，偏头痛患者的局部和全局MAE持续时间更长。两组的全局MAE在延迟后几乎完全保留，而偏头痛患者的局部MAE减少程度更大。根据是否有视觉先兆分类的偏头痛亚组之间没有显著差异。这些结果表明，偏头痛患者早期视觉皮质区域的细胞恢复减慢，但后期则不然。适应后持续的网络变化涉及整个皮质区域。有偏头痛和无偏头痛的人在各种视觉感知测量上的差异归因于偏头痛中异常的皮质处理，不同地描述为过度兴奋、反应性增强和/或缺乏皮质内抑制。结果与偏头痛中由于缺乏抑制导致的过度兴奋不一致，但与皮质内兴奋的延长抑制一致。讨论了这些结果对过度兴奋替代模型的影响。
