Functional MRI of the Brain Centre, Nuffield Department of Clinical Neurosciences, John Radcliffe Hospital, Oxford OX3 9DU, United Kingdom.
J Neurosci. 2013 Jul 31;33(31):12779-91. doi: 10.1523/JNEUROSCI.4853-12.2013.
Loss of shape recognition in visual-form agnosia occurs without equivalent losses in the use of vision to guide actions, providing support for the hypothesis of two visual systems (for "perception" and "action"). The human individual DF received a toxic exposure to carbon monoxide some years ago, which resulted in a persisting visual-form agnosia that has been extensively characterized at the behavioral level. We conducted a detailed high-resolution MRI study of DF's cortex, combining structural and functional measurements. We present the first accurate quantification of the changes in thickness across DF's occipital cortex, finding the most substantial loss in the lateral occipital cortex (LOC). There are reduced white matter connections between LOC and other areas. Functional measures show pockets of activity that survive within structurally damaged areas. The topographic mapping of visual areas showed that ordered retinotopic maps were evident for DF in the ventral portions of visual cortical areas V1, V2, V3, and hV4. Although V1 shows evidence of topographic order in its dorsal portion, such maps could not be found in the dorsal parts of V2 and V3. We conclude that it is not possible to understand fully the deficits in object perception in visual-form agnosia without the exploitation of both structural and functional measurements. Our results also highlight for DF the cortical routes through which visual information is able to pass to support her well-documented abilities to use visual information to guide actions.
在视觉形态失认症中，形状识别丧失而使用视觉来指导行动的能力并未受到同等影响，这为两个视觉系统（用于“感知”和“行动”）的假说提供了支持。个体 DF 曾因多年前一氧化碳中毒而导致持续性视觉形态失认症，其行为水平的特征已得到广泛描述。我们对 DF 的大脑皮层进行了详细的高分辨率 MRI 研究，结合了结构和功能测量。我们首次对 DF 枕叶皮层的厚度变化进行了精确的量化，发现外侧枕叶皮层（LOC）的损失最大。LOC 与其他区域之间的白质连接减少。功能测量显示，在结构受损区域内存在活动的“口袋”。视觉区域的地形映射显示，DF 的 V1、V2、V3 和 hV4 等视觉皮质区域的腹侧部分存在有序的视网膜映射。尽管 V1 的背侧部分显示出地形顺序的证据，但在 V2 和 V3 的背侧部分无法找到这样的地图。我们得出的结论是，如果不利用结构和功能测量，就不可能完全理解视觉形态失认症中物体感知的缺陷。我们的结果还突出了 DF 大脑皮层的信息传递途径，这些途径能够传递视觉信息，以支持她有充分记录的使用视觉信息来指导行动的能力。
