Portin K, Hari R
Brain Research Unit, Helsinki University of Technology, Espoo, Finland.
Proc Biol Sci. 1999 May 22;266(1423):981-5. doi: 10.1098/rspb.1999.0733.
We studied visual representation in the parietal cortex by recording whole-scalp neuromagnetic responses to luminance stimuli of varying eccentricities. The stimuli were semicircles (5.5 degrees in radius) presented at horizontal eccentricities from 0 degree to 16 degrees, separately in the right and left hemifields. All stimuli evoked responses in the contralateral occipital and medial parietal areas. The waveforms and distributions of the occipital responses varied with stimulus side (left, right) and eccentricity, whereas the parietal responses were remarkably similar to all stimuli. The equivalent sources of the parietal signals clustered within 1 cm3 in the medial parieto-occipital sulcus and did not differ significantly between the stimuli. The strength of the parietal activation remained practically constant with increasing stimulus eccentricity, suggesting that the visual areas in the parieto-occipital sulcus lack the enhanced foveal representation typical of most other visual areas. This result strengthens our previous suggestion that the medial parieto-occipital sulcus is the human homologue of the monkey V6 complex, characterized by, for example, lack of retinotopy and the absence of relative foveal magnification.
我们通过记录全头皮对不同离心率的亮度刺激的神经磁反应，研究了顶叶皮质中的视觉表征。刺激物是半径为5.5度的半圆，分别在右半视野和左半视野中以从0度到16度的水平离心率呈现。所有刺激均在对侧枕叶和内侧顶叶区域诱发反应。枕叶反应的波形和分布随刺激侧（左、右）和离心率而变化，而顶叶反应对所有刺激都非常相似。顶叶信号的等效源聚集在内侧顶枕沟内1立方厘米的范围内，且不同刺激之间无显著差异。随着刺激离心率的增加，顶叶激活强度实际上保持不变，这表明顶枕沟中的视觉区域缺乏大多数其他视觉区域典型的增强的中央凹表征。这一结果强化了我们之前的观点，即内侧顶枕沟是猴子V6复合体在人类中的同源物，其特征例如缺乏视网膜拓扑结构和相对中央凹放大率的缺失。
