Ikeda H, Nishijo H, Miyamoto K, Tamura R, Endo S, Ono T
Department of Physiology, Faculty of Medicine, Toyama Medical and Pharmaceutical University, Japan.
Neuroscience. 1998 Jun;84(3):723-39. doi: 10.1016/s0306-4522(97)00569-1.
Current source generators (dipoles) of the human visual evoked potentials to pattern-onset stimuli were investigated with the dipole tracing method, using a realistic four-layer head model of scalp-skull-fluid-brain, which can equate the surface potential distributions on a scalp to one or two corresponding equivalent dipoles. Three healthy adult human subjects were used, and 29 electrodes were set on a scalp of each subject. Visual stimulus of a checkerboard pattern was presented for 250 ms in each of eight different visual fields (central and peripheral parts of each of four quadrant fields). The visual evoked potentials consisting of initial positive-late negative waves (CI and CII components designated by Jeffreys and Axford) were recorded mainly on the occipital region contralateral to stimulated visual fields. The initial positive wave (CI) of visual evoked potentials were divided into two components: early component of the CI (e-CI--an early small positive deflection with approximate peak latency of 70-90 ms) and late component of the CI (l-CI--a late large positive deflection with approximate peak latency of 100-120 ms). The dipole with a fit exceeding 98% dipolarity with our model at the shortest latencies was defined as an "earliest dipole" of the evoked potentials, produced by the primary responses in the occipital cortex to an afferent volley from the lateral geniculate body. These earliest dipoles, for eight different visual field stimulations, were estimated at the approximate peak of the e-CI. Estimated dipoles were superimposed on a three-dimensional magnetic resonance image of each subject's brain. Earliest dipoles for right upper and right lower quadrant-field stimulations were located at the left calcarine cortices below and above the calcarine fissure, respectively; earliest dipoles for left upper and left lower quadrant-field stimulations were located at the right calcarine cortices below and above the calcarine fissure, respectively. Furthermore, earliest dipoles for central and peripheral quadrant-field stimulations were located posteriorly and anteriorly in the calcarine cortex, respectively. The results from these non-invasive analyses of visual evoked potentials indicated topographic localization of the dipoles around the calcarine fissure based on the loci of the visual fields. This was comparable to the retinotopy of the human occipital lobe based on clinicopathological studies.
采用偶极子追踪法，利用头皮-颅骨-脑脊液-脑的逼真四层头部模型，研究了人类视觉诱发电位对模式起始刺激的电流源发生器（偶极子），该模型可将头皮上的表面电位分布等同于一个或两个相应的等效偶极子。使用了三名健康的成年人类受试者，在每个受试者的头皮上设置了29个电极。在八个不同视野（四个象限视野的中央和周边部分）中，每次呈现棋盘格图案的视觉刺激250毫秒。由初始正波-晚期负波（由杰弗里斯和阿克斯福德指定的CI和CII成分）组成的视觉诱发电位主要记录在受刺激视野对侧的枕区。视觉诱发电位的初始正波（CI）分为两个成分：CI的早期成分（e-CI——一个早期小正偏转，近似峰值潜伏期为70-90毫秒）和CI的晚期成分（l-CI——一个晚期大正偏转，近似峰值潜伏期为100-120毫秒）。在最短潜伏期与我们的模型偶极相关性超过98%的偶极子被定义为诱发电位的“最早偶极子”，由枕叶皮质对来自外侧膝状体传入冲动的初级反应产生。对于八种不同视野刺激的这些最早偶极子，估计在e-CI的近似峰值处。估计的偶极子叠加在每个受试者大脑的三维磁共振图像上。右上象限和右下象限视野刺激的最早偶极子分别位于距状裂下方和上方的左距状皮质；左上象限和左下象限视野刺激的最早偶极子分别位于距状裂下方和上方的右距状皮质。此外，中央象限和周边象限视野刺激的最早偶极子分别位于距状皮质的后部和前部。这些视觉诱发电位的非侵入性分析结果表明，基于视野位置，偶极子在距状裂周围的地形定位。这与基于临床病理研究的人类枕叶视网膜拓扑学相当。
