Parvocellular and magnocellular contributions to the initial generators of the visual evoked potential: High-density electrical mapping of the "C1" component
Parvocellular and magnocellular contributions to the initial generators of the visual evoked potential: High-density electrical mapping of the "C1" component
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DOI：
10.1007/s10548-008-0063-4
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发表时间：
2008-09-01
期刊：
影响因子：
2.7
通讯作者：
McCourt, Mark E.
中科院分区：
文献类型：
--
作者：
Foxe, John J.;Strugstad, E. Cathrine;McCourt, Mark E.
VEP的C1分量被认为是人类视觉皮层的视网膜定位区域（V1和V2）的初始传入的指标。C1起始于顶枕部头皮中央，在45和60 ms之间，峰值在70和100 ms之间，然后分解为以下P1分量。通过利用等亮度和低对比度亮度刺激，我们评估了大细胞（M）和小细胞（P）途径对C1生成的相对贡献。C1在100%亮度对比度条件下（刺激P和M通路）在88 ms时最大，在等亮度色度条件下（隔离P通路的贡献）在115 ms时最大。然而，在4%的亮度对比度条件下（隔离M通路），刺激仍然被清楚地感知，C1完全不存在。在这种低对比度条件下C1的缺失不太可能归因于缺乏刺激能量，因为诱发了强大的P1-N1复合体。因此，这些数据意味着，C1可能主要是小细胞起源。然而，这些数据并不排除M系统在较高对比度水平下的一些贡献。尽管如此，C1到P-隔离等亮度色刺激的幅度相当于由100%对比度刺激引起的幅度，这表明即使在高对比度水平下，P系统也是最大的贡献者。这些数据与猕猴的颅内记录有关，也表明当使用M偏置刺激时，IV层中的初始电流汇可能无法有效地传播到头皮表面。我们还讨论了如何这一发现有影响的长期传统的注意力研究，使用C1作为一个度量的初始V1传入人类。C1被反复询问潜在的选择性注意调制，特别是在空间注意设计中，前提是该组件的调制或缺乏，将是支持或反对视觉皮层初始输入选择的证据。鉴于这里的发现，我们敦促在解释C1效应时，考虑占主导地位的细胞贡献将是必要的。例如，空间注意机制可能主要通过M系统起作用，因此C1在此类研究中可能并不总是代表足够的依赖性测量。
The C1 component of the VEP is considered to index initial afference of retinotopic regions of human visual cortex (V1 and V2). C1 onsets over central parieto-occipital scalp between 45 and 60 ms, peaks between 70 and 100 ms, and then resolves into the following P1 component. By exploiting isoluminant and low-contrast luminance stimuli, we assessed the relative contributions of the Magnocellular (M) and Parvocellular (P) pathways to generation of C1. C1 was maximal at 88 ms in a 100% luminance contrast condition (which stimulates both P and M pathways) and at 115 ms in an isoluminant chromatic condition (which isolates contributions of the P pathway). However, in a 4% luminance contrast condition (which isolates the M pathway), where the stimuli were still clearly perceived, C1 was completely absent. Absence of C1 in this low contrast condition is unlikely to be attributable to lack of stimulus energy since a robust P1-N1 complex was evoked. These data therefore imply that C1 may be primarily parvocellular in origin. The data do not, however, rule out some contribution from the M system at higher contrast levels. Nonetheless, that the amplitude of C1 to P-isolating isoluminant chromatic stimuli is equivalent to that evoked by 100% contrast stimuli suggests that even at high contrast levels, the P system is the largest contributor. These data are related to intracranial recordings in macaque monkeys that have also suggested that the initial current sink in layer IV may not propagate effectively to the scalp surface when M-biased stimuli are used. We also discuss how this finding has implications for a long tradition of attention research that has used C1 as a metric of initial V1 afference in humans. C1 has been repeatedly interrogated for potential selective attentional modulations, particularly in spatial attentional designs, under the premise that modulation of this component, or lack thereof, would be evidence for or against selection at the initial inputs to visual cortex. Given the findings here, we would urge that in interpreting C1 effects, a consideration of the dominant cellular contributions will be necessary. For example, it is plausible that spatial attention mechanisms could operate primarily through the M system and that as such C1 may not always represent an adequate dependent measure in such studies.