Attention mechanisms at different cortical layers of human visual cortex remain poorly understood. Using submillimeter-resolution fMRI at 7 T, we investigated the effects of top-down spatial attention on the contrast responses across different cortical depths in human early visual cortex. Gradient echo (GE) T2* weighted BOLD signal showed an additive effect of attention on contrast responses across cortical depths. Compared to the middle cortical depth, attention modulation was stronger in the superficial and deep depths of V1, and also stronger in the superficial depth of V2 and V3. Using ultra-high resolution (0.3 mm in-plane) balanced steady-state free precession (bSSFP) fMRI, a multiplicative scaling effect of attention was found in the superficial and deep layers, but not in the middle layer of V1. Attention modulation of low contrast response was strongest in the middle cortical depths, indicating baseline enhancement or contrast gain of attention modulation on feedforward input. Finally, the additive vs. scaling effect of attention from GE-EPI and bSSFP signals can be explained by stronger nonlinearity of BOLD signals from large than small blood vessels, suggesting multiplicative effect of attention on neural activity. These findings support that top-down spatial attention mainly operates through feedback connections from higher order cortical areas, and a distinct mechanism of attention may also be associated with feedforward input through subcortical pathway.

Highlights

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Response or activity gain of spatial attention in superficial and deep layers

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Contrast gain or baseline shift of attention in V1 middle layer

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Nonlinearity of large blood vessel causes additive effect of attention on T2*w BOLD

人类视觉皮层不同皮质层的注意机制仍然知之甚少。使用 7 T 的亚毫米分辨率 fMRI，我们研究了自上而下的空间注意力对人类早期视觉皮层不同皮层深度的对比反应的影响。梯度回波 (GE) T2* 加权粗体信号显示了注意力对皮质深度对比度反应的附加效应。与中皮层深度相比，V1 浅层和深层的注意力调节更强，V2 和 V3 的浅层深度也更强。使用超高分辨率（0.3 mm 平面内）平衡稳态自由进动 (bSSFP) fMRI，在 V1 的浅层和深层发现了注意力的乘法缩放效应，但在 V1 的中间层没有发现。低对比度响应的注意力调制在中间皮层深度最强，表明前馈输入上注意力调制的基线增强或对比度增益。最后，来自 GE-EPI 和 bSSFP 信号的注意力的加性与缩放效应可以通过来自大血管的 BOLD 信号的更强非线性来解释，这表明注意力对神经活动的乘法效应。这些发现支持自上而下的空间注意力主要通过来自高阶皮层区域的反馈连接起作用，并且一种独特的注意力机制也可能与通过皮层下通路的前馈输入有关。来自 GE-EPI 和 bSSFP 信号的注意力的缩放效应可以通过来自大血管的 BOLD 信号的更强非线性来解释，这表明注意力对神经活动的乘法效应。这些发现支持自上而下的空间注意力主要通过来自高阶皮层区域的反馈连接起作用，并且一种独特的注意力机制也可能与通过皮层下通路的前馈输入有关。来自 GE-EPI 和 bSSFP 信号的注意力的缩放效应可以通过来自大血管的 BOLD 信号的更强非线性来解释，这表明注意力对神经活动的乘法效应。这些发现支持自上而下的空间注意力主要通过来自高阶皮层区域的反馈连接起作用，并且一种独特的注意力机制也可能与通过皮层下通路的前馈输入有关。

强调

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浅层和深层空间注意力的反应或活动增益

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V1中间层注意力的对比增益或基线偏移

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大血管的非线性导致注意力对 T2*w BOLD 的累加效应