Deshpande Gopikrishna, Wang Yun
AU MRI Research Center, Department of Electrical & Computer Engineering, Auburn University, Auburn, AL 36849, USA.
Department of Psychological Sciences, Auburn University, Auburn, AL 36849, USA.
Brain Sci. 2022 Oct 7;12(10):1361. doi: 10.3390/brainsci12101361.
Layer-specific cortical microcircuits have been explored through invasive animal studies, yet it is not possible to reliably characterize them functionally and noninvasively in the human brain. However, recent advances in ultra-high-field functional magnetic resonance imaging (fMRI) have made it feasible to reasonably resolve layer-specific fMRI signals with sub-millimeter resolution. Here, we propose an experimental and analytical framework that enables the noninvasive functional characterization of layer-specific cortical microcircuits. Specifically, we illustrate this framework by characterizing layer-specific functional pathways in the corticogeniculate network of the human visual system by obtaining sub-millimeter fMRI at 7T using a task which engages the magnocellular pathway between the lateral geniculate nucleus (LGN) and the primary visual cortex. Our results demonstrate that: (i) center-surround inhibition in magnocellular neurons within LGN is detectable using localized fMRI responses; (ii) feedforward (LGN → layers VI/IV, layer IV → layer VI) and feedback (layer VI → LGN) functional pathways, known to exist from invasive animal studies, can be inferred using dynamic directional connectivity models of fMRI and could potentially explain the mechanism underlying center-surround inhibition as well as gain control by layer VI in the human visual system. Our framework is domain-neutral and could potentially be employed to investigate the layer-specific cortical microcircuits in other systems related to cognition, memory and language.
特定层的皮质微回路已通过侵入性动物研究进行了探索，但在人类大脑中无法以功能和非侵入性方式可靠地表征它们。然而，超高场功能磁共振成像（fMRI）的最新进展使得以亚毫米分辨率合理解析特定层的fMRI信号成为可能。在这里，我们提出了一个实验和分析框架，能够对特定层的皮质微回路进行非侵入性功能表征。具体而言，我们通过在7T下使用一项涉及外侧膝状体核（LGN）和初级视觉皮层之间大细胞通路的任务获取亚毫米fMRI，来表征人类视觉系统皮质膝状体网络中特定层的功能通路，以此说明该框架。我们的结果表明：（i）使用局部fMRI反应可检测到LGN内大细胞神经元的中心-外周抑制；（ii）从侵入性动物研究中已知存在的前馈（LGN→VI/IV层、IV层→VI层）和反馈（VI层→LGN）功能通路，可以使用fMRI的动态方向连接模型推断出来，并且可能解释人类视觉系统中中心-外周抑制以及VI层增益控制的潜在机制。我们的框架是领域中立的，可能被用于研究与认知、记忆和语言相关的其他系统中的特定层皮质微回路。
