Center for Neuroscience Imaging Research (CNIR), Institute for Basic Science (IBS), Suwon 16419, Republic of Korea; Department of Biomedical Engineering, Sungkyunkwan University, Suwon 16419, Republic of Korea.
Center for Neuroscience Imaging Research (CNIR), Institute for Basic Science (IBS), Suwon 16419, Republic of Korea.
Neuroimage. 2021 Feb 1;226:117542. doi: 10.1016/j.neuroimage.2020.117542. Epub 2020 Nov 10.
The functional characteristics of the mouse visual system have not previously been well explored using fMRI. In this research, we examined 9.4 T BOLD fMRI responses to visual stimuli of varying pulse durations (1 - 50 ms) and temporal frequencies (1 - 10 Hz) under ketamine and xylazine anesthesia, and compared fMRI responses of anesthetized and awake mice. Under anesthesia, significant positive BOLD responses were detected bilaterally in the major structures of the visual pathways, including the dorsal lateral geniculate nuclei, superior colliculus, lateral posterior nucleus of thalamus, primary visual area, and higher-order visual area. BOLD responses increased slightly with pulse duration, were maximal at 3 - 5 Hz stimulation, and significantly decreased at 10 Hz, which were all consistent with previous neurophysiological findings. When the mice were awake, the BOLD fMRI response was faster in all active regions and stronger in the subcortical areas compared with the anesthesia condition. In the V1, the BOLD response was biphasic for 5 Hz stimulation and negative for 10 Hz stimulation under wakefulness, whereas prolonged positive BOLD responses were observed at both frequencies under anesthesia. Unexpected activation was detected in the extrastriate postrhinal area and non-visual subiculum complex under anesthesia, but not under wakefulness. Widespread positive BOLD activity under anesthesia likely results from the disinhibition and sensitization of excitatory neurons induced by ketamine. Overall, fMRI can be a viable tool for mapping brain-wide functional networks.
先前，使用 fMRI 尚未很好地探索小鼠视觉系统的功能特征。在这项研究中，我们在氯胺酮和甲苯噻嗪麻醉下检查了不同脉冲持续时间（1-50ms）和时间频率（1-10Hz）的视觉刺激对 BOLD fMRI 反应，并比较了麻醉和清醒小鼠的 fMRI 反应。在麻醉下，双侧视觉通路的主要结构（包括背外侧膝状体核、上丘、丘脑外侧后核、初级视觉区和高级视觉区）均检测到明显的正 BOLD 反应。BOLD 反应随脉冲持续时间略有增加，在 3-5Hz 刺激时达到最大值，在 10Hz 时显著降低，这与以前的神经生理学发现一致。当小鼠清醒时，与麻醉状态相比，所有活跃区域的 BOLD fMRI 反应更快，皮质下区域的反应更强。在 V1 中，5Hz 刺激时 BOLD 反应呈双相，10Hz 刺激时呈负相，而麻醉时在这两种频率下均观察到延长的正 BOLD 反应。在麻醉下检测到意外激活的外侧后穹窿区和非视觉海马复合体，但在清醒时则没有。麻醉下广泛的正 BOLD 活性可能是由于氯胺酮诱导的兴奋性神经元去抑制和敏化所致。总的来说，fMRI 可以成为绘制全脑功能网络的可行工具。
