The Neural Basis of Functional MRI Responses

功能性 MRI 反应的神经基础

• 批准号: 8158145
• 负责人: David A Leopold
• 金额: $ 44.31万
• 依托单位: NATIONAL INSTITUTE OF MENTAL HEALTH
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/8158145
• 关键词: Functional Magnetic Resonance Imaging; base; relating to nervous system; response

The Intramural Reseaerch Program at the NIMH is one of only a handful of sites in the world in which neural activity can be compared directly with simultaneously and/or sequentially recorded fMRI signals. We have integrated electrophysiology and imaging in alert, behaving monkeys by collaborating with the Neurophysiology Imaging Facility, a shared imaging facility dedicated to structural and functional brain imaging in nonhuman primates. In previous work, we have explored the relationship between neural signals and fMRI in the primary visual cortex of monkeys. Last year we published a study that for the first time identified specific conditions under which the two signals diverged. While fMRI and neural signals were normally in perfect sync, we showed that they behaved very differently during perceptual suppression, where a stimulus was seen but not perceived. This finding is an important link toward interpreting the results of many human neuroimaging studies that seem to disagree with electrophysiological recordings. In the last few months, we published a study investigating the neural basis of the resting-state fMRI signal. This signal, corresponding to the spontaneous, endogenous fMRI fluctuations that occur in the brain when a subject is not performing any explicit behavior, is studied widely in the human brain by hundreds of laboratories. It is of great interest because the statistical relationship of spontaneous fluctuations measured at different points in the brain carries information about the brains functional processing, a phenomenon termed functional connectivity. We were interested in the neural underpinnings of this phenomenon, and therefore performed simultaneous electrophysiological and fMRI measurements in awake monkeys. Surprisingly, we found that not only is the electrical activity of the cerebral cortex correlated with specific functional circuits, it is also correlated with activity over large swathes of the cortex. This nearly global span of signal fluctuations is an important aspect of brain activity that has been ignored, literally discarded, by the human neuroimaging community as noise. Our findings suggest that it is not noise, but may, in fact, represent that aspect of brain function that accounts for its highest fraction of metabolic consumption. These findings will influence the manner in which the human neuroimaging community considers and treats the global fMRI signal measured during the resting state. In a second, ongoing project, we have measured fMRI signals following focal brain injury. Specifically, we made targeted ablations in the primary visual cortex (V1) of nonhuman primates, and then observed the extent to which fMRI responses in areas receiving input from V1 reemerged after several weeks. We are particularly interested in whether the recovery of the fMRI signal shows the same properties, including the basic recovery time course, as the responses of single neurons measured in the same part of the brain. This approach therefore requires the careful coordination of fMRI, ablation, and electrode implantation. This three-pronged approach is then combined with behavior, asking the animal to tell us when they detect a visual target, to determine how the neural and fMRI signals related to one another, and how they further relate to perception. As a final portion of this project, we have investigated the neural pathways by which information may bypass the primary visual cortex. This was achieved by blocking electrical activity in an intermediate, relay nucleus, and then using fMRI to measure responses. Some of these results, which outline an important pathway mediating V1-independent vision, were recently published.

NIMH上的壁内复位程序是世界上仅有的少数几个站点之一，可以直接将神经活动与同时和/或顺序记录的fMRI信号进行比较。 我们已经将电生理学和成像整合在警觉中，通过与神经生理成像设施合作来表现猴子，这是一种共享成像设施，该设施致力于非人类灵长类动物的结构和功能性脑成像。 在先前的工作中，我们探索了猴子主要视觉皮层中神经信号与fMRI之间的关系。 去年，我们发表了一项研究，该研究首次确定了两个信号分歧的特定条件。 尽管fMRI和神经信号通常是完美同步的，但我们表明它们在感知抑制过程中的行为却大不相同，在感知抑制中，看到刺激但没有感知。 这一发现是解释许多人类神经影像学研究结果的重要联系，这些研究似乎不同意电生理记录。 在过去的几个月中，我们发表了一项研究，研究了静止状态fMRI信号的神经基础。 该信号与数百个实验室在人类大脑中广泛研究了受试者没有执行任何明确行为时在大脑中发生的自发的内源性FMRI波动。 这引起了人们的极大兴趣，因为在大脑不同点测量的自发波动的统计关系传递了有关大脑功能处理的信息，这是一种称为功能连接的现象。 我们对这种现象的神经基础感兴趣，因此在清醒猴子中同时进行了电生理和fMRI测量。令人惊讶的是，我们发现，不仅大脑皮质的电活动与特定的功能电路相关，而且还与大型皮质叶片上的活性相关。 这种几乎全球的信号波动跨度是大脑活动的重要方面，它被人类神经影像社区作为噪音忽略了，从字面上却丢弃了。 我们的发现表明，这不是噪音，但实际上可能代表了大脑功能的一方，这是其代谢消耗最高的最高分数。 这些发现将影响人类神经影像社区考虑并处理在静止状态下测得的全球fMRI信号的方式。 在第二个正在进行的项目中，我们测量了局灶性脑损伤后的fMRI信号。 具体而言，我们在非人类灵长类动物的主要视觉皮层（V1）中进行了靶向消融，然后观察了几周后从V1接收输入的区域中fMRI响应的程度。 我们对fMRI信号的恢复是否表现出相同的特性，包括基本恢复时间过程，这特别感兴趣，因为基本恢复时间过程是在大脑同一部分测得的单个神经元的响应。 因此，这种方法需要仔细协调fMRI，消融和电极植入。 然后将这种三管齐下的方法与行为结合在一起，要求动物告诉我们何时检测到视觉目标，以确定神经和fMRI信号如何相互关联，以及它们如何进一步与知觉相关。 作为该项目的最后一部分，我们研究了信息可以绕过主要视觉皮层的神经途径。 这是通过阻止中间，继电器核中的电活动，然后使用fMRI测量反应来实现的。 这些结果中有一些概述了介导V1独立视觉的重要途径。