Depth-dependent fMRI: feasibility and utility

摘要 功能性磁共振成像（fMRI）无疑是神经科学家的主力， 想要对人类行为的神经关联进行局部测量。然而，最近的研究表明， fMRI结果与传统的侵入性（直接）神经电生理测量相冲突， 群体反应：注意力强烈调节初级视觉皮层（V1）的fMRI反应，但仅 弱调制神经放电率; V1的fMRI反应预测感知状态，而只有微妙的方面 V1神经反应的直接记录与感知相关。和解的重要一步 功能磁共振成像数据和侵入性电生理学之间的区别是获得功能磁共振成像数据，可以绘制出 局部神经群体的细节在更接近于由电极采样的尺度上编码。的 拟议的实验将使用7特斯拉的功能磁共振成像与亚毫米分辨率-一个空间尺度可比， 局部场电位的电生理学-以确定神经群体的空间细节 V1中的响应取决于视觉刺激特性以及感知状态。 由于输入、输出和本地连接是根据深度隔离的， 本研究旨在分离不同皮层深度的信号。最近的一些文献报告表明， 不同皮层深度的fMRI反应幅度不同。然而，尚未确定是否 深度依赖的fMRI实际上反映了不同皮层深度的局部神经网络变化。以下 旨在验证功能磁共振成像具有与神经活动有意义对应的不同层敏感性。 第一个目的是验证层特定的功能磁共振成像对固有神经网络的已知属性。 虽然fMRI和电生理测量V1反应调制由于行为或知觉 过程（假定的反馈过程）不同意，有充分的证据表明协议 功能磁共振成像和电生理学测量的内在神经反应，如对比敏感度， 或取向选择性。因此，两组实验将量化深度依赖的fMRI反应， 简单的视觉刺激，验证功能磁共振成像层状轮廓对层状轮廓预测的电生理学。 第二个目的是研究提取的视觉信息对V1神经反应的调制 在更大的空间尺度上。通过全局场景结构增强V1神经反应（图形/背景 分割）和通过均匀纹理（依赖于方向的环绕）抑制V1神经反应 抑制）在意识调节V1调制的作用方面有重要差异。我们将量化 在这两种不同的背景调制下的功能磁共振成像层状轮廓。因为这两种视觉特征 分组和同向抑制受到神经系统疾病如自闭症的影响， 精神分裂症，验证了一种用于监测这些视觉背景调制机制的技术， 在临床环境中的效用。

ABSTRACT Functional magnetic resonance imaging (fMRI) is undeniably the workhorse for neuroscientists who want localized measurements of neural correlates of human behavior. However, recent studies have presented fMRI results that conflict with traditional invasive (direct) electrophysiological measurements of neural population responses: attention strongly modulates the fMRI response in primary visual cortex (V1) but only weakly modulates neural firing rates; fMRI responses in V1 predict perceptual states while only subtle aspects of direct recordings of V1 neural responses correlate with perception. An important step toward reconciling the differences between fMRI data and invasive electrophysiology is to obtain fMRI data that can map out the details of the local neural population code on a scale that is closer to that sampled by electrodes. The proposed experiments will use 7 Tesla fMRI with sub-millimeter resolution – a spatial scale comparable to that of the local field potential in electrophysiology – to determine how the spatial details of the neural population response in V1 depend on visual stimulus properties as well as perceptual state. Because input, output and local connections are segregated according to depth, the primary focus of this research is to dissociate signals at different cortical depths. Several recent literature reports show that the fMRI response amplitude is different at different cortical depths. However, it is not yet established whether depth-dependent fMRI actually reflects local neural network changes at different cortical depths. The following aims seek to verify that fMRI has differential laminar sensitivity that corresponds meaningfully to neural activity. The first aim is to validate layer-specific fMRI against known properties of the intrinsic neural network. While fMRI and electrophysiological measurements of V1 response modulation due to behavioral or perceptual processes (putative feedback processes) disagree, there has been ample demonstration of the agreement between fMRI and electrophysiological measurements of intrinsic neural responses such as contrast sensitivity or orientation selectivity. Two sets of experiments will therefore quantify the depth-dependent fMRI response to simple visual stimuli, validating the fMRI laminar profile against laminar profiles predicted by electrophysiology. The second aim is to study modulation of neural responses in V1 by visual information that is extracted over a larger spatial scale. Enhancement of V1 neural responses by global scene structure (figure/ground segmentation) and suppression of V1 neural responses by uniform texture (orientation-dependent surround suppression) differ importantly in the role of awareness in regulating the modulation in V1. We will quantify fMRI laminar profiles under these two different kinds of contextual modulation. Because both visual feature grouping and iso-orientation suppression are affected by neurological disorders such as autism and schizophrenia, validating a technique for monitoring these mechanisms of visual contextual modulation has utility in the clinical setting.