Depth-dependent fMRI: feasibility and utility

摘要 不可否认，功能磁共振成像(FMRI)是神经科学家的主力 希望对人类行为的神经关联进行本地化测量。然而，最近的研究表明 FMRI结果与传统的有创(直接)神经电生理测量相冲突 群体反应：注意强烈地调节初级视觉皮质(V1)的fMRI反应，但仅限于 弱调节神经放电频率；V1中的fMRI反应预测感知状态，而只预测微妙的方面 V1神经反应的直接记录与知觉相关。朝着和解的重要一步 功能磁共振成像数据与有创电生理的区别在于，获得的功能磁共振数据可以绘制出 局部神经种群编码的细节在一个更接近于电极采样的尺度上。这个 拟议的实验将使用7特斯拉亚毫米分辨率的功能磁共振成像-空间尺度与 电生理学中的局部场势--以确定神经种群的空间细节如何 V1中的反应取决于视觉刺激特性和知觉状态。 由于输入、输出和本地连接是根据深度分离的，因此 这项研究是为了分离不同皮质深度的信号。最近的几篇文献报道表明， 不同皮质深度的fMRI反应幅度不同。然而，目前还没有确定是否 深度相关的fMRI实际上反映了不同皮质深度的局部神经网络的变化。以下是 目的试图验证功能磁共振成像具有差别层敏感性，与神经活动有意义地对应。 第一个目标是根据固有神经网络的已知属性来验证特定层功能磁共振成像。 而fMRI和电生理学测量由于行为或知觉引起的V1反应调制 过程(假定的反馈过程)不同意，但已经有充分的证据表明同意 FMRI和电生理测量内在神经反应(如对比敏感度)之间的差异 或定向选择性。因此，两组实验将量化依赖于深度的fMRI反应 简单的视觉刺激，对照电生理学预测的层流曲线，验证功能磁共振层流曲线。 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(图/背景)增强V1神经反应 均匀纹理(方向相关环绕)对V1神经反应的分割和抑制 抑制)在意识在调节V1中的调制中的作用方面有重要的不同。我们将量化 这两种不同语境调制下的fMRI层流图。因为这两个视觉特征 自闭症和自闭症等神经系统疾病会影响分组和等向抑制。 精神分裂症，验证了一种监测这些视觉背景调制机制的技术 在临床环境中的实用性。

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.