Misaki Masaya, Luh Wen-Ming, Bandettini Peter A
Section on Functional Imaging Methods, Laboratory of Brain and Cognition, National Institute of Mental Health, National Institutes of Health, 10 Center Dr. MSC 1148, Bethesda, MD 20892-1148 USA.
Functional MRI Facility, National Institute of Mental Health, National Institutes of Health. 10 Center Dr. MSC 1148, Bethesda, MD 20892-1148 USA.
Neuroimage. 2013 Feb 1;66:623-33. doi: 10.1016/j.neuroimage.2012.10.069. Epub 2012 Nov 2.
We investigated the decoding of ocular dominance stimulations with millisecond-order timing difference from the blood oxygen level dependent (BOLD) signal in human functional magnetic resonance imaging (fMRI). In our experiment, ocular dominance columns were activated by monocular visual stimulation with 500- or 100- ms onset differences. We observed that the event-related hemodynamic response (HDR) in the human visual cortex was sensitive to the subtle onset difference. The HDR shapes were related to the stimulus timings in various manners: the timing difference was represented in either the amplitude of positive peak, amplitude of negative peak, delay of peak time, or response duration of HDR. These complex relationships were different across voxels and subjects. To find an informative feature of HDR for discriminating the subtle timing difference of ocular dominance stimulations, we examined various characteristics of HDR including response amplitude, time to peak, full width at half-maximum response, as inputs for decoding analysis. Using a canonical HDR function for estimating the voxel's response did not yield good decoding scores, suggesting that information may reside in the variability of HDR shapes. Using all the values from the deconvolved HDR also showed low performance, which could be due to an over-fitting problem with the large data dimensionality. When using either positive or negative peak amplitude of the deconvolved HDR, high decoding performance could be achieved for both the 500ms and the 100ms onset differences. The high accuracy even for the 100ms difference, given that the signal was sampled at a TR of 250ms and 2×2×3-mm voxels, implies a possibility of spatiotemporally hyper-resolution decoding. Furthermore, both down-sampling and smoothing did not affect the decoding accuracies very much. These results suggest a complex spatiotemporal relationship between the multi-voxel pattern of the BOLD response and the population activation of neuronal columns. The demonstrated possibility of decoding stimulations for columnar-level organization with 100-ms onset difference using lower resolution imaging data may broaden the scope of application of the BOLD fMRI.
我们在人类功能磁共振成像（fMRI）中，研究了根据血氧水平依赖（BOLD）信号中毫秒级的时间差异来解码眼优势刺激。在我们的实验中，通过单眼视觉刺激激活眼优势柱，刺激起始差异为500毫秒或100毫秒。我们观察到人类视觉皮层中的事件相关血流动力学反应（HDR）对这种细微的起始差异很敏感。HDR的形状以多种方式与刺激时间相关：时间差异体现在正峰值幅度、负峰值幅度、峰值时间延迟或HDR的响应持续时间中。这些复杂的关系在体素和受试者之间各不相同。为了找到用于区分眼优势刺激细微时间差异的HDR信息特征，我们检查了HDR的各种特征，包括响应幅度、峰值时间、半高宽响应等，作为解码分析的输入。使用标准HDR函数来估计体素响应并不能得到良好的解码分数，这表明信息可能存在于HDR形状的变异性中。使用去卷积后的HDR的所有值也显示出低性能，这可能是由于大数据维度导致的过拟合问题。当使用去卷积后的HDR的正峰值或负峰值幅度时，对于500毫秒和100毫秒的起始差异都能实现高解码性能。即使对于100毫秒的差异也具有高精度，考虑到信号是以250毫秒的重复时间（TR）和2×2×3毫米的体素进行采样的，这意味着存在时空超分辨率解码的可能性。此外，下采样和平滑对解码精度的影响都不大。这些结果表明了BOLD反应的多体素模式与神经元柱群体激活之间复杂的时空关系。利用较低分辨率成像数据对具有100毫秒起始差异的柱状水平组织刺激进行解码的可能性，可能会拓宽BOLD fMRI的应用范围。
