DiNuzzo Mauro, Mascali Daniele, Moraschi Marta, Bussu Giorgia, Maraviglia Bruno, Mangia Silvia, Giove Federico
Division of Glial Disease and Therapeutics, Faculty of Health and Medical Sciences, Center for Basic and Translational Neuroscience, University of Copenhagen, Copenhagen, Denmark.
Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi, Rome, Italy.
Front Phys. 2017;5. doi: 10.3389/fphy.2017.00007. Epub 2017 Feb 23.
Time-domain analysis of blood-oxygenation level-dependent (BOLD) signals allows the identification of clusters of voxels responding to photic stimulation in primary visual cortex (V1). However, the characterization of information encoding into temporal properties of the BOLD signals of an activated cluster is poorly investigated. Here, we used Shannon entropy to determine spatial and temporal information encoding in the BOLD signal within the most strongly activated area of the human visual cortex during a hemifield photic stimulation. We determined the distribution profile of BOLD signals during epochs at rest and under stimulation within small (19-121 voxels) clusters designed to include only voxels driven by the stimulus as highly and uniformly as possible. We found consistent and significant increases (2-4% on average) in temporal information entropy during activation in contralateral but not ipsilateral V1, which was mirrored by an expected loss of spatial information entropy. These opposite changes coexisted with increases in both spatial and temporal mutual information (i.e., dependence) in contralateral V1. Thus, we showed that the first cortical stage of visual processing is characterized by a specific spatiotemporal rearrangement of intracluster BOLD responses. Our results indicate that while in the space domain BOLD maps may be incapable of capturing the functional specialization of small neuronal populations due to relatively low spatial resolution, some information encoding may still be revealed in the temporal domain by an increase of temporal information entropy.
血氧水平依赖（BOLD）信号的时域分析能够识别初级视觉皮层（V1）中对光刺激产生反应的体素簇。然而，对于激活簇的BOLD信号的时间特性中信息编码的特征研究较少。在此，我们使用香农熵来确定在半视野光刺激期间人类视觉皮层最强激活区域内BOLD信号的空间和时间信息编码。我们确定了在静止期和刺激期内，在小（19 - 121个体素）簇中的BOLD信号分布情况，这些簇被设计为尽可能高度且均匀地仅包含由刺激驱动的体素。我们发现在对侧V1激活期间，时间信息熵持续且显著增加（平均增加2 - 4%），而同侧V1则没有，这与空间信息熵的预期损失相对应。这些相反的变化与对侧V1中空间和时间互信息（即依赖性）的增加同时存在。因此，我们表明视觉处理的第一皮层阶段的特征是簇内BOLD反应的特定时空重排。我们的结果表明，虽然在空间域中，由于相对较低的空间分辨率，BOLD图谱可能无法捕捉小神经元群体的功能特化，但时间信息熵的增加仍可能在时间域中揭示一些信息编码。
