Henriksson Linda, Khaligh-Razavi Seyed-Mahdi, Kay Kendrick, Kriegeskorte Nikolaus
MRC Cognition and Brain Sciences Unit, Cambridge CB2 7EF, UK; Brain Research Unit, Department of Neuroscience and Biomedical Engineering, Aalto University, 02150 Espoo, Finland.
MRC Cognition and Brain Sciences Unit, Cambridge CB2 7EF, UK; Computer Science & Artificial Intelligence Laboratory, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Neuroimage. 2015 Jul 1;114:275-86. doi: 10.1016/j.neuroimage.2015.04.026. Epub 2015 Apr 17.
Intrinsic cortical dynamics are thought to underlie trial-to-trial variability of visually evoked responses in animal models. Understanding their function in the context of sensory processing and representation is a major current challenge. Here we report that intrinsic cortical dynamics strongly affect the representational geometry of a brain region, as reflected in response-pattern dissimilarities, and exaggerate the similarity of representations between brain regions. We characterized the representations in several human visual areas by representational dissimilarity matrices (RDMs) constructed from fMRI response-patterns for natural image stimuli. The RDMs of different visual areas were highly similar when the response-patterns were estimated on the basis of the same trials (sharing intrinsic cortical dynamics), and quite distinct when patterns were estimated on the basis of separate trials (sharing only the stimulus-driven component). We show that the greater similarity of the representational geometries can be explained by coherent fluctuations of regional-mean activation within visual cortex, reflecting intrinsic dynamics. Using separate trials to study stimulus-driven representations revealed clearer distinctions between the representational geometries: a Gabor wavelet pyramid model explained representational geometry in visual areas V1-3 and a categorical animate-inanimate model in the object-responsive lateral occipital cortex.
在动物模型中，内在皮质动力学被认为是视觉诱发反应逐次试验变异性的基础。在感觉处理和表征的背景下理解它们的功能是当前的一项重大挑战。在此我们报告，内在皮质动力学强烈影响一个脑区的表征几何结构，这在反应模式差异中得以体现，并夸大了不同脑区之间表征的相似性。我们通过基于功能磁共振成像（fMRI）对自然图像刺激的反应模式构建的表征差异矩阵（RDM）来刻画人类多个视觉区域的表征。当基于相同试验（共享内在皮质动力学）估计反应模式时，不同视觉区域的RDM高度相似；而当基于单独试验（仅共享刺激驱动成分）估计模式时，则截然不同。我们表明，表征几何结构更大的相似性可由视觉皮质内区域平均激活的相干波动来解释，这反映了内在动力学。使用单独试验来研究刺激驱动的表征揭示了表征几何结构之间更清晰的差异：一个Gabor小波金字塔模型解释了V1 - 3视觉区域的表征几何结构，以及一个关于物体反应性外侧枕叶皮质中分类有生命 - 无生命物体的模型。
