Upadhyay Jaymin, Ducros Mathieu, Knaus Tracey A, Lindgren Kristen A, Silver Andrew, Tager-Flusberg Helen, Kim Dae-Shik
Center for Biomedical Imaging, Department of Anatomy and Neurobiology, Boston University School of Medicine, 715 Albany Street, Boston, MA 02118, USA.
Cereb Cortex. 2007 Oct;17(10):2420-32. doi: 10.1093/cercor/bhl150. Epub 2006 Dec 26.
Human primary auditory cortex (PAC) is functionally organized in a tonotopic manner. Past studies have used neuroimaging to characterize tonotopic organization in PAC and found similar organization as that described in mammals. In contrast to what is known about PAC in primates and nonprimates, in humans, the structural connectivity within PAC has not been defined. In this study, stroboscopic event-related functional magnetic resonance imaging (fMRI) was utilized to reveal mirror symmetric tonotopic organization consisting of a high-low-high frequency gradient in PAC. Furthermore, diffusion tensor tractography and probabilistic mapping was used to study projection patterns within tonotopic areas. Based on earlier physiological and histological work in nonhuman PAC, we hypothesized the existence of cross-field isofrequency (homotopic) and within-field non-isofrequency (heterotopic)-specific axonal projections in human PAC. The presence of both projections types was found in all subjects. Specifically, the number of diffusion tensor imaging (DTI) reconstructed fibers projecting between high- and low-frequency regions was greater than those fibers projecting between 2 high-frequency areas, the latter of which are located in distinct auditory fields. The fMRI and DTI results indicate that functional and structural properties within early stages of the auditory processing stream are preserved across multiple mammalian species at distinct evolutionary levels.
人类初级听觉皮层（PAC）在功能上呈音频拓扑方式组织。过去的研究利用神经成像来描述PAC中的音频拓扑组织，并发现其与哺乳动物中描述的组织相似。与灵长类动物和非灵长类动物中已知的PAC情况不同，在人类中，PAC内的结构连接尚未明确。在本研究中，利用频闪事件相关功能磁共振成像（fMRI）揭示了PAC中由高-低-高频率梯度组成的镜像对称音频拓扑组织。此外，使用扩散张量纤维束成像和概率图谱来研究音频拓扑区域内的投射模式。基于早期在非人类PAC中的生理学和组织学研究，我们假设人类PAC中存在跨场等频率（同位）和场内非等频率（异位）特异性轴突投射。在所有受试者中均发现了这两种投射类型。具体而言，在高频和低频区域之间投射的扩散张量成像（DTI）重建纤维数量多于在两个高频区域之间投射的纤维数量，后者位于不同的听觉场中。fMRI和DTI结果表明，在不同进化水平的多个哺乳动物物种中，听觉处理流早期阶段的功能和结构特性得以保留。
