Seghier Mohamed L, Lazeyras François, Pegna Alan J, Annoni Jean-Marie, Khateb Asaid
Department of Radiology, Geneva University Hospitals, Geneva, Switzerland.
Hum Brain Mapp. 2008 Apr;29(4):461-77. doi: 10.1002/hbm.20410.
Before considering a given fMRI paradigm as a valid clinical tool, one should first assess the reliability of functional responses across subjects by establishing a normative database and defining a reference activation map that identifies major brain regions involved in the task at hand. However, the definition of such a reference map can be hindered by inter-individual functional variability. In this study, we analysed functional data obtained from 50 healthy subjects during a semantic language task to assess the influence of the number of subjects on the reference map and to characterise inter-individual functional variability. We first compared different group analysis approaches and showed that the extent of the activated network depends not only on the choice of the analysis approach but also on the statistical threshold used and the number of subjects included. This analysis suggested that, while the RFX analysis is suitable to detect confidently true positive activations, the other group approaches are useful for exploratory investigations in small samples. The application of quantitative measures at the voxel and regional levels suggested that while approximately 15-20 subjects were sufficient to reveal reliable and robust left hemisphere activations, >30 subjects were necessary for revealing more variable and weak right hemisphere ones. Finally, to visualise inter-individual variability, we combined two similarity indices that assess the percentages of true positive and false negative voxels in individual activation patterns relative to the group map. We suggest that these measures can be used for the estimation of the degree of 'normality' of functional responses in brain-damaged patients, where this question is often raised, and recommend the use of different quantifications to appreciate accurately the inter-individual functional variability that can be incorporated in group maps.
在将特定的功能磁共振成像（fMRI）范式视为有效的临床工具之前，首先应通过建立一个标准数据库并定义一个参考激活图谱来评估不同受试者之间功能反应的可靠性，该图谱可识别参与手头任务的主要脑区。然而，个体间功能变异性可能会阻碍这种参考图谱的定义。在本研究中，我们分析了50名健康受试者在语义语言任务期间获得的功能数据，以评估受试者数量对参考图谱的影响，并描述个体间功能变异性。我们首先比较了不同的组分析方法，结果表明激活网络的范围不仅取决于分析方法的选择，还取决于所使用的统计阈值和纳入的受试者数量。该分析表明，虽然随机效应分析（RFX）适用于可靠地检测真正的阳性激活，但其他组分析方法对于小样本的探索性研究很有用。在体素和区域水平应用定量测量表明，虽然大约15 - 20名受试者足以揭示可靠且稳健的左半球激活，但要揭示更多变异性和较弱的右半球激活则需要超过30名受试者。最后，为了可视化个体间的变异性，我们结合了两个相似性指数，这两个指数评估个体激活模式中相对于组图谱的真阳性和假阴性体素的百分比。我们建议这些测量方法可用于估计脑损伤患者功能反应的“正常”程度，在这种情况下这个问题经常被提出，并建议使用不同的量化方法来准确评估可纳入组图谱的个体间功能变异性。
