SPM_3: Statistical parametric maps in functional imaging: A general linear approach Friston KJ, Holmes AP, Worsley KJ, Poline J-B, Frith CD & Frackowiak RSJ (1995) Human Brain Mapping 2:189-210 Abstract Statistical parametric maps are spatially extended statistical processes that are used to test hypotheses about regionally specific effects in neuroimaging data. The most established sorts of statistical parametric maps (e.g. Friston et al 1991, Worsley et al 1992) are based on linear models, for example ANCOVA, correlation coefficients and t tests. In the sense that these examples are all special cases of the general linear model it should be possible to implement them (and many others) within a unified framework. We present here a general approach that accommodates most forms of experimental layout and ensuing analysis (designed experiments with fixed effects for factors, covariates and interaction of factors). This approach brings together two well established bodies of theory (the general linear model and the theory of Gaussian Fields) to provide a complete and simple framework for the analysis of imaging data. The importance of this framework is twofold: (i) Conceptual and mathematical simplicity, in that the small number of operational equations used are the same, irrespective of the complexity of the experiment or nature of the statistical model and (ii) the generality of the framework provides for great latitude in experimental design and analysis. This is a general introduction to the general linear model in the context of functional imaging. Statistical parametric mapping can be seen as the combined use of the general liner model to create a spatially extended statistical process, that is then interpreted with reference to the theory of Gaussian fields.