Multivariate decoding and brain reading: introduction to the special issue.

In recent years, the scope of neuroimaging research has been substantially extended by multivariate decoding methodology. Decoding techniques allow us to address a number of important questions that are frequently neglected in more conventional analyses. They allow us to focus on storage of "mental content" in brain regions, rather than on overall levels of activation. They directly address the question how much information can be "read out" of brain activity patterns, thus inverting the classical direction of inference that attempts to explain brain activity from mental state variables. At the same time, they provide a much higher sensitivity to detection of effects than conventional approaches. This special issue is a showcase of research in this emerging field. Besides five invited review papers by key experts in the field, it presents a representative selection of work showing the diversity and power of multivariate decoding analyses ranging from methodological foundations to cognitive and clinical studies.