What precisely constitutes a “difference” in brain activity? The answer has implications for cognitive neuroscientists who use neuroimaging to test theories about whether different brain regions support different cognitive functions. In a recent paper in the Proceedings of the National Academy of Sciences, USA, Bernhard Staresina and colleagues introduce a new method called “state-trace analysis”, and show how it can be used to infer that different regions within the medial temporal lobe support different types of memory. This work was enabled by rare human intracranial data from collaborators in Bonn, Germany, and by methodological advice from collaborators in Adelaide, Australia. The senior author, Rik Henson, commented “This question has bugged me for years, so I am excited that we finally have a new tool in our scientific armoury to address it”.