Abstract
Systems-level consolidation is the time-dependent reorganisation of a memory trace in the neocortex, with the ventromedial prefrontal cortex (vmPFC) being particularly implicated. Capturing the precise temporal evolution of this crucial process in humans has long proved elusive. Here, we used multivariate methods and a longitudinal functional MRI design to detect, with high granularity, the extent to which autobiographical memories of different ages were represented in vmPFC and how this changed over time. We observed an unexpected biphasic involvement of vmPFC during retrieval, rising and falling around an initial peak of 8-12 months, before re-engaging for older two and five year old memories. Remarkably, when re-examined eight months later, representations of individual memories had undergone their hypothesised strengthening or weakening over time. We conclude that the temporal recruitment of vmPFC in autobiographical memory retrieval seems to be non-linear, revealing a previously-unknown feature of systems-level consolidation that is absent from current theories.