Behavioural and Cognitive Neuroscience (Beacon) Seminar: How we remember and how we forget

Our ability to remember complex real-world events is thought to be supported by ‘event engrams’ – coherent representations of the constituent elements of any event that allow for later recollection. The hippocampus is thought to support these representations, receiving input from multiple neocortical regions to bind together the multiple elements of any event. At retrieval, a partial cue is thought to lead to the retrieval of a complete event engram (pattern completion) and subsequent reinstatement in the neocortex. I will present behavioural, computational and fMRI evidence to support the proposal that recollection is supported by the existence of complex event engrams in the hippocampus that are retrieved and reinstated by a pattern completion process. I will then ask how such event engrams are forgotten – do they fragment such that we forget some aspects of an event whilst retaining others, or are they forgotten in a relatively all-or-none fashion? Across a body of research, I will provide evidence that complex events are both remembered and forgotten in a relatively all-or-none manner – event engrams are encoded in a highly coherent manner and retain this coherence over time.