Pattern completion for episodic events in the human hippocampus

The multiple elements of episodic events, represented in distinct neocortical regions, are thought to be bound into coherent ‘event engrams ’ by the hippocampus (Damasio, 1989; Tulving, 1983). These engrams should allow for the retrieval of all event elements via pattern completion, resulting in their ‘reinstatement ’ in the neocortex (Marr, 1971). We have previously shown behavioural dependency between retrieval of different elements of the same event (Horner & Burgess, 2013). For example, for location-person-object events, if we remember the location of a specific event we should be more likely to remember the person and object from that same event. We have further shown that this behavioural dependency is due to pattern completion at retrieval, rather than fluctuations in encoding strength (Horner & Burgess, 2014). Here we ask whether pattern completion is related to hippocampal activity and whether it results in the reinstatement of event elements in the neocortex. In an fMRI experiment, participants learned events consisting of distinct elements (locations, people and objects/animals). At retrieval, each pairwise association of each event was tested. At encoding, hippocampal activity predicts subsequent memory performance for all within-event elements, supporting the idea that the hippocampus bind