Neural activity supporting the formation of associative memory versus source memory.

The ability to form a new association with discontiguous elements constitutes the very crux of episodic memory. However, it is not fully understood whether different types of associations rely on common neural correlates for encoding associations. In the present study, we investigated whether the formation of associative memory (associations between items) and source memory (associations between an item and its context) recruits common neural activity during encoding, or whether each type of association requires different neural activity for subsequent memory. During study, participants were visually presented a list of object pairs in the scanner while the names of objects were simultaneously presented either in a male or female voice. Participants completed a post-scan recognition test for associative and source memories for object pairs and their contexts. Associative memory was predicted in the left inferior prefrontal cortex, the fusiform gyrus and the medial temporal lobe including both perirhinal and parahippocampal cortices and the posterior hippocampus. Encoding activity for source memory was identified in the right insula and the right anterior hippocampus. Further, neural activity in the right posterior hippocampus was recruited for successful formation of both associative and source memories. Collectively, these findings highlight the pivotal role of the hippocampus in successful encoding of associative and source memories and add more weight to the role of the perirhinal cortex in associative encoding of objects. The present findings have implications for roles of the medial temporal lobe sub-regions for successful formation of associative and source memories.