Theta-Phase Targeted Encoding Gates Memory Sensitivity

Theta phase has been proposed to play an important role in memory. It may gate encoding and retrieval, such that certain phases are more favorable for memory processing than others, or become part of the memory representation, such that reinstating the encoding phase benefits retrieval. To test and distinguish these competing accounts, we used a closed-loop EEG system, allowing us to control the phase at which items were presented at encoding and retrieval. In an associative memory task, visual targets were presented at predefined phases of the ongoing mid-frontal theta rhythm, thereby pairing individual memory items with specific encoding phases. During retrieval, targets appeared either at the same phase as during encoding or at an alternative phase. We show that theta phase during encoding predicted subsequent memory sensitivity, while finding no evidence that retrieval phase nor the match between encoding and retrieval phases influenced performance. Therefore, our findings are consistent with a gating account, in which the rhythmic state at the moment of encoding influences the efficacy of memory formation.