Spatiotemporal dynamics of memory encoding and memory retrieval states

Abstract Memory encoding and memory retrieval are neurally distinct brain states that can be differentiated on the basis of cortical network activity. However, it is unclear whether sustained engagement of one network or fluctuations between multiple networks give rise to these memory states. The spatiotemporal dynamics of memory states may have important implications for memory behavior and cognition; however, measuring temporally resolved signals of cortical networks poses a challenge. Here we recorded scalp electroencephalography from subjects performing a mnemonic state task in which they were biased toward memory encoding or retrieval. We performed a microstate analysis in order to measure the temporal dynamics of cortical networks throughout this mnemonic state task. We find that microstate E, a putative analog of the default mode network, shows temporally sustained dissociations between memory encoding and retrieval, with greater engagement during retrieve compared to encode trials. We further show that decreased engagement of microstate E is a general property of encoding, rather than a reflection of retrieval suppression. Together, these findings show that memory states are supported by sustained engagement of a particular cortical network. Memory success, as well as cognition more broadly, may be influenced by the ability to engage or disengage microstate E in a goal-dependent manner.