Neurophysiological distinctions between spatial and temporal context in episodic memory

Episodic memory refers to our ability to mentally retain personal experiences that occurred in a particular spatial and temporal context. Brain activity distinctions for spatial and temporal contexts have been observed via unicellular recordings and functional magnetic resonance imaging. However, these distinctions have not been examined using electrophysiological recordings of neural populations, such as event-related potentials (ERPs), because spatial and temporal contexts have been assessed separately. The aim was to examine electrophysiological activity distinctions between spatial and temporal contexts during encoding and retrieval. ERPs were recorded in 30 participants while they performed an associative task in which pairs of images were presented sequentially. During retrieval, participants identified whether the pair of images was spatially modified, temporally modified, identical, or new. The retrieval of spatial context was superior to that of temporal context. During the presentation of the second image of the pair, a frontal slow wave demonstrated subsequent memory effects for the correct temporal context. The FN400 was present during the recollection of the temporal context, and the parietal old/new effect was present during the recollection of the spatial context, both of which occurred when the first image of the pair was displayed. These patterns revealed that the temporal context (compared with the spatial context) required further encoding strategies and a strong distinction from familiarity at retrieval. Therefore, spatial and temporal contexts exhibit different brain activities during encoding and retrieval.