Electrophysiological signatures revealing the temporal dynamics of episodic retrieval

Episodic memory enables mental time travel, allowing us to relive specific, personally experienced events tied in time and place. This feat of human memory is considered to be dependent on the reinstatement of the cortical patterns that were active at the time of encoding. A growing body of recent literature has provided support for this idea by showing that retrieval success co-varies with the neural encoding patterns being reinstated at the time of retrieval. In this presentation, we will discuss findings from multivariate pattern analysis of electrophysiological data revealing the temporal dynamics of such reinstatement during retrieval and its consequences for episodic remembering. First, we will discuss both benefits and costs of cortical pattern reinstatement. Accumulating evidence has shown that memory typically benefits when the neural patterns established during encoding are reinstated during retrieval. However, our data show that reinstatement can also have detrimental effects on later episodic remembering depending on which aspects of the event are called-for. Next, we will show that contextual background features of an encoding episode are reinstated during selective retrieval even when such information is task-irrelevant. These data elucidate that context reinstatement tracks retrieval competition between similar episodes and interference resolution. Combined, our data elucidate the temporal dynamics of episodic remembering and shed new light on encoding and retrieval interactions in episodic memory

Benefits and costs of context reinstatement in episodic memory : An ERP study

This study investigated context-dependent episodic memory retrieval. An influential idea in the memory literature is that performance benefits when the retrieval context overlaps with the original encoding context. However, such memory facilitation may not be driven by the encoding-retrieval overlap per se but by the presence of diagnostic features in the reinstated context that discriminate the target episode from competing episodes. To test this prediction, the encoding-retrieval overlap and the diagnostic value of the context were manipulated in a novel associative recognition memory task. Participants were asked to memorize word pairs presented together with diagnostic (unique) and nondiagnostic (shared) background scenes. At test, participants recognized the word pairs in the presence and absence of the previously encoded contexts. Behavioral data show facilitated memory performance in the presence of the original context but, importantly, only when the context was diagnostic of the target episode. The electrophysiological data reveal an early anterior ERP encoding-retrieval overlap effect that tracks the cost associated with having nondiagnostic contexts present at retrieval, that is, shared by multiple previous episodes, and a later posterior encoding-retrieval overlap effect that reflects facilitated access to the target episode during retrieval in diagnostic contexts. Taken together, our results underscore the importance of the diagnostic value of the context and suggest that context-dependent episodic memory effects are multiple determined

Neural pattern classification tracks transfer-appropriate processing in episodic memory

The transfer-appropriate processing (TAP) account holds that episodic memory depends on the overlap between encoding and retrieval processing (e.g., perceptual or conceptual). In the current study, we employed multivariate pattern analysis (MVPA) of electroencephalography to examine the relevance of spontaneously engaged processing during encoding for later retrieval. Participants encoded word-picture associations, where the picture could be a famous face, a landmark, or an object. At test, we manipulated the retrieval demands by asking participants to retrieve either visual or verbal information about the pictures. MVPA revealed classification between picture categories during early perceptual stages of encoding (~170 ms). Importantly, these visual category-specific neural patterns were predictive of later episodic remembering, but the direction of the relationship was contingent on the particular retrieval demand of the memory task: a benefit for the visual and a cost for the verbal. A reinstatement of the category-specific neural patterns established during encoding was observed during retrieval, and again the relationship with behavior varied with retrieval demands. Reactivation of visual representations during retrieval was associated with better memory in the visual task, but lower memory performance in the verbal task. Taken together, our findings provide novel evidence in favor of the TAP account and further demonstrate that processing of particular aspects during memory formation can have detrimental effects on later episodic remembering when other aspects of the event are called-for

Mental reinstatement of encoding context improves episodic remembering

This study investigates context-dependent memory retrieval. Previous work has shown that physically re-experiencing the encoding context at retrieval improves memory accessibility. The current study examined if mental reconstruction of the original encoding context would yield parallel memory benefits. Participants performed a cued-recall memory task, preceded either by a mental or by a physical context reinstatement task, and we manipulated whether the context reinstated at retrieval overlapped with the context of the target episode. Both behavioral and electrophysiological measures of brain activity showed strong encoding-retrieval (E-R) overlap effects, with facilitated episodic retrieval when the encoding and retrieval contexts overlapped. The electrophysiological E-R overlap effect was more sustained and involved more posterior regions when context was mentally compared with physically reinstated. Additionally, a time-frequency analysis revealed that context reinstatement alone engenders recollection of the target episode. However, while recollection of the target memory is readily prompted by a physical reinstatement, target recollection during mental reinstatement is delayed and depends on the gradual reconstruction of the context. Taken together, our results show facilitated episodic remembering also when mentally reinstating the encoding context; and that such benefits are supported by both shared and partially non-overlapping neural mechanisms when the encoding context is mentally reconstructed as compared with physically presented at the time of retrieval

Neural pattern classification tracks transfer-appropriate processing in episodic memory

The transfer-appropriate processing (TAP) account holds that episodic memory depends on the overlap between encoding and retrieval processing. In the current study, we employed multivariate pattern analysis (MVPA) of electroencephalography to examine the relevance of spontaneously engaged visual processing during encoding for later retrieval. Human participants encoded word- picture associations, where the picture could be a famous face, a landmark, or an object. At test, we manipulated the retrieval demands by asking participants to retrieve either visual or verbal information about the pictures. MVPA revealed classification between picture categories during early perceptual stages of encoding (∼170 ms). Importantly, these visual category-specific neural patterns were predictive of later episodic remembering, but the direction of the relationship was contingent on the particular retrieval demand of the memory task: a benefit for the visual and a cost for the verbal. A reinstatement of the category-specific neural patterns established during encoding was observed during retrieval, and again the relationship with behavior varied with retrieval demands. Reactivation of visual representations during retrieval was associated with better memory in the visual task, but with lower performance in the verbal task. Our findings support and extend the TAP account by demonstrating that processing of particular aspects during memory formation can also have detrimental effects on later episodic remembering when other aspects of the event are called-for and shed new light on encoding and retrieval interactions in episodic memory

Neural correlates of mental context reinstatement supporting episodic memory retrieval

This study investigated if mental reinstatement of an encoding context during retrieval increases memory accessibility. Participants performed a cued-recall memory task where the overlap between encoding and retrieval context and the nature of context reinstatement (mental versus physical) were manipulated. Memory performance improved when the encoding-retrieval context overlapped in a comparable way for mental and physical context reinstatement. However, compared to physical reinstatement, mental reinstatement was characterized by later and more sustained ERP effects. Together, our results suggest that the access to episodic memories can be facilitated also by mentally reinstating the encoding context, and furthermore that such benefits may be supported by processes differently engaged than when the encoding context is physically re-presented at the time of retrieval

Remembering the past during new learning: the temporal dynamics of integrative encoding

Memories may integrate elements experienced in different events. For instance, meeting a woman leaving her house, and later meeting another woman entering the same house, may allow us to infer that the two women live together. Such memory representations are thought to rely on integrative encoding mechanisms, allowing us to make inferences about the world and generalize knowledge to entirely new situations. This study uses multivariate pattern analysis (MVPA) of electrophysiological data to elucidate the temporal dynamics of integrative encoding. We adapted the associative inference task to investigate cross- episode memory integration. Participants first learned overlapping paired associates, AB and CB pairs, that comprised a word and a picture (a face or a bird). Memory was later tested for the AC inferred associations, and for the direct AB and CB associations. MVPA was used to measure the online reactivation of previously learnt AB memories during encoding of the CB events. Reliable reactivation of AB was observed between 1.5 and 3 s. Participants (n=29) were divided into subgroups according to their AC performance: good and poor generalizers. Interestingly, while both groups showed comparable levels of AB reactivation during CB learning, the reactivation effects were associated with different consequences. For good generalizers, reactivation was predictive of later AC inference performance, suggesting that an integrated ABC representation was formed during BC learning. This interpretation is corroborated by behavioral data showing that direct and indirect inferred associations were retrieved equally fast. Altogether, this suggests that AC inference in this group of participants was based on integrative encoding mechanisms. Conversely, for poor generalizers, the reactivation of AB was instead negatively correlated with BC retrieval performance, indicating that AB reactivation impaired BC learning. Additionally, this group of participants took longer to retrieve inferred associations than direct associations, suggesting that successful AC inference was accomplished by flexibly recombining the direct AB and CB associations during retrieval. The present study extends previous literature by revealing the temporal dynamics of memory integration and providing an account of inter-individual differences in the capacity to make inferences across distinct episodes