Brain representations of space and time in episodic memory: A systematic review and meta-analysis.

All experiences preserved within episodic memory contain information on the space and time of events. The hippocampus is the main brain region involved in processing spatial and temporal information for incorporation within episodic memory representations. However, the other brain regions involved in the encoding and retrieval of spatial and temporal information within episodic memory are unclear, because a systematic review of related studies is lacking and the findings are scattered. The present study was designed to integrate the results of functional magnetic resonance imaging and positron emission tomography studies by means of a systematic review and meta-analysis to provide converging evidence. In particular, we focused on identifying the brain regions involved in the retrieval of spatial and temporal information. We identified a spatial retrieval network consisting of the inferior temporal gyrus, parahippocampal gyrus, superior parietal lobule, angular gyrus, and precuneus. Temporal context retrieval was supported by the dorsolateral prefrontal cortex. Thus, the retrieval of spatial and temporal information is supported by different brain regions, highlighting their different natures within episodic memory.

Retrieving effectively from source memory: Evidence for differentiation and local matching processes.

The ability to distinguish between different explanations of human memory abilities continues to be the subject of many ongoing theoretical debates. These debates attempt to account for a growing corpus of empirical phenomena in item-memory judgments, which include the list strength effect, the strength-based mirror effect, and output interference. One of the main theoretical contenders is the Retrieving Effectively from Memory (REM) model. We show that REM, in its current form, has difficulties in accounting for source-memory judgments - a situation that calls for its revision. We propose an extended REM model that assumes a local-matching process for source judgments alongside source differentiation. We report a first evaluation of this model's predictions using three experiments in which we manipulated the relative source-memory strength of different lists of items. Analogous to item-memory judgments, we observed a null list strength effect and a strength-based mirror effect in the case of source memory. In a second evaluation, which relied on a novel experiment alongside two previously published datasets, we evaluated the model's predictions regarding the manifestation of output interference in item and lack of it in source memory judgments. Our results showed output interference severely affecting the accuracy of item-memory judgments but having a null or negligible impact when it comes to source-memory judgments. Altogether, these results support REM's core notion of differentiation (for both item and source information) as well as the concept of local matching proposed by the present extension.

The ownership memory self-reference effect shifts recognition criterion but not recognition sensitivity.

Information referenced to the self is retrieved more accurately than information referenced to others, known as the memory self-reference effect. It is unclear, however, whether social context (identity of the other) or task factors alter decision-making processes. In a virtual object allocation task, female participants sorted objects into their own or another's (stranger or mother) basket based on a colour cue. Subsequently, they performed a recognition memory task in which they first indicated whether each object was old or new, and then whether it had been allocated to themselves or to the other. We obtained owner-specific hit rates and false-alarm rates and applied signal detection theory to derive separate recognition sensitivity (d') and recognition criterion parameters (c) for self- and other-owned objects. While there was no clear evidence of a recognition self-reference effect, or a change in sensitivity, participants adopted a more conservative recognition criterion for self- compared with other-owned objects, and particularly when the other-referent was the participant's mother compared with the stranger. Moreover, when discriminating whether the originally presented objects were self- or other-owned, participants were biased toward ascribing ownership to the 'other'. We speculate that these findings reflect ownership-based changes in decisional processing during the recognition memory self-reference paradigm.

Multisensory processing impacts memory for objects and their sources.

Multisensory object processing improves recognition memory for individual objects, but its impact on memory for neighboring visual objects and scene context remains largely unknown. It is therefore unclear how multisensory processing impacts episodic memory for information outside of the object itself. We conducted three experiments to test the prediction that the presence of audiovisual objects at encoding would improve memory for nearby visual objects, and improve memory for the environmental context in which they occurred. In Experiments 1a and 1b, participants viewed audiovisual-visual object pairs or visual-visual object pairs with a control sound during encoding and were subsequently tested on their memory for each object individually. In Experiment 2, objects were paired with semantically congruent or meaningless control sounds and appeared within four different scene environments. Memory for the environment was tested. Results from Experiments 1a and 1b showed that encoding a congruent audiovisual object did not significantly benefit memory for neighboring visual objects, but Experiment 2 showed that encoding a congruent audiovisual object did improve memory for the environments in which those objects were encoded. These findings suggest that multisensory processing can influence memory beyond the objects themselves and that it has a unique role in episodic memory formation. This is particularly important for understanding how memories and associations are formed in real-world situations, in which objects and their surroundings are often multimodal.

Who said what to whom? Memory for sources and destinations in monolinguals and bilinguals.

Two experiments with monolingual and bilingual participants tested memory for sources (speakers) and destinations (listeners) in conversations consisting of self-referential statements. In Experiment 1, participants directly interacted in English conversations with audio-visually recorded confederates. In Experiment 2, participants observed recorded conversations among confederates. In both conversational situations, source memory was more accurate than destination memory, indicating that the attentional resources consumed by self-focus or sentence production/completion do not explain why destinations are less well remembered than sources in direct-interaction conversations. Source and destination memory were positively associated with item memory at the participant level, indicating that stronger item encoding is associated with stronger encoding of contextual information. In the observed conversations, source and destination accuracy were negatively associated at the trial level, indicating that these features of the memory episode are not encoded independently, and there is a tradeoff in the encoding of these contextual features. Item memory did not differ for monolinguals and bilinguals and was positively associated with proficiency only in conversations with direct interaction. In the observational setting (but not the direct-interaction setting), source and destination memory were more accurate for bilinguals than monolinguals. This finding suggests that bilinguals allocate attention more efficiently than monolinguals when the cognitive demands of sentence production are eliminated. Proficiency in English was positively associated with memory for the appropriate conversational partner only when participants had to produce sentence frames and complete them with self-generated information, suggesting that language proficiency is beneficial when cognitive demands are high.

The limited memory of value following value directed encoding.

Items associated with higher values during encoding are later recognized and recalled better than are lower valued items. During recall paradigms, these value directed encoding (VDE) effects heavily depend upon learned strategies acquired during repeated testing with earnings feedback. However, because VDE effects also occur in single test recognition designs, precluding such learning, it has been suggested that high value may automatically induce good encoding. We tested this by manipulating encoding instructions (Experiments 1a and 1b) and manipulating concurrent levels of processing (LOP) requirements during encoding (Experiment 2a and 2b). Two main findings emerged. First, subject initiated strategies played a dominant role in VDE effects with little evidence for automaticity. This was demonstrated in Experiment 1 by a more than three-fold increase in the VDE recognition effect when instructions specifically encouraged selective elaboration of high-value items. It was also shown by the complete elimination of VDE recognition effects in Experiment 2 when LOP tasks were concurrently performed during encoding. Critically, the blocking of VDE effects occurred even though a catch trial procedure verified that value was being processed during encoding and remained even when subjects had unlimited time to process the materials during encoding. Second, the data showed, for the first time, that when subjects attempted to specify the value of recognized items, they heavily depended upon a recognition heuristic in which increases in recognition strength, even when nondiagnostic, were inferred to reflect high encoding value. The tendency for subjects to conflate recognition strength and value may have important implications for behavioral economics.

Does sleep benefit source memory? Investigating 12-h retention intervals with a multinomial modeling approach.

For retention intervals of up to 12 h, the active systems consolidation hypothesis predicts that sleep compared to wakefulness strengthens the context binding of memories previously established during encoding. Sleep should thus improve source memory. By comparing retention intervals filled with natural night sleep versus daytime wakefulness, we tested this prediction in two online source-monitoring experiments using intentionally learned pictures as items and incidentally learned screen positions and frame colors as source dimensions. In Experiment 1, we examined source memory by varying the spatial position of pictures on the computer screen. Multinomial modeling analyses revealed a significant sleep benefit in source memory. In Experiment 2, we manipulated both the spatial position and the frame color of pictures orthogonally to investigate source memory for two different source dimensions at the same time, also allowing exploration of bound memory for both source dimensions. The sleep benefit on spatial source memory replicated. In contrast, no source memory sleep benefit was observed for either frame color or bound memory of both source dimensions, probably as a consequence of a floor effect in incidental encoding of color associations. In sum, the results of both experiments show that sleep within a 12-h retention interval improves source memory for spatial positions, supporting the prediction of the active systems consolidation hypothesis. However, additional research is required to clarify the impact of sleep on source memory for other context features and bound memories of multiple source dimensions.

The effects of forewarning and divided attention on context retrieval in false recognition.

After studying a list of words that are semantically associated to a critical lure, participants are more likely to attribute a falsely recognised critical lure to the context of its strong than weak semantic associates. This is known as the source-strength effect. The current study investigated the roles of automatic and controlled processing in context retrieval in false recognition that is demonstrated by the source-strength effect. The results revealed that the source-strength effect was impervious to forewarning (Experiment 1) and remained intact when attentional resources at encoding were reduced (Experiment 2), suggesting that context retrieval in false recognition is based on automatic processes that are not amenable to conscious control and do not require many attentional resources. This interpretation is consistent with the associative activation theory, which proposes that context retrieval in false recognition is based on memory associations between contexts and critical lures that are automatically created when critical lures become automatically activated via spreading activation process.

Enhanced source memory for emotionally valenced sources: does an affective orienting task make the difference?

Previous research on whether source memory is enhanced for emotionally valenced sources yielded inconclusive results. To identify potential boundary conditions, we tested whether encoding instructions that promote affective versus different types of non-affective item-source-processing foster versus hamper source-valence effects. In both experiments, we used neutral words as items superimposed on emotional (positive & negative) or neutral pictures as sources. Source pictures were selected based on valence and arousal ratings collected in a pre-study such that only valence varied across sources. Source memory was measured via multinomial modelling. In Experiment 1, we applied an affective, item-focused orienting task (OT; i.e. word-pleasantness ratings) during item-source encoding and found enhanced source memory for emotionally valenced (positive & negative) compared to neutral sources. In Experiment 2, we systematically manipulated encoding instructions and again found enhanced source memory for emotionally valenced sources with an affective OT. No such effects occurred in the non-affective conditions, where participants were instructed to integrate item and source (item-source-fit judgments), to focus on the item (living-non-living judgments), or to encode the items only, respectively. With intentional item encoding, however, source memory was surprisingly better for positive than negative sources. We conclude that source-valence effects might unfold only under affective processing.

Midbrain-Hippocampus Structural Connectivity Selectively Predicts Motivated Memory Encoding.

Motivation is a powerful driver of learning and memory. Functional MRI studies show that interactions among the dopaminergic midbrain substantia nigra/ventral tegmental area (SN/VTA), hippocampus, and nucleus accumbens (NAc) are critical for motivated memory encoding. However, it is not known whether these effects are transient and purely functional, or whether individual differences in the structure of this circuit underlie motivated memory encoding. To quantify individual differences in structure, diffusion-weighted MRI and probabilistic tractography were used to quantify SN/VTA-striatum and SN/VTA-hippocampus pathways associated with motivated memory encoding in humans. Male and female participants completed a motivated source memory paradigm. During encoding, words were randomly assigned to one of three conditions, reward ($1.00), control ($0.00), or punishment (-$1.00). During retrieval, participants were asked to retrieve item and source information of the previously studied words and were rewarded or penalized according to their performance. Source memory for words assigned to both reward and punishment conditions was greater than those for control words, but there were no differences in item memory based on value. Anatomically, probabilistic tractography results revealed a heterogeneous, topological arrangement of the SN/VTA. Tract density measures of SN/VTA-hippocampus pathways were positively correlated with individual differences in reward-and-punishment-modulated memory performance, whereas density of SN/VTA-striatum pathways showed no association. This novel finding suggests that pathways emerging from the human SV/VTA are anatomically separable and functionally heterogeneous. Individual differences in structural connectivity of the dopaminergic hippocampus-VTA loop are selectively associated with motivated memory encoding.SIGNIFICANCE STATEMENT Functional MRI studies show that interactions among the SN/VTA, hippocampus, and NAc are critical for motivated memory encoding. This has led to competing theories that posit either SN/VTA-NAc reward prediction errors or SN/VTA-hippocampus signals underlie motivated memory encoding. Additionally, it is not known whether these effects are transient and purely functional or whether individual differences in the structure of these circuits underlie motivated memory encoding. Using diffusion-weighted MRI and probabilistic tractography, we show that tract density measures of SN/VTA-hippocampus pathways are positively correlated with motivated memory performance, whereas density of SN/VTA-striatum pathways show no association. This finding suggests that anatomic individual differences of the dopaminergic hippocampus-VTA loop are selectively associated with motivated memory encoding.

Sensitivity of late ERP old/new effects in source memory to self-referential encoding focus and stimulus emotionality.

In episodic memory, the old/new effect, the contrast of the waveforms elicited by the correctly recognized studied items and the correctly rejected novel items, has been broadly concerned. However, the contribution of self-referential encoding to the old/new effect in source memory (i.e., source-SRE), is far from clarification; further, it remains unclear whether the contribution is susceptible to the factor of stimulus emotionality. To address these issues, adopting the event-related potential (ERP) technique, this study applied words of three types of emotional valences (positive, neutral, vs. negative) in the self-focus vs. external-focus encoding tasks. In the course of the test, four ERP old/new effects were identified: (a) the familiarity- and recollection-reflected mid-frontal effect (FN400) and late positive component (LPC) were both independent of source-SRE and stimulus emotionality; (b) the reconstruction-driven late posterior negativity (LPN) exhibited an adverse pattern of source-SRE and was susceptible to the emotional valence by encoding focus; and (c) the right frontal old/new effect (RFE), reflecting post-retrieval process, exhibited a source-SRE in emotional words. These effects provide compelling evidence for the influences of both stimulus valence and encoding focus on SRE in source memory, especially during the late processes. Further directions considering more perspectives are put forward.

The spatiotemporal gradient of intrusion errors in continuous outcome source memory: Source retrieval is affected by both guessing and intrusions.

Previous research has characterized source retrieval as a thresholded process, which fails on a proportion of trials and leads to guessing, as opposed to a continuous process, in which response precision varies across trials but is never zero. The thresholded view of source retrieval is largely based on the observation of heavy tailed distributions of response errors, thought to reflect a large proportion of "memoryless" trials. In this study, we investigate whether these errors might instead reflect systematic intrusions from other list items which can mimic source guessing. Using the circular diffusion model of decision making, which accounts for both response errors and RTs we found that intrusions account for some, but not all, errors in a continuous-report source memory task. We found that intrusion errors were more likely to come from items studied in nearby locations and times, and were well-described by a spatiotemporal gradient model, but not from semantically or perceptually similar cues. Our findings support a thresholded view of source retrieval but suggest that previous work has overestimated the proportion of guesses which have been conflated with intrusions.

Impaired cognitive performance in older adults is associated with deficits in item memory and memory for object features.

Amnestic mild cognitive impairment (aMCI) is associated with damage to the perirhinal/entorhinal cortex, and consequently, deficits in item/object memory. However, cognitive assessments commonly used to identify individuals with aMCI require a clinician to administer and interpret the test. We developed a novel self-administered global cognitive assessment, called the Cognitive Assessment via Keyboard (CAKe). To assess the relationship between CAKe performance and perirhinal/entorhinal cortex-dependent memory function, participants completed the CAKe, a feature source memory task, and a context memory task. During the memory tasks, participants studied line drawings with either a green or orange internal color (feature memory runs) or external color (context memory runs) and then classified each item as old and previously presented with a "green" or "orange" color, or "new". CAKe scores were correlated with item memory accuracies and source memory accuracies on both tasks. Participants with 'impaired' CAKe performance had worse item memory and worse feature source memory accuracies than those with 'normal' CAKe performance. These results demonstrate specific deficits in item memory and feature source memory and suggest that our assessments may be a valid predictor of aMCI memory deficits.

The effects of variable encoding contexts on item and source recognition.

How repeated encoding affects retention of item details is an unresolved question. The Competitive Trace theory (Yassa & Reagh, Frontiers in Behavioral Neuroscience, 7, 107, 2013) assumes that even slight variations in encoding contexts across item repetitions induce competition among non-overlapping contextual traces, leading to semanticization and decontextualized memory traces. However, empirical support for this assumption is mixed. In extension of previous research, the current study attempted to increase the competition between contextual traces by increasing encoding context variability. In three experiments we tested how repeated encoding in the same context or different contexts affects target recognition, similar lure discrimination, and source memory. Participants viewed images of objects once, three times in the same or three times in different contexts. Context variability was implemented through variations in background color or encoding tasks. Repeated encoding improved memory for item details, independent of context variability. Background color was poorly remembered but answering different encoding questions for repeated items impaired recollection of specific encoding tasks, in comparison to encoding items only once or repeatedly with the same encoding task. Our findings show that repetitions enhance memory for perceptual details but can impair memory for contextual elements, a dissociation that needs to be considered by the Competitive Trace Theory and other consolidation theories.

Emotional dissociations in temporal associations: opposing effects of arousal on memory for details surrounding unpleasant events.

Research targeting emotion's impact on relational episodic memory has largely focused on spatial aspects, but less is known about emotion's impact on memory for an event's temporal associations. The present research investigated this topic. Participants viewed a series of interspersed negative and neutral images with instructions to create stories linking successive images. Later, participants performed a surprise memory test, which measured temporal associations between pairs of consecutive pictures where one picture was negative and one was neutral. Analyses focused on how the order of negative and neutral images during encoding influenced retrieval accuracy. Converging results from a discovery study (N = 72) and pre-registered replication study (N = 150) revealed a "forward-favouring" effect of emotion in temporal memory encoding: Participants encoded associations between negative stimuli and subsequent neutral stimuli more strongly than associations between negative stimuli and preceding neutral stimuli. This finding may reflect a novel trade-off regarding emotion's effects on memory and is relevant for understanding affective disorders, as key clinical symptoms can be conceptualised as maladaptive memory retrieval of temporal details.

How Behavior Shapes the Brain and the Brain Shapes Behavior: Insights from Memory Development.

Source memory improves substantially during childhood. This improvement is thought to be closely related to hippocampal maturation. As previous studies have mainly used cross-sectional designs to assess relations between source memory and hippocampal function, it remains unknown whether changes in the brain precede improvements in memory or vice versa. To address this gap, the current study used an accelerated longitudinal design (n = 200, 100 males) to follow 4- and 6-year-old human children for 3 years. We traced developmental changes in source memory and intrinsic hippocampal functional connectivity and assessed differences between the 4- and 6-year-old cohorts in the predictive relations between source memory changes and intrinsic hippocampal functional connectivity in the absence of a demanding task. Consistent with previous studies, there were age-related increases in source memory and intrinsic functional connectivity between the hippocampus and cortical regions known to be involved during memory encoding. Novel findings showed that changes in memory ability early in life predicted later connectivity between the hippocampus and cortical regions and that intrinsic hippocampal functional connectivity predicted later changes in source memory. These findings suggest that behavioral experience and brain development are interactive, bidirectional processes, such that experience shapes future changes in the brain and the brain shapes future changes in behavior. Results also suggest that both timing and location matter, as the observed effects depended on both children's age and the specific brain ROIs. Together, these findings add critical insight into the interactive relations between cognitive processes and their underlying neurologic bases during development.SIGNIFICANCE STATEMENT Cross-sectional studies have shown that the ability to remember the contextual details of previous experiences (i.e., source memory) is related to hippocampal development in childhood. It is unknown whether hippocampal functional changes precede improvements in memory or vice versa. By using an accelerated longitudinal design, we found that early source memory changes predicted later intrinsic hippocampal functional connectivity and that this connectivity predicted later source memory changes. These findings suggest that behavioral experience and brain development are interactive, bidirectional processes, such that experience shapes future changes in the brain and the brain shapes future behavioral changes. Moreover, these interactions varied as a function of children's age and brain region, highlighting the importance of a developmental perspective when investigating brain-behavior interactions.

Interactions between the hippocampus and fronto-parietal regions during memory encoding in early childhood.

The neural mechanisms underlying memory encoding have received much attention in the literature. Research in adults and school-age children suggest that the hippocampus and cortical regions in both frontal and parietal areas are involved in successful formation of memories. Overall, the hippocampus has been shown to interact with fronto-parietal regions to collaboratively support successful memory encoding for both individual items as well as item details (such as the source or color in which the item was originally encountered). To date, only one study has investigated neural regions engaged during memory encoding in children younger than 8 years of age, which is unfortunate since early childhood is a period of dramatic improvement in memory. This previous study indicated that both the hippocampus and cortical regions are involved during the encoding of subsequently remembered item details (i.e., sources). However, this study reported few interactions between these regions, and it did not explore item memory at a more general level. To fill these gaps, this article reanalyzed data from the previous report, aiming to examine the neural correlates of item memory during encoding in early childhood (4-8 years) and interactions between the hippocampus and fronto-parietal regions during encoding. Consistent with research in older individuals, both the hippocampus and fronto-parietal regions were found to participate in item memory encoding. Additionally, functional connectivity between hippocampus and fronto-parietal regions was significantly related to both subsequent item memory and subsequent source memory. Taken together, these findings suggest that not only the activation of individual brain regions (hippocampus and fronto-parietal regions) but also the functional connections between these regions are important for memory encoding. These data add to the growing literature providing insight into how the hippocampus and cortical regions interact to support memory during development.

Boosting confidence without boosting performance: item strength creates the illusion of source accuracy.

People often express high confidence for misremembered sources. Starns and Ksander ([2016]. Item strength influences source confidence and alters source memory zROC slopes. Journal of Experimental Psychology: Learning, Memory, and Cognition, 42(3), 351-365; hereafter SK16) found that this happens more often when a person is highly confident in memory for the item itself, and that simply increasing item memory can increase high-confidence source errors. Under the decision heuristic account, this pattern emerges because strong item memories contaminate source judgments by promoting high confidence responses even when source evidence is relatively weak. Consequently, strengthening item memory is predicted to increase confidence for both correct and incorrect source responses; however, SK16 could not assess this key prediction because their item-strength manipulation also impaired source memory. We report two experiments with new item-strengthening manipulations designed to minimise source memory impairments. Results replicated the evidence for the decision heuristic account reported by SK16 and provided additional support by showing a boost in source confidence for both correct and error responses when item memory was strengthened without accompanying source impairments .

Better memory for emotional sources? A systematic evaluation of source valence and arousal in source memory.

Emotion-enhanced memory (EEM) describes the robust memory advantage of emotional over non-emotional stimuli. While extensively investigated with emotional items, it is unclear whether the EEM effect extends to source memory for a neutral item's emotional context. In two pre-registered studies, we systematically manipulated source valence (positive, negative) between participants and source arousal (high, low, neutral-low) within participants. In Experiment 1 (lab study, N = 80), we used emotional sound sources and presented them together with neutral pictures as items. In Experiment 2 (online study, N = 172), we used emotional background pictures with superimposed neutral item words to similarly manipulate source emotionality. Multinomial model-based analysis showed no general effects of valence or arousal on source memory across both experiments. Source memory was impaired for the negative high-arousing source in Experiment 1 but this did not replicate in Experiment 2. Altogether, we conclude that there are no memory-enhancing effects of source emotionality (valence, arousal, or any specific combination thereof) on source memory, dissociating emotionality effects between source and item memory. Additionally, we propose that material-dependent influences carry more weight if the used emotional material is limited in number, as is the case in the standard source-monitoring paradigm employing few sources only.

Pattern Separation and Source Memory Engage Distinct Hippocampal and Neocortical Regions during Retrieval.

Detailed representations of past events rely on the ability to form associations between items and their contextual features (i.e., source memory), as well as the ability to distinctly represent a new event from a similar one stored in memory (i.e., pattern separation). These processes are both known to engage the hippocampus, although whether they share similar mechanisms remains unclear. It is also unknown if, and in which region(s), activity related to these processes overlaps and/or interacts. Here, we used high-resolution fMRI to examine the contributions of hippocampal subfields and neocortical areas to pattern separation and source memory with an experimental paradigm that concurrently tested both. During encoding, male and female human subjects incidentally studied items in one of four quadrants on the screen. During test, they viewed repeated items (targets), similar items (lures), and new items (foils) and were asked to indicate whether each item was old, similar, or new. Following each item judgment, subjects were asked to indicate the quadrant in which the original stimulus was presented. Thus, each lure trial had a lure discrimination component (taxing pattern separation) and a location judgment (source memory). We found two main response profiles: (1) pattern separation-related signals in DG/CA3 and perirhinal cortex and (2) source memory signals in posterior CA1, parahippocampal cortex, and angular gyrus. Whole-brain voxelwise analysis revealed that activity related to lure discrimination and source memory was largely nonoverlapping. These findings suggest that distinct processes underlie the retrieval of pattern separated item representations and recollection of source information.SIGNIFICANCE STATEMENT Recalling past events with detail and accuracy depends on the ability to remember the contextual features of an event (i.e., source memory) as well as the ability to distinguish among similar events in memory (i.e., pattern separation). Previous work has shown that these processes are behaviorally dissociable (e.g., people can have clear memory for context but misidentify people or items). However, both processes engage the hippocampus, and it is unclear whether they rely on shared or distinct neural mechanisms. Here, we used high-resolution fMRI to concurrently assess hippocampal and neocortical activity related to source memory and pattern separation. We found that activity related to these processes was largely nonoverlapping, shedding light on two complementary but distinct mechanisms supporting episodic memory.