Unintentional and intentional recognition rely on dissociable neurocognitive mechanisms

Distractibility can lead to accidents and academic failures, as well as memory problems. Recent evidence suggests that intentional recognition memory can be biased by unintentional recognition of distracting stimuli in the same environment. It is unknown whether unintentional and intentional recognition depend on the same underlying neurocognitive mechanisms. We assessed whether human participants’ recognition of previously seen (old) or not seen (new) target stimuli was affected by whether a to-be-ignored distractor was old or new. ERPs were recorded to investigate the neural correlates of this bias. The results showed that the old/new status of salient distractors had a biasing effect on target recognition accuracy. Both intentional and unintentional recognition elicited early ERP effects that are thought to reflect relatively automatic memory processes. However, only intentional recognition elicited the later ERP marker of conscious recollection, consistent with previous suggestions that recollection is under voluntary control. In contrast, unintentional recognition was associated with an enhanced late posterior negativity, which may reflect monitoring or evaluation of memory signals. The findings suggest that unintentional and intentional recognition involve dissociable memory processes

Expectations modulate early but not late event-related potential correlates of successful recognition memory

textRecognizing that an item has been previously encountered may not only depend on the strength of memory for that item, but also the expectation that the item will be remembered. Recent studies by O’Connor, et al (2010) and Jaeger et al (2013) revealed that a significant portion of the functional magnetic resonance imaging (fMRI) “retrieval success” effect (BOLD signal for correctly identified old items > new items) depends upon whether participants expect novel or familiar stimuli. The current study examined how expectancy modulates the event-related potential (ERP) retrieval success effect. We employed a typical recognition memory task with the addition of explicit cues indicating if upcoming memory probes were “likely old”, “likely new” (with 75% validity), or “unknown”. An electrophysiological response to the cue, primarily across frontal electrodes from 700-850ms after cue onset, predicted individual differences in cue- induced bias in memory judgments. Responses to memory probes were examined 300- 400ms and 500-700ms after probe onset, corresponding to time windows previously associated with ERP correlates of memory processing. Differences between old and new items were greatest from 300-400ms when preceded by “likely old” cues, overlapping with a component previously identified as tracking familiarity-based processing. In contrast, the 500-700ms time window, previously associated with recollection, revealed significant differences between old and new items that were not modulated by cue type. Overall this pattern of results shows that cue induced biases influence earlier (300-400ms after onset of a memory probe) but not later retrieval processing (500-700ms).Psycholog

Counterfactual imagination impairs memory for true actions: EEG and behavioural evidence

Imagined events can be misremembered as experienced, leading to memory distortions. However, less is known regarding how imagining counterfactual versions of past events can impair existing memories. We addressed this issue, and used EEG to investigate the neurocognitive processes involved when retrieving memories of true events that are associated with a competing imagined event. Participants first performed simple actions with everyday objects (e.g., rolling dice). A week later, they were shown pictures of some of the objects and either imagined the same action they had originally performed, or imagined a counterfactual action (e.g., stacking the dice). Subsequent tests showed that memory for performed actions was reduced after counterfactual imagination when compared to both veridical imagination and a baseline condition that had not been imagined at all, providing novel evidence that counterfactual imagination impairs true memories beyond simple forgetting over time. ERPs and EEG oscillations showed evidence of separate processes associated with memory retrieval versus post-retrieval processes that were recruited to support recall of memories that were challenging to access. The findings show that counterfactual imagination can cause impairments to sensorimotor-rich event memories, and provide new evidence regarding the neurocognitive mechanisms that are recruited when people need to distinguish memories of imagined versus true events

Spatiotemporal pattern of brain electrical activity related to immediate and delayed episodic memory retrieval

In the present study we used the event-related brain potentials (ERP) technique and eLORETA (exact low-resolution electromagnetic tomography) method in order to characterize and compare the performance and the spatiotemporal pattern of the brain electrical activity related to the immediate episodic retrieval of information (words) that is being learned relative to delayed episodic retrieval twenty-minutes later. For this purpose, 16 young participants carried out an old/new word recognition task with source memory (word colour). The task included an immediate memory phase (with three study-test blocks) followed (20 min later) by a delayed memory phase with one test block. The behavioural data showed progressive learning and consolidation of the information (old words) during the immediate memory phase. The ERP data to correctly identified old words for which the colour was subsequently recollected (H/H) compared to the correctly rejected new words (CR) showed: (1) a significant more positive-going potential in the 500–675 ms post-stimulus interval (parietal old/new effect, related to recollection), and (2) a more negative-going potential in the 950–1850 ms interval (LPN effect, related to retrieval and post-retrieval processes). The eLORETA data also revealed that the successful recognition of old words (and probably retrieval of their colour) was accompanied by activation of (1) left medial temporal (parahippocampal gyrus) and parietal regions involved in the recollection in both memory phases, and (2) prefrontal regions and the superior temporal gyrus (in the immediate and delayed memory phases respectively) involved in monitoring, evaluating and maintaining the retrieval products. These findings indicate that episodic memory retrieval depends on a network involving medial temporal lobe and frontal, parietal and temporal neocortical structures. That network was involved in immediate and delayed memory retrieval and during the course of memory consolidation, with greater activation of some nodes (mobilization of more processing resources) for the delayed respect to the immediate retrieval conditionThis study was supported by grants from the Spanish Government, Ministerio de Ciencia e Innovación (PSI2014-55316-C3-3-R; PSI2017-89389-C2-2-R), with FEDER Funds; the Galician Government, Consellería de Cultura, Educación e Ordenación Universitaria, Axudas para a Consolidación e Estruturación de Unidades de Investigación Competitivas do Sistema Universitario de Galicia: GRC (GI-1807-USC); Ref: ED431-2017/27, with FEDER fundsS

Effects of Saccade Induced Retrieval Enhancement on Conceptual and Perceptual Tests of Explicit & Implicit Memory

The effects of saccadic horizontal (bilateral) eye movements upon tests of both conceptual and perceptual forms of explicit and implicit memory were investigated. Participants studied a list of words and were then assigned to one of four test conditions: conceptual explicit, conceptual implicit, perceptual explicit, or perceptual implicit. Conceptual tests comprised category labels with either explicit instructions to recall corresponding examples from the study phase (category-cued recall), or implicit instructions to generate any corresponding examples that spontaneously came to mind (category-exemplar generation). Perceptual tests comprised of word-fragments with either explicit instructions to complete these with study items (word-fragment-cued recall), or implicit instructions to complete each fragment with the first word that simply ‘popped to mind’ (word-fragment completion). Just prior to retrieval, participants were required to engage in 30s of bilateral vs. no eye movements. Results revealed that saccadic horizontal eye movements enhanced performance in only the conceptual explicit condition, indicating that Saccade-Induced Retrieval Enhancement is a joint function of conceptual and explicit retrieval mechanisms. Findings are discussed from both a cognitive and neuropsychological perspective, in terms of their potential functional and neural underpinnings

Is Face Recognition Biased by Unintentional Recognition of Distracting Information?

Research highlights that we are not as skilful in controlling our memory as we may believe. Instead, our everyday intentional recognition judgments are often biased by what we unintentionally recognise in the same context. So far, it has been demonstrated that the unintentional recognition of image distractors can bias the intentional recognition of word targets, in the form of a familiarity (old/new) congruency bias. This bias reflects improved recognition performance for targets when the distractor/context upon which it is present at test is of the same memory status (also old or new). However, this effect has not yet been explored using face stimuli, despite faces varying in pre-existing familiarity and often being encountered in different familiar or unfamiliar contexts in everyday life. Furthermore, the distractor stimuli used in past literature have often been limited to simple drawings. Past designs have also typically relied on the use of working memory load or divided-attention tasks, or healthy aging to magnify distractibility, which is arguably not ecological valid nor generalisable. Consequently, this research investigated whether distractor-induced congruency biases found for words also apply to faces, using a new database of up-to-date face stimuli and without secondary manipulations of distractibility. I also attempted to replicate these results in an alternative sample and compared effects between target types (words vs faces). Results show novel evidence for the idea that faces are also biased by distracting stimuli in the same manner that has been found in relation to words. In turn, providing evidence for specific cognitive theories (e.g. Perceptual load theory) while questioning others (face processing modularity). Lastly, the study also provides future direction for neurocognitive research to answer questions regarding the underlying mechanisms of distractor bias, based on past research findings of dissociating event-related potentials (ERPs) in relation to unintentional and intentional recognition

Multimodal imaging reveals the spatiotemporal dynamics of recollection.

Functional MRI research suggests that different frontal and parietal cortical regions support strategic processes that are engaged at different stages of recollection, from pre-retrieval processing of a cue to post-retrieval maintenance and evaluation of recollected information. Whereas some of these regions respond in a domain-general way, other regions are sensitive to the type of information being recollected. However, the low temporal resolution of fMRI cannot distinguish component processes at the time-scale at which recollection occurs. We therefore combined fMRI with the excellent temporal resolution of source localised EEG/MEG to investigate the spatiotemporal neural dynamics of recollection. fMRI and EEG/MEG data were collected from the same participants in two sessions while they retrieved different types of episodic information. This multimodal imaging approach revealed striking consistency between the regions identified with fMRI and EEG/MEG, providing novel evidence of how these brain areas interact over time to support source recollection. For domain-general recollection, results from both modalities converged in showing the strongest activations in medial parietal cortex, which according to EEG/MEG was reliable at a late retrieval stage. Domain-specific source recollection increased fMRI and EEG/MEG activation in the left lateral prefrontal cortex, which EEG/MEG indicated also to be recruited during a post-recollection stage. The findings suggest that although medial parietal and left lateral prefrontal regions mediate functionally different retrieval processes, they are both engaged at a late stage of episodic retrieval

The contributions of sleep-related consolidation to emotional item and associative memory.

Extant empirical evidence of the past two decades suggests a pivotal role of sleep in system consolidation of episodic memory. Models of active system consolidation (Diekelmann & Born, 2010; Rasch & Born, 2013) propose that periods of restricted sensory processing that are pervasive during slow wave sleep (SWS) provide the opportunity of coordinated reactivations. These reactivations are assumed to result in subsequent redistribution of memory representations from intermediate maintenance in the hippocampus toward long-term storage in neocortical networks. However, newly emerging evidence (Genzel, Spoormaker, Konrad, & Dresler, 2015; Hutchison & Rathore, 2015) indicates that a consolidation process, which is highly distinct from the former framework, unfolds across periods of rapid eye movement (REM) sleep, fostering the selective enhancement of emotional memory retrieval. Critically, the interactions of both processes with regard to emotional associative memory have remained largely unexplored at present. This motivated the objectives of the present thesis, which aimed to generate a more comprehensive understanding of the differential contributions of consolidation processes during SWS and REM sleep to (non-)emotional item and associative memory retention. This was addressed in two consecutive experiments, which examined behavioral performance changes across different intervals of sleep, and aimed to link these to specific oscillatory features of SWS (sleep spindle activity) and REM sleep (right-frontal theta lateralization). In experiment 1 consolidation processes were studied in a split-night-design, which contrasts the effects of early night sleep (entailing high amounts of SWS) with those of late night sleep (which is predominated by REM sleep episodes). In order to dissociate item memory from distinct retrieval of contextual features, participants performed a source memory task that ascertained the accurate recognition of (non-)emotional images, as well as the accurate retrieval of the initial screen location (right or left) during encoding. Analyses revealed a significant consolidation benefit for emotional images with regard to item recognition, irrespective of sleep. Source memory performance was differentially modulated across early and late night sleep as a function of stimulus valence. While early night sleep was associated with a selective retention benefit for neutral source memory, late night sleep yielded a selective benefit to emotional source recognition across sleep. This dissociation was further substantiated on a neurophysiological level, by means of selective correlations between spindle power (SWS) and neutral memory performance in the early sleep group, which was complimented by a selective association between right-frontal theta laterality (REM sleep), and emotional source recognition in the late sleep group. As such, the results of experiment 1 genuinely revealed dissociable processes related to the consolidation of emotional and neutral source memory emerging across sleep. Moreover, this extends prior conceptions (Spoormaker, Czisch, & Holsboer, 2013) of consolidation processes during REM sleep, as these were believed to be confined to item memory reprocessing. Experiment 2 attempted to address the generalizability of these previous findings with regard to the critical timing and duration of these consolidation processes, as well as concerning the effects of perceptual integration processes at the encoding stage. In order to examine performance changes across a restricted sleep interval entailing high proportions of REM sleep, an early morning nap paradigm was employed in which participants were randomly allocated to a wakeful control condition or to a 120-minute nap sleep condition in the early morning hours. As previous effects with regard to REM sleep (experiment 1) may be bound to certain preconditions at encoding (Murray & Kensinger, 2012), specifically to the inherent level of perceptual integration between emotional items and source features, experiment 2 adopted a different approach requiring the active integration of both components at the encoding stage. To this end, item and associative recognition were probed by means of a paired-associates task, which required the accurate retrieval of arbitrary object-scene-associations (entailing emotional or neutral scenes) formed during the encoding phase. Analyses yielded a selective, sleep-related retention benefit in associative recognition for both stimulus categories. However, this benefit in performance was again partially dissociable on a neurophysiological level as evident by selective correlations between spindle density during non-rapid eye movement (NREM) sleep and neutral associative memory performance. These results reinforce the former findings of experiment 1, demonstrating that similar consolidation effects related to SWS and REM sleep can be retained on a behavioral level after a brief interval of sleep during the daytime and in a dissimilar task design, requiring active integration of item and context at encoding. However, the lack of a robust correlation with regard to right-frontal theta lateralization signifies that the circadian modulations and neurophysiological specifics of REM sleep, place certain restrictions on the accurate assessment of related processes in diurnal nap paradigms. In summary, the present thesis constitutes a first systematic approach towards dissociating the contributions of REM sleep and SWS to emotional associative memory consolidation, across two consecutive but dissimilar study designs. The yielded findings originally suggest that consolidation processes during both sleep stages are dissociable, but beyond this, contribute independently to memory retention of emotional and neutral associations. This was also substantiated on a neurophysiological level with regard to selective correlations between oscillatory features of both sleep stages and memory performance. Moreover, in support of previous conceptions (Hutchison & Rathore, 2015), it was genuinely established that REM sleep exhibits the unique capacity to influence associative memory of emotional stimuli. The exact mechanism by which this is accomplished remains to be elucidated in future experiments.Eine Vielzahl empirischer Befunde der letzten zwei Jahrzehnte belegen, dass der Schlaf eine tiefgreifende Rolle in der Gedächtniskonsolidierung zwischen unterschiedlichen Gedächtnissystems einnimmt. Sukzessive verfeinerte Modelle über aktive Vorgänge der „Systemkonsolidierung“ (Diekelmann & Born, 2010; Rasch & Born, 2013) legen nahe, dass Phasen eingeschränkter sensorischer Verarbeitung, die über den Tiefschlaf hinweg dominieren, ein Zeitfenster bieten in dem Gedächtnisspuren im Hippocampus in koordinierter Weise reaktiviert werden können. Diese Reaktivierungen gehen mit einer Integration der jeweiligen Gedächtnisinhalte in neokortikalen Netzwerken einher, die eine langfristige Aufrechterhaltung des Gedächtnisabrufs ermöglichen. Neue Befunde (Genzel et al., 2015; Hutchison & Rathore, 2015) legen allerdings nahe, dass sich ein weiterer Konsolidierungsprozess über den Schlaf hinweg vollzieht, der zu einer selektiven Aufrechterhaltung emotionaler Gedächtnisinhalte beiträgt. Dieser Prozess ist wiederum assoziiert mit dem Auftreten von REM-Schlaf (REM, engl. Rapid Eye Movement) Episoden. Bislang ist jedoch unklar, wie beide Konsolidierungsprozesse über unterschiedliche Schlafstadien hinweg miteinander interagieren in Bezug auf das emotionale Assoziationsgedächtnis. Dies bildete den Ausgangspunkt der vorliegenden Arbeit, die ein umfassenderes Verständnis hinsichtlich der Beiträge unterschiedlicher Konsolidierungsprozesse im Tiefschlaf und REM Schlaf in der Aufrechterhaltung des (nicht-)emotionalen Item- und Assoziationsgedächtnisses anstrebt. Dies wurde in zwei aufeinander aufbauenden Experimenten näher beleuchtet, in denen behaviorale Leistungsveränderungen über unterschiedliche Schlafintervalle untersucht wurden mit dem Ziel diese mit spezifischen oszillatorischen Merkmalen des Tiefschlafs (Schlafspindel Aktivität) und des REM Schlafs (Rechts-frontale Theta Lateralisierung) in Verbindung zu bringen. In Experiment 1 wurden diese Konsolidierungsprozesse in einem „Split-night-design“ untersucht, das die Möglichkeit bietet, frühen Nachtschlaf (mit hoher Tiefschlafdauer) mit spätem Nachtschlaf (der von REM-Schlaf Episoden dominiert wird) zu kontrastieren. Um das Itemgedächtnis von dem distinkten Abruf kontextueller Merkmale dissoziieren zu können, wurde eine Quellengedächtnisaufgabe von den Probanden bearbeitet, in der sowohl das Wiedererkennen (nicht)emotionaler Bilder als auch der Abruf der initialen Bildschirmposition (rechts oder links) in der Lernphase erfasst wurde. Die berichteten Analysen weisen auf einen signifikanten Konsolidierungsvorteil für das Wiedererkennen emotionaler Bilder über die Zeit hinweg hin, der jedoch unabhängig vom Schlaf auftritt. Die Quellengedächtnisleistung wird hingegen differentiell über den frühen und späten Nachtschlaf in Abhängigkeit von der Stimulusvalenz aufrechterhalten. Während früher Nachtschlaf mit einer selektiven Aufrechterhaltung des neutralen Quellengedächtnisses assoziiert war, konnte der späte Nachtschlaf mit einer selektiven Erhaltung des emotionalen Quellengedächtnisses in Verbindung gebracht werden. Diese Dissoziation war darüber hinaus auf neurophysiologischer Ebene nachweisbar anhand selektiver Korrelationen zwischen der Spindelaktivität im Tiefschlaf und der neutralen Gedächtnisleistung über den frühen Nachtschlaf und einer selektiven Korrelation zwischen der rechts-frontalen Theta Lateralisierung im REM Schlaf und der emotionalen Quellengedächtnisleistung über den späten Nachtschlaf. Die Ergebnisse des ersten Experiments eröffnen eine neue Perspektive, indem sie die Existenz zweier dissoziierbarer Prozesse in der Konsolidierung des emotionalen und neutralen Quellengedächtnisses über den Schlaf hinweg nahelegen. Im Zuge dessen erweitern die vorliegenden Ergebnisse vorangegangene Konzepte (Spoormaker et al., 2013) der Gedächtniskonsolidierung im REM Schlaf, die bislang eine eingeschränkte Wirkung auf das Itemgedächtnis prädizierten. Das Ziel von Experiment 2 war es, diese neuen Ergebnisse auf ihre Generalisierbarkeit hin zu prüfen, insbesondere hinsichtlich der kritischen Zeitverlaufs und der Dauer der zugrundliegenden Konsolidierungsprozesse und in Bezug auf die Bedeutung perzeptueller Integrationsprozesse während der Enkodierphase. Um Veränderungen in der Gedächtnisleistung über ein kurzes Schlafintervall mit hohen REM-Schlaf-Anteilen zu untersuchen wurde ein Kurzschlaf Paradigma am frühen Morgen eingesetzt in dem Probanden einer Wachkontrollbedingung oder einer 120-minütigen Tagschlafbedingung am frühen Morgen zugewiesen wurden. Die vorangegangenen Ergebnisse aus Experiment 1 hinsichtlich der Effekte des REM-Schlafs könnten unter Zugrundelegung der Literatur (Murray & Kensinger, 2013) an bestimmte Bedingungen während er Enkodierungsphase gekoppelt sein, speziell an den inhärente Grad der perzeptuellen Integration zwischen emotionalen Items und ihren Quellenmerkmalen. Um dies zu prüfen wurde in Experiment 2 eine andere Herangehensweise mit einer Gedächtnisaufgabe, die eine aktive Integration beider Komponenten während der Enkodierung erforderlich machte, gewählt. Item- und Assoziationsgedächtnis wurden über das Behalten paarweise gelernter Assoziationen zwischen (nicht)emotionalen Bildern und Alltagsobjekten erfasst. Die korrespondierenden Analysen erbrachten einen selektiven, schlafbezogenen Vorteil in der Aufrechterhaltung der assoziativen Gedächtnisleistung über die Zeit hinweg in beiden Stimuluskategorien. Darüber hinaus war dieser Effekt erneut teilweise dissoziierbar auf neurophysiologischer Ebene, was sich in selektiven Korrelationen der Spindeldichte während des non-rapid eye movement (NREM) Schlafs zu der neutralen Assoziationsgedächtnisleistung wiederspiegelte. Diese Ergebnisse untermauern die vorangegangen Befunde aus Experiment 2, indem ähnliche Konsolidierungseffekte des Tiefschlafs und des REM Schlafs über ein kurzes Schlafintervall am frühen Morgen und innerhalb eines Aufgaben-Paradigmas, dass die aktive Integration während der Enkodierungsphase erforderte, auf behavioraler Ebene bestätigt werden konnten. Dennoch verweist das Ausbleiben einer robusten Korrelation zu der rechts-frontalen Theta Lateralisierung im REM-Schlaf darauf, dass zirkadiane Modulationen und neurophysiologische Besonderheiten des REM-Schlafs gewisse Begrenzungen in der akkuraten Erfassung dieser Prozesse innerhalb von Kurzschlaf-Paradigmen während des Tages setzen. Die vorliegende Arbeit stellt eine erste systematische Annäherung an eine Dissoziierung der Beiträge des Tiefschlafs und des REM-Schlafs in der Konsolidierung des emotionalen Assoziationsgedächtnisses dar, die über zwei aufeinander aufbauende aber unterschiedliche Studiendesigns hinweg angestrebt wurde. Die daraus hervorgegangenen Ergebnisse legen erstmals nahe, dass Konsolidierungsprozesse über beide Schlafstadien dissoziierbar sind aber darüber hinaus gehend eigenständig zu einer Aufrechterhaltung der Gedächtnisleistung für neutrale und emotionale Assoziationen beitragen. Dies konnte auch auf neurophysiologischer Ebene über selektive Korrelationen zu oszillatorischen Merkmalen beider Schlafstadien substantiiert werden. Darüber hinaus konnte erstmalig nachgewiesen werden, dass Prozesse während des REM Schlaf über die Kapazität verfügen auf das assoziative Erinnern emotionaler Inhalte einzuwirken in Übereinstimmung zu neueren theoretischen Konzepten (Hutchison & Rathore, 2015). Der genaue Mechanismus über den dies bewirkt wird muss in zukünftigen Experimenten näher beleuchtet werden