Auditory conditioned stimulus presentation during NREM sleep impairs fear memory in mice

Externally manipulating memories by presenting conditioned stimuli (CS) during sleep is a new approach to investigating memory processing during sleep. However, whether presenting a CS during REM or NREM sleep enhances or extinguishes fear memory has not been clearly delineated. In this study, mice underwent trace fear conditioning consisting of an auditory CS paired with a foot shock, and the auditory CS was re-presented during subsequent REM or NREM sleep. Mice that received auditory cueing during NREM but not REM sleep showed impaired fear memory upon later presentation of the auditory CS. These findings have implications for the use of cueing during sleep and advance our understanding of the role of REM and NREM sleep in memory consolidation.</p

Die Reaktivierung von Vokabeln an wachen Personen am Tag hat keinen Einfluss auf die Gedächtnisleistung

Background It is assumed that the beneficial effect of sleep on memory relies on spontaneous reactivation of memories during sleep. We recently showed that reactivation by re-exposure to previously learned foreign vocabulary cues during sleep benefits vocabulary learning. Cueing foreign vocabulary during active or passive wakefulness at night did not improve memory, suggesting that memory benefits of cueing are specific to sleep. However, the ineffectiveness of cueing during wakefulness might also be explained by increased tiredness of the participants in this former study. Objectives To exclude tiredness as a confounding factor, we tested the effect of vocabulary cueing during active and passive daytime wakefulness. It was hypothesized that cueing during waking does not improve memory consolidation, even when participants are well rested. Methods A total of 32 subjects learned 120 Dutch–German word pairs. During a 3 h retention interval, parts of the previously learned Dutch words were replayed. Subjects of the active waking group (N = 16) were distracted from hearing the Dutch words by an n-back task, while subjects of the passive waking group (N = 16) were not distracted. After the retention interval, memory for word pairs was tested by a cued recall. Results Replay of Dutch words during daytime wake did not improve later memory for the German translation in either of the waking groups. We observed no difference in recall performance between cued and uncued words, neither in the active waking nor in the passive waking group. Conclusion Cueing Dutch words during wakefulness does not exert beneficial effects on memory, even when subjects are well rested and under full control of their cognitive capacities. This result gives further evidence that the beneficial effects of cueing are solely specific to sleep. Zusammenfassung Hintergrund Es wird angenommen, dass die förderliche Wirkung von Schlaf auf die Gedächtniskonsolidierung auf spontanen Reaktivierungen zuvor gelernter Inhalte beruht. Wir konnten bereits zeigen, dass das Wiederabspielen zuvor gelernter holländischer Vokabeln im Schlaf zu einer verbesserten Gedächtnisleistung führt. Da dasselbe Vorgehen in einer aktiven und einer passiven Wachgruppe während der Nacht zu keiner Gedächtnisverbesserung führte, wurde die gedächtnisförderliche Wirkung des Wiederabspielens als schlafspezifisch interpretiert. Die fehlende Wirkung im Wachzustand könnte aber auch auf die erhöhte Müdigkeit der Versuchspersonen zurückzuführen sein. Ziel der Arbeit Um Müdigkeit als konfundierenden Faktor ausschließen zu können, wurden in der vorliegenden Studie die Effekte des Wiederabspielens zuvor gelernter holländischer Vokabeln während des Tages erfasst. Die Hypothese war, dass das Wiederabspielen im Wachzustand nicht zu einer Verbesserung des Gedächtnisses führt, selbst wenn die Probanden ausgeruht sind. Material und Methoden 32 Versuchspersonen lernten 120 deutsch-holländische Wortpaare. Während einer 3-stündigen Konsolidierungsphase wurden ihnen ein Teil der zuvor gelernten holländischen Wörter wieder vorgespielt. Versuchspersonen der aktiven Wachgruppe (N = 16) führten während des Hörens der Wörter eine n-Back-Aufgabe durch, während Versuchspersonen der passiven Wachgruppe (N = 16) nicht abgelenkt wurden. Im Anschluss wurde die Gedächtnisleistung für alle holländisch-deutschen Wortpaare geprüft. Ergebnisse Das wiederholte Abspielen der holländischen Wörter verbesserte nicht die Gedächtnisleistung für die deutschen Übersetzungen, weder in der aktiven noch in der passiven Wachgruppe. Diskussion Auch wenn Probanden ausgeruht sind, führt das Abspielen von holländischen Vokabeln zu keiner gedächtnisförderlichen Wirkung. Dieses Ergebnis ist ein weiterer Beleg für die Schlafspezifität der gedächtnisförderlichen Wirkung von Reaktivierungen auf die Gedächtnisbildung

Brief targeted memory reactivation during the awake state enhances memory stability and benefits the weakest memories

Abstract Reactivation of representations corresponding to recent experience is thought to be a critical mechanism supporting long-term memory stabilization. Targeted memory reactivation, or the re-exposure of recently learned cues, seeks to induce reactivation and has been shown to benefit later memory when it takes place during sleep. However, despite recent evidence for endogenous reactivation during post-encoding awake periods, less work has addressed whether awake targeted memory reactivation modulates memory. Here, we found that brief (50 ms) visual stimulus re-exposure during a repetitive foil task enhanced the stability of cued versus uncued associations in memory. The extent of external or task-oriented attention prior to re-exposure was inversely related to cueing benefits, suggesting that an internally-orientated state may be most permissible to reactivation. Critically, cueing-related memory benefits were greatest in participants without explicit recognition of cued items and remained reliable when only considering associations not recognized as cued, suggesting that explicit cue-triggered retrieval processes did not drive cueing benefits. Cueing benefits were strongest for associations and participants with the poorest initial learning. These findings expand our knowledge of the conditions under which targeted memory reactivation can benefit memory, and in doing so, support the notion that reactivation during awake time periods improves memory stabilization

Emotional arousal modulates oscillatory correlates of targeted memory reactivation during NREM, but not REM sleep

Rapid eye movement (REM) sleep is considered to preferentially reprocess emotionally arousing memories. We tested this hypothesis by cueing emotional vs. neutral memories during REM and NREM sleep and wakefulness by presenting associated verbal memory cues after learning. Here we show that cueing during NREM sleep significantly improved memory for emotional pictures, while no cueing benefit was observed during REM sleep. On the oscillatory level, successful memory cueing during NREM sleep resulted in significant increases in theta and spindle oscillations with stronger responses for emotional than neutral memories. In contrast during REM sleep, solely cueing of neutral (but not emotional) memories was associated with increases in theta activity. Our results do not support a preferential role of REM sleep for emotional memories, but rather suggest that emotional arousal modulates memory replay and consolidation processes and their oscillatory correlates during NREM sleep