Prioritized memory access explains planning and hippocampal replay.

To make decisions, animals must evaluate candidate choices by accessing memories of relevant experiences. Yet little is known about which experiences are considered or ignored during deliberation, which ultimately governs choice. We propose a normative theory predicting which memories should be accessed at each moment to optimize future decisions. Using nonlocal 'replay' of spatial locations in hippocampus as a window into memory access, we simulate a spatial navigation task in which an agent accesses memories of locations sequentially, ordered by utility: how much extra reward would be earned due to better choices. This prioritization balances two desiderata: the need to evaluate imminent choices versus the gain from propagating newly encountered information to preceding locations. Our theory offers a simple explanation for numerous findings about place cells; unifies seemingly disparate proposed functions of replay including planning, learning, and consolidation; and posits a mechanism whose dysfunction may underlie pathologies like rumination and craving

Formation of a morphine-conditioned place preference does not change the size of evoked potentials in the ventral hippocampus–nucleus accumbens projection

Abstract In opioid addiction, cues and contexts associated with drug reward can be powerful triggers for drug craving and relapse. The synapses linking ventral hippocampal outputs to medium spiny neurons of the accumbens may be key sites for the formation and storage of associations between place or context and reward, both drug-related and natural. To assess this, we implanted rats with electrodes in the accumbens shell to record synaptic potentials evoked by electrical stimulation of the ventral hippocampus, as well as continuous local-field-potential activity. Rats then underwent morphine-induced (10 mg/kg) conditioned-place-preference training, followed by extinction. Morphine caused an acute increase in the slope and amplitude of accumbens evoked responses, but no long-term changes were evident after conditioning or extinction of the place preference, suggesting that the formation of this type of memory does not lead to a net change in synaptic strength in the ventral hippocampal output to the accumbens. However, analysis of the local field potential revealed a marked sensitization of theta- and high-gamma-frequency activity with repeated morphine administration. This phenomenon may be linked to the behavioral changes—such as psychomotor sensitization and the development of drug craving—that are associated with chronic use of addictive drugs

Neural processes mediating contextual influences on human choice behaviour

Contextual influences on choice are ubiquitous in ecological settings. Current evidence suggests that subjective values are normalized with respect to the distribution of potentially available rewards. However, how this context-sensitivity is realised in the brain remains unknown. To address this, here we examine functional magnetic resonance imaging (fMRI) data during performance of a gambling task where blocks comprise values drawn from one of two different, but partially overlapping, reward distributions or contexts. At the beginning of each block (when information about context is provided), hippocampus is activated and this response is enhanced when contextual influence on choice increases. In addition, response to value in ventral tegmental area/substantia nigra (VTA/SN) shows context-sensitivity, an effect enhanced with an increased contextual influence on choice. Finally, greater response in hippocampus at block start is associated with enhanced context sensitivity in VTA/SN. These findings suggest that context-sensitive choice is driven by a brain circuit involving hippocampus and dopaminergic midbrain

Significance of Input Correlations in Striatal Function

The striatum is the main input station of the basal ganglia and is strongly associated with motor and cognitive functions. Anatomical evidence suggests that individual striatal neurons are unlikely to share their inputs from the cortex. Using a biologically realistic large-scale network model of striatum and cortico-striatal projections, we provide a functional interpretation of the special anatomical structure of these projections. Specifically, we show that weak pairwise correlation within the pool of inputs to individual striatal neurons enhances the saliency of signal representation in the striatum. By contrast, correlations among the input pools of different striatal neurons render the signal representation less distinct from background activity. We suggest that for the network architecture of the striatum, there is a preferred cortico-striatal input configuration for optimal signal representation. It is further enhanced by the low-rate asynchronous background activity in striatum, supported by the balance between feedforward and feedback inhibitions in the striatal network. Thus, an appropriate combination of rates and correlations in the striatal input sets the stage for action selection presumably implemented in the basal ganglia

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

Interaction between hippocampal and striatal systems predicts subsequent consolidation of motor sequence memory.

The development of fast and reproducible motor behavior is a crucial human capacity. The aim of the present study was to address the relationship between the implementation of consistent behavior during initial training on a sequential motor task (the Finger Tapping Task) and subsequent sleep-dependent motor sequence memory consolidation, using functional magnetic resonance imaging (fMRI) and total sleep deprivation protocol. Our behavioral results indicated significant offline gains in performance speed after sleep whereas performance was only stabilized, but not enhanced, after sleep deprivation. At the cerebral level, we previously showed that responses in the caudate nucleus increase, in parallel to a decrease in its functional connectivity with frontal areas, as performance became more consistent. Here, the strength of the competitive interaction, assessed through functional connectivity analyses, between the caudate nucleus and hippocampo-frontal areas during initial training, predicted delayed gains in performance at retest in sleepers but not in sleep-deprived subjects. Moreover, during retest, responses increased in the hippocampus and medial prefrontal cortex in sleepers whereas in sleep-deprived subjects, responses increased in the putamen and cingulate cortex. Our results suggest that the strength of the competitive interplay between the striatum and the hippocampus, participating in the implementation of consistent motor behavior during initial training, conditions subsequent motor sequence memory consolidation. The latter process appears to be supported by a reorganisation of cerebral activity in hippocampo-neocortical networks after sleep