No abstract

The characterization of the relationship between predictions and one-shot episodic encoding poses an important challenge for memory research. On the one hand, events that are compatible with our previous knowledge are thought to be remembered better than incompatible ones. On the other hand, unexpected situations, by virtue of their novelty, are known to cause enhanced learning. Several theoretical accounts try to solve this apparent paradox by conceptualizing prediction error (PE) as a continuum ranging from low PE (for expectation-matching events) to high PE (for expectation-mismatching ones). Under such a framework, the relationship between PE and memory encoding would be described by a U-shape function with higher memory performance for extreme levels of PE and lower memory for middle levels of PE. In this study, we tested the framework by using a gradual manipulation of the strength of association between scenes and objects to render different levels of PE and then tested for item memory of the (mis)matching events. In two experiments, in contrast to what was anticipated, recognition memory for object identity followed an inverted U-shape as a function of PE, with higher performance for intermediate levels of PE. Furthermore, in two additional experiments, we showed the relevance of explicit predictions at encoding to reveal such an inverted U pattern, thus providing the boundary conditions of the effect. We discussed our findings in light of existing literature relating PE and episodic memory, pointing out the potential roles of uncertainty in the environment, and the importance of the cognitive operations underlying encoding tasks.

The ability to learn sequential contingencies of actions for predicting future outcomes is indispensable for flexible behavior in many daily decision-making contexts. It remains open whether such ability may be enhanced by transcranial direct current stimulation (tDCS). The present study combined tDCS with functional near-infrared spectroscopy (fNIRS) to investigate potential tDCS-induced effects on sequential decision-making and the neural mechanisms underlying such modulations. Offline tDCS and sham stimulation were applied over the left and right dorsolateral prefrontal cortex (dlPFC) in young male adults (N = 29, mean age = 23.4 years, SD = 3.2) in a double-blind between-subject design using a three-state Markov decision task. The results showed (i) an enhanced dlPFC hemodynamic response during the acquisition of sequential state transitions that is consistent with the findings from a previous functional magnetic resonance imaging (fMRI) study; (ii) a tDCS-induced increase of the hemodynamic response in the dlPFC, but without accompanying performance-enhancing effects at the behavioral level; and (iii) a greater tDCS-induced upregulation of hemodynamic responses in the delayed reward condition that seems to be associated with faster decision speed. Taken together, these findings provide empirical evidence for fNIRS as a suitable method for investigating hemodynamic correlates of sequential decision-making as well as functional brain correlates underlying tDCS-induced modulation. Future research with larger sample sizes for carrying out subgroup analysis is necessary in order to decipher interindividual differences in tDCS-induced effects on sequential decision-making process at the behavioral and brain levels.

The characterization of the relationship between predictions and one-shot episodic encoding poses an important challenge for memory research. On the one hand, events that are compatible with our previous knowledge are thought to be remembered better than incompatible ones. On the other hand, unexpected situations, by virtue of their surprise, are known to cause enhanced learning. Several theoretical accounts try to solve this apparent paradox by conceptualizing prediction error (PE) as a continuum ranging from low PE (for expectation matching events) to high PE (for expectation mismatching ones). Under such framework, the relationship between PE and memory encoding would be described by a U-shape function with higher memory performance for extreme levels of PE and lower memory for middle levels of PE. In this study we used a gradual manipulation of the strength of association between scenes and objects to render different levels of PE and then tested for episodic memory of the (mis)matching events. In two experiments, and in contrast to what was anticipated, recognition memory as a function of PE followed an inverted U-shape, with higher performance for intermediate levels of PE. Furthermore, in two additional experiments we showed the relevance of explicit predictions at encoding to reveal such inverted U pattern, thus providing the boundary conditions of the effect. We discuss our current findings in the light of the uncertainty in the environment and the importance of the operations underlying encoding tasks.

Memory consolidation tends to be less robust in childhood than adulthood. However, little is known about the corresponding functional differences in the developing brain that may underlie age-related differences in retention of memories over time. This study examined system-level memory consolidation of object-scene associations after learning (immediate delay), one night of sleep (short delay), as well as two weeks (long delay) in 5-to-7-year-old children (n = 49) and in young adults (n = 39), as a reference group with mature consolidation systems. Particularly, we characterized how functional neural activation and reinstatement of neural patterns change over time, assessed by functional magnetic resonance imaging combined with representational (dis)similarity analysis (RSA). Our results showed that memory consolidation in children was less robust (i.e., more forgetting) compared to young adults. For correctly retained remote memories, young adults showed increased neural activation from short to long delay in neocortical (parietal, prefrontal and occipital) and cerebellar brain regions, while children showed increased neural activation in prefrontal and decrease in neural activity in parietal brain regions over time. In addition, there was an overall attenuated scene-specific memory reinstatement of neural patterns in children compared to young adults. At the same time, we observed category-based reinstatement in medial-temporal, neocortical (prefrontal and parietal), and cerebellar brain regions only in children. Taken together, 5-to-7-year-old children, compared to young adults, show less robust memory consolidation, possibly due to difficulties in engaging in differentiated neural reinstatement in neocortical mnemonic regions during retrieval of remote memories, coupled with relying more on gist-like, category-based neural reinstatement.

Childhood is a period when memory consolidation and knowledge base undergo rapid changes. The present study examined short-delay (overnight) and long-delay (after a 2-week-period) consolidation of new information either congruent or incongruent with prior knowledge in typically developing younger 6-to-8-year-old children (n = 32), older 9-to-11-year-old children (n = 33), and 18-to-30-year-old young adults (n = 39). Both memory accessibility (cued recall of objects) and precision (precision of objects placement) of initially well-learned object-scene pairs were measured. Our results showed that overnight, memory accessibility declined similarly in all age groups; memory precision improved more in younger children compared to older children and even declined in young adults. After a 2-week-period, both memory accessibility and precision became worse. Specifically, while age groups showed similar decline in memory accessibility, precision decline was less in younger children than in older children and young adults. The decline in accessibility and precision for incongruent information was particularly strong in adults. Taken together, our results showed that, for initially well-learned information, younger children have robust memory consolidation, despite their overall lower mnemonic performance compared to older children and young adults, which is potentially crucial for stable and precise knowledge accumulation early on in development.

No abstract

Human capacity to remember experienced episodes over a long period of time has its roots in childhood and develops throughout the lifespan. However, the neural regions supporting memory consolidation in the developing brain remain to be ascertained. The present study examined system-level memory consolidation of object-location associations after one night of sleep (short delay) and after two weeks (long delay), and its relation to structural brain measures in normally developing term born and preterm born 6-year-old children, as well as in young adults as a reference group of mature consolidation systems. We showed that final learning performance was reduced in preterm in comparison to term born children, who in turn were outperformed by young adults. There were no differences in short- and long-delay memory consolidation between term and preterm born children. Despite comparable short-delay memory consolidation in all groups, both term and preterm born children showed less efficient long-delay memory consolidation in comparison to young adults. Moreover, long-delay memory consolidation was positively associated with larger hippocampal volume in children, while a thinner medial orbitofrontal cortex was associated with better overall memory retention rates in all age groups. Thinner medial orbitofrontal cortex was furthermore associated with higher final learning performance in children. Taken together, the results suggest that temporal dynamics of memory consolidation and its association with structural brain measures in 6-year-old term born and preterm born children are comparable but differ from young adults.