Brief memory reactivations induce learning in the numeric domain

Learning of arithmetic facts such as the multiplication table requires time-consuming, repeated practice. In light of evidence indicating that reactivation of encoded memories can modulate learning and memory processes at the synaptic, system and behavioral levels, we asked whether brief memory reactivations can induce human learning in the numeric domain. Adult participants performed a novel number-fact retrieval task in which they learned arbitrary numeric facts. Following encoding and a baseline test, 3 passive, brief reactivation sessions of only 40 seconds each were conducted on separate days. Learning was evaluated in a retest session. Results showed reactivations induced learning, with improved performance at retest relative to baseline test. Furthermore, performance was superior compared to a control group performing test-retest sessions without reactivations, who showed significant memory deterioration. A standard practice group completed active-retrieval sessions on 3 separate days, and showed significant learning gains. Interestingly, while these gains were higher than those of the reactivations group, subjects showing reactivation-induced learning were characterized by superior efficiency relative to standard practice subjects, with higher rate of improvement per practice time. A follow-up long-term retention experiment showed that 30 days following initial practice, weekly brief reactivations reduced forgetting, with participants performing superior to controls undergoing the same initial practice without reactivations. Overall, the results demonstrate that brief passive reactivations induce efficient learning and reduce forgetting within a numerical context. Time-efficient practice in the numeric domain carries implications for enhancement of learning strategies in daily-life settings, including in learning disorders caused by neurological conditions

Modulating temporal dynamics of performance across retinotopic locations enhances the generalization of perceptual learning

Summary: Human visual perception can be improved through perceptual learning. However, such learning is often specific to stimulus and learning conditions. Here, we explored how temporal dynamics of performance across conditions impact learning generalization. Participants performed a visual task, with the target at retinotopic location A. Then, the target was presented at location B either immediately after location A (same-session performance) or following a 48h consolidation period (different-session performance). Long-term generalization was measured the following week. Following initial training, both groups demonstrated generalization, consistent with previous accounts of fast learning. However, long-term generalization was enhanced in the same-session performance group. Consistently, improvements at locations A and B were correlated only following same-session performance, implying an integrated learning process across locations. The results support a new account of perceptual learning and generalization dynamics, suggesting that the temporal proximity of learning and consolidation of different conditions may integrate correlated learning processes, facilitating generalized learning

Modulating reconsolidation:a link to causal systems-level dynamics of human memories

A vital property of the brain is its plasticity, which manifests as changes in behavioral performance. Invasive studies at the cellular level in animal models reveal time-restricted windows during which existing memories that are reactivated become susceptible to modification through reconsolidation, and evidence suggests similar effects in humans. In this review, we summarize recent work utilizing noninvasive brain stimulation in humans to uncover the systems-level mechanisms underlying memory reconsolidation. This novel understanding of memory dynamics may have far reaching clinical implications, including the potential to modulate reconsolidation in patients with memory disorders

Causal role of prefrontal cortex in strengthening of episodic memories through reconsolidation

SummaryMemory consolidation is a dynamic process. Reactivation of consolidated memories triggers reconsolidation, a time-limited period during which memories can be modified [1–4]. Episodic memory refers to our ability to recall specific past events about what happened, including where and when [5]. However, it is unknown whether noninvasive stimulation of the neocortex during reconsolidation might strengthen existing episodic memories in humans. To modify these memories, we applied repetitive transcranial magnetic stimulation (rTMS) [6] over right lateral prefrontal cortex (PFC), a region involved in the reactivation of episodic memories [7, 8]. We report that rTMS of PFC after memory reactivation strengthened verbal episodic memories, an effect documented by improved recall 24 hr postreactivation compared to stimulation of PFC without reactivation and vertex (control site) after reactivation. In contrast, there was no effect of stimulation 1 hr postreactivation (control experiment), showing that memory strengthening is time dependent, consistent with the reconsolidation theory. Thus, we demonstrated that right lateral PFC plays a causal role in strengthening of episodic memories through reconsolidation in humans. Reconsolidation may serve as an opportunity to modify existing memories with noninvasive stimulation of a critical brain region, an issue of fundamental importance for memory research and clinical applications

Intrusive memories : A mechanistic signature for emotional memory persistence

Memories of negative emotional events persist more over time relative to memories for neutral information. Such persistence has been attributed to heightened encoding and consolidation processes. However, reactivation of the encoded information may also lead to reduced memory decay through rehearsal or a reconsolidation processes. Here, we tested whether involuntary intrusive memories, spontaneously arising following a stressful event and reactivating its memory, function to prevent memory decay, enhancing its persistence. Participants watched a stressful film containing scenes of aversive material. Memory for the film contents was tested immediately post film using a visual recognition test. In the following five days, participants recorded intrusive memories of the film using a digitized diary. After 5-days, memory for the film contents was retested. Results indicate that in the immediate aftermath of film watching, participant's memory scores were similarly high for scenes that were later experienced as intrusions and scenes that did not intrude, suggesting effective encoding for all scenes. However, persistence of memory for scenes that intruded was preserved relative to memory for scenes that did not intrude, pointing to a mechanism through which negative intrusive memories persist over time. Implications for memory modification interventions in trauma-related psychopathology are discussed

A Rapid Form of Offline Consolidation in Skill Learning

The brain strengthens memories through consolidation, defined as resistance to interference (stabilization) or performance improvements between the end of a practice session and the beginning of the next (offline gains) [1]. Typically, consolidation has been measured hours or days after the completion of training [2], but the same concept may apply to periods of rest that occur interspersed in a series of practice bouts within the same session. Here, we took an unprecedented close look at the within-seconds time course of early human procedural learning over alternating short periods of practice and rest that constitute a typical online training session. We found that performance did not markedly change over short periods of practice. On the other hand, performance improvements in between practice periods, when subjects were at rest, were significant and accounted for early procedural learning. These offline improvements were more prominent in early training trials when the learning curve was steep and no performance decrements during preceding practice periods were present. At the neural level, simultaneous magnetoencephalo-graphic recordings showed an anatomically defined signature of this phenomenon. Beta-band brain oscillatory activity in a predominantly contralateral frontoparietal network predicted rest-period performance improvements. Consistent with its role in sensorimotor engagement [3], modulation of beta activity may reflect replay of task processes during rest periods. We report a rapid form of offline consolidation that substantially contributes to early skill learning and may extend the concept of consolidation to a time scale in the order of seconds, rather than the hours or days traditionally accepted