Memory Consolidation Processes Research Articles

Brain Arrhythmias Induced by Amyloid Beta and Inflammation: Involvement in Alzheimer's Disease and Other Inflammation-related Pathologies.

A variety of neurological diseases, including Alzheimer's disease (AD), involve amyloid beta (Aβ) accumulation and/or neuroinflammation, which can alter synaptic and neural circuit functions. Consequently, these pathological conditions induce changes in neural network rhythmic activity (brain arrhythmias), which affects many brain functions. Neural network rhythms are involved in information processing, storage and retrieval, which are essential for memory consolidation, executive functioning and sensory processing. Therefore, brain arrhythmias could have catastrophic effects on circuit function, underlying the symptoms of various neurological diseases. Moreover, brain arrhythmias can serve as biomarkers for a variety of brain diseases. The aim of this review is to provide evidence linking Aβ and inflammation to neural network dysfunction, focusing on alterations in brain rhythms and their impact on cognition and sensory processing. I reviewed the most common brain arrhythmias characterized in AD, in AD transgenic models and those induced by Aβ. In addition, I reviewed the modulations of brain rhythms in neuroinflammatory diseases and those induced by immunogens, interleukins and microglia. This review reveals that Aβ and inflammation produce a complex set of effects on neural network function, which are related to the induction of brain arrhythmias and hyperexcitability, both closely related to behavioral alterations. Understanding these brain arrhythmias can help to develop therapeutic strategies to halt or prevent these neural network alterations and treat not only the arrhythmias but also the symptoms of AD and other inflammation-related pathologies.

Differential effects of L- and D-lactate on memory encoding and consolidation: Potential role of HCAR1 signaling

The process of memory consolidation is energy-demanding and brain energy deficits result in memory impairments. Indeed, L-lactate, a preferred neuronal energy substrate, enhances the formation of memory, while blockade of the neuronal uptake of L-lactate by either pharmacological means or using its enantiomer D-lactate, impairs memory. Beyond metabolism, both enantiomers of lactate also have signaling properties through the hydroxycarboxylic acid receptor 1 (HCAR1). Thus far, paradigms testing for an effect of lactate on memory modulation have ignored HCAR1 signaling while also mainly performing manipulations before learning and using intracranial administration techniques. Using an inhibitory avoidance (IA) memory protocol, the present study examined the effects of systemic administration of both L- and D-lactate as well as the specific HCAR1 agonist 3,5-dihydroxybenzoic acid (3,5-DHBA) across pre- and post-training periods. We found that post-training subcutaneous injections of either 3,5-DHBA or D-lactate significantly enhanced memory compared to saline controls, whereas L-lactate had no effect, suggesting that HCAR1 signaling in the absence of lactate metabolism supports memory consolidation processes. When administered 15minutes prior to training, D-lactate and 3,5-DHBA impaired memory compared to saline controls. In contrast, L-lactate treated rats showed memory enhancements as compared to D-lactate-treated rats. Taken together, these results suggest different roles for lactate at different memory stages. It is likely that a metabolic role is at play during learning while HCAR1 signaling may play a greater role during consolidation.

Perineuronal nets protect long-term memory by limiting activity-dependent inhibition from parvalbumin interneurons

Perineuronal nets (PNNs), a complex of extracellular matrix molecules that mostly surround GABAergic neurons in various brain regions, play a critical role in synaptic plasticity. The function and cellular mechanisms of PNNs in memory consolidation and reconsolidation processes are still not well understood. We hypothesized that PNNs protect long-term memory by limiting feedback inhibition from parvalbumin (PV) interneurons to projection neurons. Using behavioral, electrophysiological, and optogenetic approaches, we investigated the role of PNNs in fear memory consolidation and reconsolidation and GABAergic long-term potentiation (LTP). We made the discovery that the formation of PNNs was promoted by memory events in the hippocampus (HP), and we also demonstrated that PNN formation in both the HP and the anterior cingulate cortex (ACC) is essential for memory consolidation and reconsolidation of recent and remote memories. Removal of PNNs resulted in evident LTP impairments, which were rescued by acute application of picrotoxin, a GABAA receptor blocker, indicating that enhanced inhibition was the cause of the LTP impairments induced by PNN removal. Moreover, removal of PNNs switched GABAA receptor-mediated long-term depression to LTP through a presynaptic mechanism. Furthermore, the reduced activity of PV interneurons surrounded by PNNs regulated theta oscillations during fear memory consolidation. Finally, optogenetically suppressing PV interneurons rescued the memory impairment caused by removal of PNNs. Altogether, these results unveil the function of PV interneurons surrounding PNNs in protecting recent and remote contextual memory through the regulation of PV neuron GABA release.

A Delayed Advantage: Multi-Session Training at Evening Hours Leads to Better Long-Term Retention of Motor Skill in the Elderly.

The acquisition and retention of motor skills is necessary for everyday functioning in the elderly and may be critical in the context of motor rehabilitation. Recent studies indicate that motor training closely followed by sleep may result in better engagement of procedural (“how to”) memory consolidation processes in the elderly. Nevertheless, elderly individuals are mostly morning oriented and a common practice is to time rehabilitation programs to morning hours. Here, we tested whether the time-of-day wherein training is afforded (morning, 8–10:30 a.m., or evening, 6–9 p.m.) affects the long-term outcome of a multi-session motor practice program (10 sessions across 3–4 weeks) in healthy elderly participants. Twenty-nine (15 women) older adults (60–75 years) practiced an explicitly instructed five-element key-press sequence by repeatedly generating the sequence “as fast and accurately as possible.” The groups did not differ in terms of sleep habits and quality (1-week long actigraphy); all were morning-oriented individuals. All participants gained robustly from the intervention, shortening sequence tapping duration and retaining the gains (> 90%) at 1-month post-intervention, irrespective of the time-of-day of training. However, retesting at 7-months post-intervention showed that the attrition of the training induced gains was more pronounced in the morning trained group compared to the evening group (76 and 56.5% loss in sequence tapping time; 7/14 and 3/14 participants showed a > 5% decline in accuracy relative to end of training, respectively). Altogether, the results show that morning-oriented older adults effectively acquired skill in the performance of a sequence of finger movements, in both morning and evening practice sessions. However, evening training leads to a significant advantage, over morning training, in the long-term retention of the skill. Evening training should be considered an appropriate time window for motor skill learning in older adults, even in individuals with morning chronotype. The results are in line with the notion that motor training preceding a sleep interval may be better consolidated into long-term memory in the elderly, and thus result in lower forgetting rates.

Prior Knowledge Predicts Early Consolidation in Second Language Learning.

Language learning occurs in distinct phases. Whereas some improvement is evident during training, offline memory consolidation processes that take place after the end of training play an important role in learning of linguistic information. The timing of offline consolidation is thought to depend on the type of task, with generalization of implicit knowledge suggested to take more time and sleep to consolidate. The current study aims to investigate individual differences in the timing of consolidation following learning of morphological inflections in a novel language in typical adults. Participants learned to make plural inflections in an artificial language, where inflection was based on morpho-phonological regularities. Participants were trained in the evening, and consolidation was measured after two intervals: 12 h (one night) and 36 h (two nights) post training. We measured both inflection of trained items, which may rely on item-specific learning, and generalization to new untrained items, which requires extraction of morpho-phonological regularities. The results for both trained and un-trained items showed two patterns of consolidation: early versus late, that is while some participants improved during the first night, others, who deteriorated in performance during the first night, improved in the later consolidation interval. Importantly, phonological awareness in L1 predicted early consolidation for trained items. Furthermore, there was no association between participants’ consolidation trajectory in trained and untrained items. Our results suggest that consolidation timing depends on the interaction between task characteristics and individual abilities. Moreover, the results show that prior meta-linguistic knowledge predicts the quality of early consolidation processes. These results are consistent with studies in rodents and humans, showing that prior knowledge accelerates consolidation of newly learnt episodic memory. Finally, the rate of consolidation across exposures to the language might explain some of the variability found in the attained level of second language proficiency.

Accelerated forgetting and verbal memory consolidation process in idiopathic nondement Parkinson’s disease

ObjectiveEpisodic memory impairment and underlying pathophysiology in Parkinson's Disease (PD) is poorly investigated. Formerly, it was thought to be a secondary effect of impairment in fronto-striatal circuit. However, recent studies hypothesized that there is a dual progression of PD and memory loss is possibly related to posterior cortex rather than frontal. To understand the impairment, underlying mechanisms should be investigated. Although consolidation is one of these mechanisms consolidation phase of episodic memory in PD was not investigated yet. Recently accelerated long term forgetting (ALF) phenomenon is emphasized in consolidation researches. MethodHere it is evaluated the presence of accelerated long-term forgetting in nondemented PD as a consequence of a deficit in consolidation process. 32 patients and 33 controls participated in the study. Turkish Verbal Memory Process Test (VMPT) was applied to both groups. Delayed recall (DR) scores collected after 30 min, one week and six weeks. Forgetting rates were calculated based on these scores. Results: There was significant difference in DR scores of patients compared to controls in the 30th minute and sixth week. Forgetting rate between 30th minute-1st week did not differ but 1st-6th week was found statistically significant across groups. Conclusions: To the best of our knowledge, this is the first study investigating verbal memory consolidation in PD. Results suggested that impairment is possibly related to the late phase of consolidation of verbal memory in neocortex.

Long-term verbal memory deficit and associated hippocampal alterations in 22q11.2 deletion syndrome

ABSTRACTChromosome 22q11.2 deletion syndrome (22q11.2DS) is a genetic disease associated with an increased risk for schizophrenia and a specific cognitive profile. In this paper, we challenge the current view of spared verbal memory in 22q11.2DS by investigating verbal memory consolidation processes over an extended time span to further qualify the neuropsychological profile. Our hypotheses are based on brain anomalies of the medial temporal lobes consistently reported in this syndrome.Eighty-four participants (45 with 22q11.2DS), aged 8–24 years old, completed a verbal episodic memory task to investigate long-term memory on four different time delays. We compared trajectories of forgetting between groups (22q11.2DS vs. controls) and analyzed performance inside the 22q11.2DS sample through cluster analyses. Potential links between memory performance and volume of the hippocampal subfields were examined.We showed accelerated long-term forgetting (ALF) in the 22q11.2DS group, visible after a delay of one day. Using mixed models, we showed significant differences in the shape of memory trajectories between subgroups of participants with 22q11.2DS. These sub-groups differed in terms of memory recognition, intellectual functioning, positive psychotic symptoms and grey matter volume of hippocampal subfields but not in terms of age.In conclusion, by investigating memory processes on longer delays than standardized memory tasks, we identified deficits in long-term memory consolidation leading to ALF in 22q11.2DS. Nevertheless, we showed that a subgroup of patients had larger memory consolidation deficit associated with lower intellectual functioning, higher rates of positive psychotic symptoms and hippocampal alterations.

Enhancing Children's Motor Memory Retention Through Acute Intense Exercise: Effects of Different Exercise Durations.

Physical exercise has been proposed as a viable means to stimulate motor learning. Exercise characteristics, including intensity and duration, may play a role in modulating the exercise effect on motor learning. While some evidence exists regarding the benefits of intense and relatively long exercise, little is known about the effect of short exercise bouts on motor learning, especially in children. This study aimed to assess the effect of long versus short intense exercise bouts on the adaptation and consolidation of a rotational visuomotor adaptation task. The participants were 71 healthy children from two sites divided into three groups: long exercise bout (LONG), short exercise bout (SHORT), and no exercise (CON). Children performed a rotated (clockwise 60° rotation) motor task on four different occasions: an adaptation set and 1 h, 24 h, and 7 days delayed retention sets. Exercise bouts were performed prior to the adaptation set. Results showed a group effect during motor adaptation [F(2,68) = 3.160; p = 0.049; = 0.087], but no statistical differences were found between groups. Regarding retention tests, both exercise groups (LONG and SHORT) showed superior retention compared to CON group [F(2,68) = 7.102; p = 0.002; = 0.175]. No differences were found between exercise groups, indicating similar benefits for the two exercise interventions. Overall, whether the exercise duration was long or short, exercise improved motor memory retention as an estimate of memory consolidation process. The use of short exercise bouts may be suitable to improve children’s motor memory consolidation in environments where time constraints exist.

The effects of the attention resource allocation on visual working memory consolidation process

The effects of the attention resource allocation on visual working memory consolidation process

Motor learning induces plastic changes in Purkinje cell dendritic spines in the rat cerebellum

IntroductionThe paramedian lobule of the cerebellum is involved in learning to correctly perform motor skills through practice. Dendritic spines are dynamic structures that regulate excitatory synaptic stimulation. We studied plastic changes occurring in the dendritic spines of Purkinje cells from the paramedian lobule of rats during motor learning. MethodsAdult male rats were trained over a 6-day period using an acrobatic motor learning paradigm; the density and type of dendritic spines were determined every day during the study period using a modified version of the Golgi method. ResultsThe learning curve reflected a considerable decrease in the number of errors made by rats as the training period progressed. We observed more dendritic spines on days 2 and 6, particularly more thin spines on days 1, 3, and 6, fewer mushroom spines on day 3, fewer stubby spines on day 1, and more thick spines on days 4 and 6. ConclusionThe initial stage of motor learning may be associated with fast processing of the underlying synaptic information combined with an apparent “silencing” of memory consolidation processes, based on the regulation of the neuronal excitability.

Schema and Motor-Memory Consolidation

Recent research has demonstrated that memory-consolidation processes can be accelerated if newly learned information is consistent with preexisting knowledge. Until now, investigations of this fast integration of new information into memory have focused on the declarative and perceptual systems. We employed a unique manipulation of a motor-sequence-learning paradigm to examine the effect of experimentally acquired memory on the learning of new motor information. Results demonstrate that new information is rapidly integrated into memory when practice occurs in a framework that is compatible with the previously acquired memory. This framework consists of the ordinal representation of the motor sequence. This enhanced integration cannot be explained by differences in the explicit awareness of the sequence and is observed only if the previously acquired motor memory was consolidated overnight. Results are consistent with the schema model of memory consolidation and offer insights into how previous motor experience can accelerate learning and consolidation processes.

S33. Angiotensin Type 1 Receptor (AT1R) Inhibition Disrupts Reconsolidation of Conditioned Auditory Fear

Recent studies demonstrate that consolidated memories temporarily return to a labile state following retrieval. This window of reconsolidation presents a potential therapeutic target for treatment of psychiatric disorders such as PTSD. The renin-angiotensin system contributes to memory consolidation processes in rodent models of Pavlovian conditioning; however, its role in reconsolidation of auditory fear conditioning has not been investigated.

Correlation of task-related dream content with memory performance of a film task – A pilot study

Dreams could reflect memory consolidation processes during sleep. The present pilot study examined whether the incorporation of a film sequence shows a relationship to task performance. Twenty-two participants (17 women, 5 men) were exposed to a late-night paradigm in which they were shown a film sequence prior to the second sleep-onset. REM dreams and morning dreams have been collected. Compared with those of a control group the incorporation of film elements in the study group dreams was only higher for morning dream reports on one of two scales. The incorporation rate in morning dreams correlated on one scale with increased memory task performance. Due to the consolidation of declarative tasks, mainly during NREM, and procedural tasks during REM sleep, dream reports should be collected in the respective sleep stage in which the learning task is consolidated. Furthermore, tasks with high incorporation rates should be selected to show the relationship to task performance consistently.

Mephedrone Impact on Matrix Metalloproteinases Activity - Do they Influence the Memory Processes?

The use of drugs of addiction, as mephedrone, is associated with functional neuronal disorders due to remodeling of the nervous tissue. Key enzymes in remodeling are extracellular matrix (ECM) proteases like matrix metalloproteases (MMPs). Recently, MMPs have been of great interest as some studies point to a fact that the alterations in structural remodeling of synaptic connections modify learning-dependent changes, which remain active even after a prolonged period of abstinence. This entails a continuous development of dependence. The aim of the study was to determine the influence of subchronic exposure to three different doses of mephedrone on the activity of MMP-2 and 9 in hippocampus and prefrontal cortex and how this was correlated with memory processes in mice. The homogenates of hippocampus and cortex were assayed for MMP-2 and MMP-9 activity by gelatin zymography. Memory consolidation processes were evaluated in the passive avoidance (PA) test. The study confirmed the dose-dependent increase in activity of MMP-2 and -9 exerted by subchronic administration of mephedrone. Moreover, the highest dose of mephedrone attenuated consolidation of memory and learning processes. We could hypothesize that inhibition of MMPs can be considered as a therapeutic option for the treatment of addictive behaviors associated with cognitive processes. Moreover, further studies are required to find out if elevated activities of MMPs contribute to brain damage or recovery from brain damage caused directly by mephedrone.

The Disruption of Memory Consolidation of Duration Introduces Noise While Lengthening the Long-Term Memory Representation of Time in Humans.

This study examined the effect of an interference task on the consolidation of duration in long-term memory. In a temporal generalization task, the participants performed a learning phase with a reference duration that either was, or was not, followed 30 min later by a 15-min interference task. They were then given a memory test, 24 h later. Using different participant groups, several reference durations were examined, from several hundred milliseconds (600 ms) to several seconds (2.5, 4, and 8 s). The results showed that the scalar timing property (i.e., precision proportional to judged duration) was preserved despite the interference task given during the memory consolidation process. However, the interference task increased the variability of time judgment and tended to produce a lengthening effect in all reference duration conditions. The modeling of individual data with parameters derived from scalar expectancy theory suggests that disrupting the memory consolidation of learned reference durations introduces noise in their representation in memory, with time being specifically distorted toward a lengthened duration.

Fear memory-induced alterations in the mRNA expression of G proteins in the mouse brain and the impact of immediate posttraining treatment with morphine

Disturbances in fear-evoked signal transduction in the hippocampus (HP), the nuclei of the amygdala (AMY), and the prefrontal cortex (PFC) underlie anxiety-related disorders. However, the molecular mechanisms underlying these effects remain elusive. Heterotrimeric G proteins (GPs) are divided into the following four families based on the intracellular activity of their alpha subunit (Gα): Gα(s) proteins stimulate cyclic AMP (cAMP) generation, Gα(i/o) proteins inhibit the cAMP pathway, Gα(q/11) proteins increase the intracellular Ca++ concentration and the inositol trisphosphate level, and Gα(12/13) proteins activate monomeric GP-Rho. In the present study, we assessed the effects of a fear memory procedure on the mRNA expression of the Gα subunits of all four GP families in the HP, AMY and PFC. C57BL/6 J mice were subjected to a fear conditioning (FC) procedure followed by a contextual or cued fear memory test (CTX-R and CS-R, respectively). Morphine (MOR, 1 mg/kg/ip) was injected immediately after FC to prevent the fear consolidation process. Real-time quantitative PCR was used to measure the mRNA expression levels of Gα subunits at 1 h after FC, 24 h after FC, and 1 h after the CTX-R or CS-R. In the HP, the mRNA levels of Gα(s), Gα(12) and Gα(11) were higher at 1 h after training. Gα(s) levels were slightly lower when consolidation was stabilized and after the CS-R. The mRNA levels of Gα(12) were increased at 1 h after FC, returned to control levels at 24 h after FC and increased again with the CTX-R. The increase in the Gα(11) level persisted at 24 h after FC and after CTX-R. In the AMY, no specific changes were induced by FC. In the PFC, CTX-R was accompanied by a decrease in Gα(i/o) mRNA levels; however, only Gα(i2) downregulation was prevented by MOR treatment. Hence, the FC-evoked changes in Gα mRNA expression were observed mainly in the HP and connected primarily to contextual learning. These results suggest that the activation of signaling pathways by Gα(s) and Gα(12) is required to begin the fear memory consolidation process in the HP, while signal transduction via Gα(11) is implicated in the maintenance of fear consolidation. In the PFC, the downregulation of Gα(i2) appears to be related to the contextual learning of fear.

Mapping the Neural Substrates of Recent and Remote Visual Imprinting Memory in the Chick Brain.

Social attachment formed by filial imprinting in newborn chicks undergoes a process of memory consolidation that involves rearrangement of its neural storage substrates. In the first 3 h after imprinting it depends on the integrity of the intermediate medial mesopallium (IMM) and beyond that time on unidentified memory storage structures dubbed S’. To search for the S’ memory system in the chick brain, we mapped and compared patterns of activity induced by retrieval of filial attachment memory before and after this critical transition. Chicks were trained in the visual imprinting task, and their memory was reactivated by imprinting stimulus either 1 h (recent memory retrieval) or 24 h (remote memory retrieval) after the completion of training. Patterns of brain activity were mapped by in situ hybridization to mRNA of an immediate early gene c-fos. We also mapped c-fos expression induced by the first presentation of the imprinting stimulus. Memory retrieval triggered massive c-fos expression in the chick brain both 1 and 24 h after the end of training. These activity patterns mostly coincided with the c-fos expression induced by the first presentation of imprinting stimulus. However, in the hippocampus c-fos induction was observed only after the first exposure to imprinting stimulus but not after memory retrieval. In the IMM, medio-rostral nidopallium/mesopallium, and hyperpallium densocellulare c-fos activation was induced by retrieval of only the remote but not of the recent memory. These c-fos mapping data point to the candidate brain structures for systems reorganization of imprinting memory in chicks.

Guilty by association: Time-dependent memory consolidation facilitates the generalization of negative – but not positive – person memories to group and self-judgments

Over time, memory changes. Memory consolidation processes suggest that time produces qualitative changes in social memory rather than just quantitative changes in the amount of memories retrieved. As newly learned information becomes integrated into long-term memory, it is used in a more generalized fashion. Further, memory for negative (versus neutral or positive) information is bolstered over time. The present studies tested the hypotheses that over time, negative, but not positive, group information would generalize to other group members (Experiment 1) and to the self (Experiment 2). In Experiment 1, participants learned personal information about two members of two groups. Two members of one group were associated with negative trait information, while two members of the other group were associated with positive trait information. Participants then made trait and evaluative judgments about members of both groups. In Experiment 2, participants learned positive and negative information about their ingroup and an outgroup. Participants then evaluated themselves on those traits. Results were consistent with hypotheses. Participants generalized negative traits to members of the same group and generalized negative ingroup traits to evaluations of themselves, but only at a long-delay test.

Glucocorticoid response to stress induction prior to learning is negatively related to subsequent motor memory consolidation.

Hippocampal activity during early motor sequence learning is critical to trigger subsequent sleep-related consolidation processes. Based on previous evidence that stress-induced cortisol release modulates hippocampal activity, the current study investigates whether exposure to stress prior to motor sequence learning influences the ensuing learning and overnight consolidation process. Seventy-four healthy young adults were exposed to a stressor (i.e., the socially evaluated cold pressor test, SECPT) or a control procedure before initial training on a bimanual motor sequence learning task. Participants were retested on the motor task 24 h (including a night of sleep) after training to assess memory consolidation. Our results indicate that the SECPT, as compared to the control condition, induced significant physiological stress responses as evidenced by increased heart rate and blood pressure as well as elevated salivary cortisol concentrations. Cortisol concentration in the stress group reached peak levels immediately before and stayed significantly elevated for the full duration of initial motor learning before returning to baseline during the consolidation period. Stress induction prior to learning did not, on average, influence initial performance nor subsequent motor memory consolidation as indicated by similar overnight gains in performance in both groups. However, higher levels of stress-induced cortisol prior to training were correlated to smaller overnight gains in performance speed. These results indicate that the glucocorticoid response to a stressful encounter experienced prior to hippocampal-mediated motor learning is negatively related to subsequent memory consolidation processes.

Dreaming during REM sleep: autobiographically meaningful or a simple reflection of a Hebbian-based memory consolidation process?

REM sleep is a state of desynchronized electrophysiological activity of the brain. It is usually accompanied by mental activity characterized by a succession of complex visual experiences commonly referred to as dreaming. Although REM sleep and dreaming are not implicitly conjoined, when they co-occur, they have a very distinct phenomenology, as, typically, the dream plot is bizarre and incohesive which is mirrored in heightened brain activation coupled with strongly attenuated coherence levels. At the same time, owing to increased limbic system activity, REM sleep dreams are highly emotional. Moreover, concrete emotions are often unrelated to dream events. Nevertheless, REM sleep dreams are often subjectively perceived as story-like and autobiographically meaningful. Indeed, elements of salient life events, attachment figures, and personally relevant emotions, especially trauma, seem to have a higher probability of re-appearing in dreams, albeit the dream plot itself remains highly distorted. This has prompted several theories on the interpretability of dreams, some authors leaning towards dreams reflecting waking mentation, others suggesting complete dissociation between waking and dreaming, both sides not fully accounting for empirical findings. In this review, we provide an overview of recent findings on the factors mediating REM sleep neurophysiology and dream content. As a first step towards integration of conflicting research results, we introduce a testable model (Trace-Spur-model) based on Hebbian theory of neural networks, proposing that dream bizarreness is a function of state-related modulations in synaptic strength allowing for hyper-associative mental activity, possibly enabling either a restructuring and integrative consolidation or extinction of learning experiences acquired in waking. In this model, dreams are viewed as phenomenological expressions of this neurophysiologic activity where dream recall allows a fragmentary witnessing of such processes, similar to peeking into an enduring and complex networking system. However, the content of the recollected dream is probably strongly deterred by autobiographical memory bias, favoring those images we can form some sort of association with.