Learned helplessness in the cockroach (Periplaneta americana)

For 3 consecutive days cockroaches (Periplaneta americana) were exposed to either escapable, inescapable, or no shock in an escape task. Twenty-four hours later they were tested in a shuttlebox escape task. There were reliable differences between escapable and inescapable animals and between inescapable and control animals in both escape latencies and the number of failures to escape.     

Immunization against learned helplessness in the cockroach (Periplaneta americana)

Cockroaches exposed to one day of escapable shock prior to three days of inescapable shock did not become helpless on a shuttlebox-escape task. Like dogs and rats, cockroaches are immunized against learned helplessness by prior experience with escapable shock.     

Forced exercise blocks learned helplessness in the cockroach (Periplaneta americana)

For three consecutive days, two groups of adult female cockroaches (Periplaneta americana) (ns = 10) received inescapable shock. 24 hr. later one group was exposed to 10 min. of forced exercise on a treadmill while the other group received no exercise. Both groups were then run in a shuttlebox escape task. The cockroaches exposed to forced exercise did not become helpless in the shuttlebox escape task.     

Memory reactivation and consolidation during sleep

Do our memories remain static during sleep, or do they change? We argue here that memory change is not only a natural result of sleep cognition, but further, that such change constitutes a fundamental characteristic of declarative memories. In general, declarative memories change due to retrieval events at various times after initial learning and due to the formation and elaboration of associations with other memories, including memories formed after the initial learning episode. We propose that declarative memories change both during waking and during sleep, and that such change contributes to enhancing binding of the distinct representational components of some memories, and thus to a gradual process of cross-cortical consolidation. As a result of this special form of consolidation, declarative memories can become more cohesive and also more thoroughly integrated with other stored information. Further benefits of this memory reprocessing can include developing complex networks of interrelated memories, aligning memories with long-term strategies and goals, and generating insights based on novel combinations of memory fragments. A variety of research findings are consistent with the hypothesis that cross-cortical consolidation can progress during sleep, although further support is needed, and we suggest some potentially fruitful research directions. Determining how processing during sleep can facilitate memory storage will be an exciting focus of research in the coming years.The idea that memory storage is supported by events that take place in the brain while a person is sleeping is an idea that is only rarely acknowledged in the neuroscience community. At present, most memory research proceeds with no mention of any influence of sleep on memory. Nonetheless, this hypothesis is gaining empirical support. Research into connections between memory and sleep represents a burgeoning enterprise at the crossroads of traditional memory research and sleep research, an enterprise poised to provide novel insights into the human experience.This article presents some speculations about connections between memory and sleep. We entertain the notion that declarative memories are subject to modification during sleep, and that enduring storage of such memories is systematically influenced by neural events taking place during sleep. Although other types of memory may also be subject to change during sleep (see Maquet et al. 2003), we emphasize declarative memory here.This article also functions as an introduction to the set of papers selected for this special issue of Learning & Memory. These papers together outline portions of the current empirical basis for memory-sleep connections, including research in humans and in nonhuman animals. The findings are tantalizing, and yet there are undoubtedly major gaps in our knowledge about the functions of sleep and about how sleep may be related to memory storage. Future research on this topic is bound to grow in exciting and unpredictable ways. Here, we explore questions about declarative memory and sleep that may serve as a useful guide for such research.     

Memory consolidation and contextual interference effects with computer games

Some investigators of the contextual interference effect contend that there is a direct relation between the amount of practice and the contextual interference effect based on the prediction that the improvement in learning tasks in a random practice schedule, compared to a blocked practice schedule, increases in magnitude as the amount of practice during acquisition on the tasks increases. Research using computer games in contextual interference studies has yielded a large effect (f = .50) with a random practice schedule advantage during transfer. These investigations had a total of 36 and 72 acquisition trials, respectively. The present study tested this prediction by having 72 college students, who were randomly assigned to a blocked or random practice schedule, practice 102 trials of three computer-game tasks across three days. After a 24-hr. interval, 6 retention and 5 transfer trials were performed. Dependent variables were time to complete an event in seconds and number of errors. No significant differences were found for retention and transfer. These results are discussed in terms of how the amount of practice, task-related factors, and memory consolidation mediate the contextual interference effect.     

Memory consolidation effects on memory stabilization and item integration in older adults

This study examined the differential effects of aging on consolidation processes that strengthen newly acquired memory traces in veridical form (memory stabilization) versus consolidation processes that are responsible for integrating these memory traces into an existing body of knowledge (item integration). Older adults learned 13 nonwords and were tested on their memory for the nonwords, and on whether these nonwords impacted upon processing of similar-sounding English words immediately and 24 hours later. Participants accurately recognized the nonwords immediately, but showed significant decreases in delayed recognition and recall. In comparison, the nonwords impacted upon processing of similar-sounding words only in the delayed test. Together, these findings suggest that memory consolidation processes may be more evident in item integration than memory stabilization processes for new declarative memories in older adults.     

Memory consolidation during sleep: interactive effects of sleep stages and HPA regulation

Sleep is critically involved in the consolidation of previously acquired memory traces. However, nocturnal sleep is not uniform but is subject to distinct changes in electrophysiological and neuroendocrine activity. Specifically, the first half of the night is dominated by slow wave sleep (SWS), whereas rapid eye movement (REM) sleep prevails in the second half. Concomitantly, hypothalamo-pituitary-adrenal (HPA) activity as indicated by cortisol release is suppressed to a minimum during early sleep, while drastically increasing during late sleep. We have shown that the different sleep stages and the concomitant glucocorticoid release are interactively involved in the consolidation of different types of memories. SWS-rich early sleep has been demonstrated to benefit mainly the consolidation of hippocampus-dependent declarative memories (i.e. facts and episodes). In contrast, REM sleep-rich late sleep was shown to improve in particular emotional memories involving amygdalar function, as well as procedural memories (for skills) not depending on hippocampal or amygdalar function. Enhancing plasma glucocorticoid concentrations during SWS-rich early sleep counteracted hippocampus-dependent declarative memory consolidation, but did not affect hippocampus-independent procedural memory. Preventing the increase in cortisol during late REM sleep-rich sleep by administration of metyrapone impaired hippocampus-dependent declarative memory but enhanced amygdala-dependent emotional aspects of memory. The data underscore the importance of pituitary-adrenal inhibition during early SWS-rich sleep for efficient consolidation of declarative memory. The increase in cortisol release during late REM sleep-rich sleep may counteract an overshooting consolidation of emotional memories.     

Memory consolidation in both trace and delay fear conditioning is disrupted by intra-amygdala infusion of the protein synthesis inhibitor anisomycin

Memory for delay fear conditioning requires the synthesis of new mRNA and protein in the basolateral amygdala. It is currently unknown whether similar molecular processes in the amygdala are required for the formation of trace fear memory, in which a stimulus-free interval is inserted between the conditional stimulus (CS) and unconditional stimulus (UCS). Here, we show that infusion of the protein synthesis inhibitor anisomycin into the basolateral amygdala disrupts consolidation of both trace and delay fear conditioning. This is the first evidence that protein synthesis in the amygdala is necessary for the formation of both trace and delay fear memory.     

Time-course of 5-HT6 receptor mRNA expression during memory consolidation and amnesia

Growing evidence indicates that antagonists of the 5-hydroxytryptamine (serotonin) receptor₆ (5-HT₆) improve memory and reverse amnesia although the mechanisms involved are poorly understood. Hence, in this paper RT-PCR was used to evaluate changes in mRNA expression of 5-HT₆ receptor in trained and untrained rats treated with the 5-HT₆ receptor antagonist SB-399885 and amnesic drugs scopolamine or dizocilpine. Changes in mRNA expression of 5-HT₆ receptor were investigated at different times in prefrontal cortex, hippocampus and striatum. Data indicated that memory in the Pavlovian/instrumental autoshaping task was a progressive process associated to reduced mRNA expression of 5-HT₆ receptor in the three structures examined. SB-399885 improved long-term memory at 48 h, while the muscarinic receptor antagonist scopolamine or the non-competitive NMDA receptor antagonist dizocilpine impaired it at 24 h. Autoshaping training and treatment with SB-399885 increased 5-HT₆ receptor mRNA expression in (maximum increase) prefrontal cortex and striatum, 24 or 48 h. The scopolamine-induced amnesia suppressed 5-HT₆ receptor mRNA expression while the dizocilpine-induced amnesia did not modify 5-HT₆ receptor mRNA expression. SB-399885 and scopolamine or dizocilpine were able to reestablish memory and 5-HT₆ receptor mRNA expression. These data confirmed previous memory evidence and of more interest is the observation that training, SB-399885 and amnesic drugs modulated 5-HT₆ receptor mRNA expression in prefrontal cortex, hippocampus and striatum. Further investigation in different memory tasks, times and amnesia models together with more complex control groups might provide further clues.     

Memory consolidation for the discrimination of frequency-modulated tones in mongolian gerbils is sensitive to protein-synthesis inhibitors applied to the auditory cortex

Differential conditioning of Mongolian gerbils to linearly frequency-modulated tones (FM) has recently received experimental attention. In the study of the role of cerebral protein synthesis for FM discrimination memory, gerbils received post-training bilateral injections of anisomycin into the auditory cortex under light halothane anesthesia. Compared with saline-treated controls, anisomycin-treated gerbils showed a discrimination decrement during the subsequent three days of training. They markedly improved their performance within training sessions, but started each session at low levels. When repeatedly trained gerbils received post-session injections of anisomycin, discrimination performance during subsequent sessions was similar to the pre-injection performance, indicating that retention, retrieval, reconsolidation, and expression of the established reaction were not affected. However, the improvement of a partially established discrimination reaction was impaired after this treatment. Intracortical injections of emetine confirmed this finding. Neither drug affected FM discrimination learning when given several days before the initial training. Our results suggest that protein-synthesis inhibitors applied to the auditory cortex of gerbils during the post-acquisition phase interfered with learning and memory-related aspects of FM processing. The resulting deficit was evident for a number of post-injection training days. This effect was probably due to impaired consolidation, i.e., processes required for long-term stabilization or retrieval of the memory trace while leaving short-term memory intact.     

Atypicalities in sleep and semantic consolidation in autism

Sleep is known to support the neocortical consolidation of declarative memory, including the acquisition of new language. Autism spectrum disorder (ASD) is often characterized by both sleep and language learning difficulties, but few studies have explored a potential connection between the two. Here, 54 children with and without ASD (matched on age, nonverbal ability and vocabulary) were taught nine rare animal names (e.g., pipa). Memory was assessed via definitions, naming and speeded semantic decision tasks immediately after learning (pre‐sleep), the next day (post‐sleep, with a night of polysomnography between pre‐ and post‐sleep tests) and roughly 1 month later (follow‐up). Both groups showed comparable performance at pre‐test and similar levels of overnight change on all tasks; but at follow‐up children with ASD showed significantly greater forgetting of the unique features of the new animals (e.g., pipa is a flat frog). Children with ASD had significantly lower central non‐rapid eye movement (NREM) sigma power. Associations between spindle properties and overnight changes in speeded semantic decisions differed by group. For the TD group, spindle duration predicted overnight changes in responses to novel animals but not familiar animals, reinforcing a role for sleep in the stabilization of new semantic knowledge. For the ASD group, sigma power and spindle duration were associated with improvements in responses to novel and particularly familiar animals, perhaps reflecting more general sleep‐associated improvements in task performance. Plausibly, microstructural sleep atypicalities in children with ASD and differences in how information is prioritized for consolidation may lead to cumulative consolidation difficulties, compromising the quality of newly formed semantic representations in long‐term memory.     

Behavioral interference and C/EBPbeta expression in the insular-cortex reveal a prolonged time period for taste memory consolidation

Memory consolidation is defined as the time window during which the memory trace is susceptible to behavioral, electrical, or pharmacological interventions. Here, we presented rats with two novel tastes at consecutive time intervals. Clear interference was evident when a novel taste formed the second taste input whereby, surprisingly, the time window for interference was found to last more than 10 h. In addition, we detected an increase of C/EBPbeta protein expression in the gustatory cortex 18 h after novel taste learning. This modulation was attenuated by a subsequent novel taste. Our findings reveal temporal constraints and a lingering nature of taste memory consolidation.     

Value conflict and post-decision consolidation

The primary goal of the present study was to investigate how the mental representations of value conflicts are restructured after a decision. A value conflict exists if a chosen alternative is less attractive than a non-chosen alternative on one important attribute when a decision is made. In order to follow up earlier field studies with no experimental control over value conflicts, the present study induced value conflicts in the laboratory. This was done through associating the more attractive of two alternatives with a smaller probability of success. The first hypothesis was that consolidation of value conflict attributes should follow the same pattern when the conflict is controlled experimentally as in earlier studies of real-life decisions. The second hypothesis was that consolidation should be weaker in a non-consequential laboratory study than in the earlier real-life studies. The third hypothesis was that stronger value conflicts (that is, value conflict on more important attributes) lead to greater consolidation effects than weaker value conflicts. The results showed that participants consolidated the value conflicts in the same way as in real-life decisions with the difference that also less important attributes were consolidated in the present study. However, the consolidation effects were not so strong that they caused advantage reversals on a conflict attribute, as in the earlier field studies with real outcomes and consequences. There was no relationship between strength of conflict and consolidation. The fact that no advantage reversals were registered leads to questions about the ecological validity of laboratory studies of non-consequential decision making.     

Hippocampal gene expression profiling in spatial discrimination learning

Learning and long-term memory are thought to involve temporally defined changes in gene expression that lead to the strengthening of synaptic connections in selected brain regions. We used cDNA microarrays to study hippocampal gene expression in animals trained in a spatial discrimination-learning paradigm. Our analysis identified 19 genes that showed statistically significant changes in expression when comparing Nai;ve versus Trained animals. We confirmed the changes in expression for the genes encoding the nuclear protein prothymosin(alpha) and the delta-1 opioid receptor (DOR1) by Northern blotting or in situ hybridization. In additional studies, laser-capture microdissection (LCM) allowed us to obtain enriched neuronal populations from the dentate gyrus, CA1, and CA3 subregions of the hippocampus from Nai;ve, Pseudotrained, and spatially Trained animals. Real-time PCR examined the spatial learning specificity of hippocampal modulation of the genes encoding protein kinase B (PKB, also known as Akt), protein kinase C(delta) (PKC(delta)), cell adhesion kinase(beta) (CAK(beta), also known as Pyk2), and receptor protein tyrosine phosphatase(zeta/beta) (RPTP(zeta/beta)). These studies showed subregion specificity of spatial learning-induced changes in gene expression within the hippocampus, a feature that was particular to each gene studied. We suggest that statistically valid gene expression profiles generated with cDNA microarrays may provide important insights as to the cellular and molecular events subserving learning and memory processes in the brain.     

Glucocorticoid release and memory consolidation in men and women

Glucocorticoid hormones have been shown to enhance memory consolidation when applied at low doses posttraining, but are ineffective or impair memory at high doses. In a test of whether this quadratic relationship also exists for endogenously released glucocorticoids, healthy men and women received cold-pressor stress (CPS) or a control procedure immediately after reading a relatively neutral story and were tested for retention 1 week later. Cortisol levels in response to the stressor were assayed from saliva. CPS significantly elevated salivary cortisol in both sexes, but enhanced memory only in male subjects. Among CPS-treated male subjects, there was a significant quadratic correlation between cortisol release posttraining and subsequent memory. Thus, these findings represent the first demonstration of an inverted-U relationship between activity of endogenous stress hormones and human memory.     

Memory and aging in context

Much research has indicated that aging is accompanied by decrements in memory performance across a wide variety of tasks and situations. A dominant perspective is that these age differences reflect normative changes in the integrity and efficiency of the information-processing system. Contextual perspectives of development, however, argue for consideration of a broader constellation of factors as determinants of both intraindividual change and interindividual variation in memory functioning. The validity of the contextual perspective in characterizing the relationship between aging and memory is examined through a review of studies exploring a variety of alternative mechanisms associated with age differences in performance. It is concluded that a more multidimensional approach to the study of aging and memory is warranted.     

工作记忆与情景记忆的相互作用

虽然Baddeley的工作记忆模型得到大量实验研究的支持,但是有关工作记忆和长时记忆之间的关系未能得到详细阐述。来自神经心理学的证据表明,工作记忆与情景长时记忆任务均诱发了前额区的激活,但同时发现前额区存在不同的功能分区,可能在工作记忆与情景记忆过程中具有独立的执行功能。工作记忆与情景记忆的相互作用是当前记忆研究关注的问题。已有研究发现,在情景记忆对工作记忆的作用过程中,时间进程与头皮分布均显示了年龄效应与材料加工特点。而工作记忆对情景记忆的作用中,则发现工作记忆早期加工可能对情景记忆的成功形成有更大促进作用。今后的研究应在理论模型支持下,利用多种技术手段探讨两种记忆相互作用的神经加工机制