Patterns of brain-electrical activity during declarative memory performance in 10-month-old infants

This study of infant declarative memory concurrently examined brain-electrical activity and deferred imitation performance in 10-month-old infants. Continuous electroencephalogram (EEG) measures were collected throughout the activity-matched baseline, encoding (modeling) and retrieval (delayed test) phases of a within-subjects deferred imitation task. Infants were divided into two memory performance groups based on the exhibition of ordered-recall after a 24-h delay. Whereas no group differences were found in EEG collected during encoding, performance-group differences in EEG were present during retrieval. Infants who successfully displayed ordered-recall showed a pattern of increasing EEG from baseline to task at anterior temporal scalp locations, whereas infants showing no ordered-recall displayed no changes in EEG from baseline to task. These findings are discussed with respect to the biobehavioral developments underlying declarative memory abilities.     

Patterns of brain-electrical activity during declarative memory performance in 10-month-old infants

This study of infant declarative memory concurrently examined brain-electrical activity and deferred imitation performance in 10-month-old infants. Continuous electroencephalogram (EEG) measures were collected throughout the activity-matched baseline, encoding (modeling) and retrieval (delayed test) phases of a within-subjects deferred imitation task. Infants were divided into two memory performance groups based on the exhibition of ordered-recall after a 24-h delay. Whereas no group differences were found in EEG collected during encoding, performance-group differences in EEG were present during retrieval. Infants who successfully displayed ordered-recall showed a pattern of increasing EEG from baseline to task at anterior temporal scalp locations, whereas infants showing no ordered-recall displayed no changes in EEG from baseline to task. These findings are discussed with respect to the biobehavioral developments underlying declarative memory abilities.     

Cannabinoid and cholinergic systems interact during performance of a short-term memory task in the rat

It is now well established that cannabinoid agonists such as Δ⁹–tetrahydrocannabinol (THC), anandamide, and WIN 55,212-2 (WIN-2) produce potent and specific deficits in working memory (WM)/short-term memory (STM) tasks in rodents. Although mediated through activation of CB1 receptors located in memory-related brain regions such as the hippocampus and prefrontal cortex, these may, in part, be due to a reduction in acetylcholine release (i.e., cholinergic hypofunction). To determine the interaction between cannabinoid and cholinergic systems, we exposed rats treated with WIN-2 or cholinergic drugs to a hippocampal-dependent delayed nonmatch to sample (DNMS) task to study STM, and recorded hippocampal single-unit activity in vivo. WIN-2 induced significant deficits in DNMS performance and reduced the average firing and bursting rates of hippocampal principal cells through a CB1 receptor-mediated mechanism. Rivastigmine, an acetylcholinesterase inhibitor, reversed these STM deficits and normalized hippocampal discharge rates. Effects were specific to 1 mg/kg WIN-2 as rivastigmine failed to reverse the behavioral and physiological deficits that were observed in the presence of MK-801, an NMDA receptor antagonist. This supports the notion that cannabinoid-modulated cholinergic activity is a mechanism underlying the performance deficits in DNMS. Whether deficits are due to reduced nicotinic or muscarinic receptor activation, or both, awaits further analysis.Administration of both synthetic and phytocannabinoids, including Δ⁹–tetrahydrocannabinol (Δ⁹–THC), WIN 55,212-2 (WIN-2), and CP 55,940, impair working memory (WM) and short-term memory (STM) through a CB1 receptor-mediated mechanism in rats (Lichtman et al. 1995; Lichtman and Martin 1996; Hampson and Deadwyler 1998, 1999, 2000; Braida and Sala 2000; Egashira et al. 2002). This suggestive evidence for endocannabinoid involvement in memory formation was confirmed by Terranova and coworkers (1996), who demonstrated that the CB1 receptor antagonist rimonabant facilitated short-term olfactory memory, and this was partially reversed by the muscarinic receptor antagonist scopolamine. This suggests an interaction between cannabinoid and cholinergic systems such that endocannabinoid tone suppresses cholinergic transmission. Consequently, rats pretreated with eptastigmine, a second-generation cholinesterase inhibitor remained unaffected by the full CB1 receptor agonist CP 55,940 when tested in an eight arm radial maze (Braida and Sala 2000). And more recent evidence from Mishima and coworkers (2002) suggests that a block of cholinesterase with physostigmine and tetrahydroaminoacridine protects against WM impairments induced by Δ⁹–THC. These findings further support a potential role of the cholinergic system in cannabinoid-induced memory impairments.The exact mechanisms for this interaction still remain elusive, although cholinergic projection neurons from medial septum to hippocampus are likely to play an important role (Harkany et al. 2003, 2005; Fitz et al. 2008). However, the neuromodulatory action of pharmacologically active cannabinoids on septo-hippocampal cholinergic activity in vivo remains unexplored. Within the hippocampus, cannabinoids presynaptically inhibit the release of acetylcholine, possibly through the activation of CB1 receptors located on cholinergic nerve terminals given that these effects were blocked by rimonabant (Gifford and Ashby Jr. 1996; Gifford et al. 1997a, 2000; Kathmann et al. 2001a). Direct in vivo microdialysis studies in awake rats also showed cannabinoid-induced decreases in acetylcholine release in the hippocampus through a CB1 receptor-mediated mechanism (Gessa et al. 1997; Carta et al. 1998). High doses of rimonabant alone increase the amount of acetylcholine release in the hippocampus (Gessa et al. 1997, 1998) either by blocking the tonic inhibitory influence of endocannabinoids and/or through its inverse agonism at CB1 receptors. Such actions are in agreement with a 100% greater increase in electrically evoked hippocampal acetylcholine release in CB1^−/− mice (Kathmann et al. 2001b).In contrast, low doses of Δ⁹–THC (0.01–0.15 mg/kg), WIN-2 (0.01–0.5 mg/kg), and HU-210 (0.001–0.004 mg/kg) have been shown to enhance acetylcholine release (Acquas et al. 2000, 2001), indicating that cannabinoid modulation of acetylcholine release in the hippocampus is “biphasic.” This has been further supported by the work carried out by Tzavara and coworkers (2003), who demonstrated that low (0.5 mg/kg, intraperitoneally [i.p.]) and high (5 mg/kg, i.p.) doses of WIN-2 induce transient stimulation and prolonged inhibition of hippocampal acetylcholine efflux, respectively. This demonstrates that the dose of cannabinoids plays a key role in determining how much acetylcholine is released in the hippocampus.Such an interaction is likely to play an important role during the performance of a delayed nonmatch to sample (DNMS) task but has not been explored. Hence, a comprehensive pharmacological assessment was carried out here to (1) reveal the existence of such an interaction in terms of DNMS performance and (2) assess a possible cannabinoid-acetylcholine cross-talk on burst characteristics of hippocampal principal cells in CA3 and CA1.     

奖赏与自我加工对记忆的影响

【摘 要】目的:从外显和内隐层面探讨奖赏与自我加工对记忆的影响。方法：以大学生为被试,以人格形容词为实验材料,采用R/K范式,测量被试对识记词语的记忆效果。结果：（1）外显记忆层面,奖赏与自我加工均促进了记忆效果;（2）在内隐记忆层面,自我存在记忆的加工优势,但是没有发现奖赏加工对记忆的影响。结论：自我相关刺激促进了内隐和外显记忆的加工,奖赏刺激只对外显记忆有影响,实验结果支持独立平行模型,即在不同记忆层面,奖赏加工与自我参照加工存在不同加工机制。     

Effects of emotion and age on performance during a think/no-think memory task

Recent studies have demonstrated that young adults can voluntarily suppress information from memory when directed to. After learning novel word pairings to criterion, participants are shown individual words and instructed either to "think" about the associated word, or to put it out of mind entirely ("no-think"). When given a surprise cued recall test, participants typically show impaired recall for no-think words relative to think or "control" (un-manipulated) words. The present study investigated whether this controlled suppression effect persists in an aged population, and examined how the emotionality of the to-be-suppressed word affects suppression ability. Data from four experiments using the think/no-think task demonstrate that older and younger adults can suppress information when directed to (Experiment 1), and the age groups do not differ significantly in this ability. Experiments 2 through 4 demonstrate that both age groups can suppress words that are emotional (positive or negative valence) or neutral. The suppression effect also persists even if participants are tested using independent probe words that are semantically related to the target words but were not the studied cue words (Experiments 3 and 4). These data suggest that the cognitive functioning necessary to suppress information from memory is present in older adulthood, and that both emotional and neutral information can be successfully suppressed from memory.     

Reconsolidation of declarative memory in humans

The reconsolidation hypothesis states that a consolidated memory could again become unstable and susceptible to facilitation or impairment for a discrete period of time after a reminder presentation. The phenomenon has been demonstrated in very diverse species and types of memory, including the human procedural memory of a motor skill task but not the human declarative one. Here we provide evidence for both consolidation and reconsolidation in a paired-associate learning (i.e., learning an association between a cue syllable and the respective response syllable). Subjects were given two training sessions with a 24-h interval on distinct verbal material, and afterward, they received at testing two successive retrievals corresponding to the first and second learning, respectively. Two main results are noted. First, the first acquired memory was impaired when a reminder was presented 5 min before the second training (reconsolidation), and also when the second training was given 5 min instead of 24 h after the first one (consolidation). Second, the first retrieval proved to influence negatively on the later one (the retrieval-induced forgetting [RIF] effect), and we used the absence of this RIF effect as a very indicator of the target memory impairment. We consider the demonstration of reconsolidation in human declarative memory as backing the universality of this phenomenon and having potential clinical relevance. On the other hand, we discuss the possibility of using the human declarative memory as a model to address several key topics of the reconsolidation hypothesis.     

Sleep in children improves memory performance on declarative but not procedural tasks

Sleep supports the consolidation of memory in adults. Childhood is a period hallmarked by huge demands of brain plasticity as well as great amounts of efficient sleep. Whether sleep supports memory consolidation in children as in adults is unclear. We compared effects of nocturnal sleep (versus daytime wakefulness) on consolidation of declarative (word-pair associates, two-dimensional [2D] object location), and procedural memories (finger sequence tapping) in 15 children (6-8 yr) and 15 adults. Beneficial effects of sleep on retention of declarative memories were comparable in children and adults. However, opposite to adults, children showed smaller improvement in finger-tapping skill across retention sleep than wakefulness, indicating that sleep-dependent procedural memory consolidation depends on developmental stage.     

The relationship between working memory capacity and cortical activity during performance of a novel motor task

ObjectivesThis study assessed whether individual differences in working memory capacity influenced verbal-analytical processes when performing a novel motor skill.DesignParticipants performed a tennis-hitting task in two conditions: no pressure and high-pressure.MethodsEighteen young adults participated in the study. EEG coherence between the T3-F3 and T4-F4 regions in the Beta1 and Alpha2 frequencies was recorded during performance in each condition. Verbal and visuo-spatial working memory capacity were assessed using the Automated Working Memory Assessment.ResultsNo differences were found between the two conditions for hitting performance and EEG activity. However, across both conditions, verbal and visuo-spatial working memory were significant predictors of EEG coherence between the T3-F3 and T4-F4 regions in the Beta1 and Alpha2 frequencies. Larger verbal working memory capacity was associated with greater coherence while the opposite trend was observed for visuo-spatial working memory capacity.ConclusionsThese results indicate that larger verbal working memory capacity is associated with a greater tendency to use explicit processes during motor performance, whereas larger visuo-spatial working memory capacity is associated more with implicit processes. The findings are discussed with relevance to the theory of implicit motor learning.     

Neuroimaging of declarative memory in schizophrenia

The past three decades have seen tremendous growth in our understanding of the cerebral underpinnings of schizophrenia. including the neural correlates of the cognitive impairment seen in this syndrome. In this article we review the role that structural and functional neuroimaging has played in elucidating the cerebral basis for the declarative memory deficits associated with schizophrenia. Memory impairment in schizophrenia appears to involve abnormal connectivity between the prefrontal cortex and three regions important in normal learning and memory: the hippocampus, thalamus, and cerebellum.     

Effects of delay of prospective memory cues in an ongoing task on prospective memory task performance

To address the mixed results reported in previous studies, the present experiments examined forgetting in prospective memory (PM) by manipulating the delay between the PM instructions and cue presentation in event-based PM tasks. PM performance was measured for delays of 2–20 min in Experiment 1 and for delays of approximately 1–10 min in Experiment 2. Experiment 2 included both focal and nonfocal PM tasks, and speed on the ongoing task was measured to examine evidence for monitoring processes across the delays tested. The results suggest that nonfocal PM performance follows a nonlinear forgetting function (i.e., rapid decline for shorter delays and slower decline for longer delays) when tested over delays from 1 to 20 min. No effect of delay was seen for the focal task tested in Experiment 2 from 1 to 10 min. In Experiment 2, ongoing-task costs were also found for the first delay but not for longer delays, suggesting that monitoring was significantly reduced between 1 and 2.5 min of the ongoing-task trials.     

Distinctiveness of processing,processing time and memory performance

The research reported here, explored the conditions where processing time can be used as a predictive measure for retention performance. The results showed that, in similar but quantitatively different tasks, both processing time and retention performance increased with increasing task difficulty. The strongly suggests that processing time can be used as an independent measure for extensiveness of processing, and as a predictor for later retention performance. This relationship, however, is restricted to the comparison of similar processing tasks that differ only in the amount of processing necessary to perform the task.It is hypothesized that longer processing times are indicative of more extensive processing, leading to the formation of more distinctive memory representations. These, in turn, cause higher retention performance because they allow better discrimination from other memory traces, and because they are retrieved more easily.Although distinctiveness of memory representations is an important variable in determining retention performance, it is not the only one. In a recall test, semantic relations between items had an effect on performance independent of distinctiveness.     

Information processing during general anesthesia: Evidence for unconscious memory

Memory for words presented during general anesthesia was studied in two experiments. In Experiment 1, surgical patients (n=80) undergoing elective procedures under general anesthesia were presented shortly before and during surgery with words via headphones. At the earliest convenient time after surgery (within 5 h) and 24 h later, memory was tested by asking patients to complete auditorily presented word stems with the first word that came to mind and to leave out words they remembered having heard earlier (exclusion task). Moreover, patients were requested to perform a “yes/no” forcedchoice recognition task to assess recognition memory for both the pre- and intraoperative words. Memory for the material presented during anesthesia was demonstrated immediately after surgery and 24 h later by means of both tasks. In a second similar experiment (n=80), the results were replicated. These findings show that anesthetized patients can process information that was presented intraoperatively.     

Acetylcholine release in hippocampus and striatum during testing on a rewarded spontaneous alternation task

The present experiment tested male Sprague-Dawley rats for spontaneous alternation performance in a food-rewarded Y-shaped maze. Microdialysis samples, later assessed for acetylcholine concentration, were collected from the hippocampus and striatum of each rat prior to and during testing; testing sessions lasted 20 min. Early in testing, rats alternated at a rate of 72%. Alternation scores increased throughout the 20-min testing session and reached 93% during the last 5 min. The behavioral findings suggest that, during testing, rats changed the basis for their performance from a spatial working memory strategy to a persistent turning strategy. ACh release in both hippocampus and striatum increased at the onset of testing. Increases in ACh release in the striatum began at 18% above baseline during the first 5 min of testing and steadily increased reaching 58% above baseline during the final 5 min. The progressive rise of striatum ACh release during testing occurred at about the time rats adopted a persistent turning strategy. In contrast, ACh release in the hippocampus increased by 50% with the onset of testing and remained at this level until declining slightly during the last 5 min of testing. The relative changes in ACh release in the striatum and hippocampus resulted in a close negative relationship between the ratio of ACh release in the hippocampus/striatum and alternation scores.     

Exploring memory in infancy: deferred imitation and the development of declarative memory

Imitation is an important means by which infants learn new behaviours. When infants do not have the opportunity to immediately reproduce observed actions, they may form a memory representation of the event which can guide their behaviour when a similar situation is encountered again. Imitation procedures can, therefore, provide insight into infant memory. The deferred imitation paradigm requires a modelled action to be reproduced following a delay, without prior motor practice. As such, deferred imitation procedures have been proposed to tap declarative memory abilities in non‐verbal populations such as infants. Contrary to the popular belief that infants form sparse or ill‐defined memories, deferred imitation research reveals that infants store and retrieve highly detailed memory representations. The specificity of detail encoded into the representation can, however, cause memory retrieval to fail at young ages. Developing the ability to identify event components which are central (the target stimulus) versus details which are peripheral (the exact context in which learning occurred) is therefore an important aspect of memory development. Using deferred imitation procedures to study the transition from constrained to flexible memory representations can thus facilitate our understanding of the development of declarative memory during the infancy period. Copyright © 2006 John Wiley & Sons, Ltd.     

Differences in performance of young and old monkeys on a visuospatial memory task

Two groups of stumptailed macaques (Macaca arctoides) were compared in terms of performance on a visuospatial working memory task involving repeated presentations of an array of 15 doors, each of which concealed one food reward at the start of a session. Rewards obtained by the subject were not replaced. Errors were defined as responses to doors previously pushed open during the session. Both groups generally obtained all rewards and showed improved performance across sessions, but old monkeys consistently made more errors than young ones, especially in the latter half of a given session. Further, old monkeys were less diverse in the errors they made, indicating different response strategies by the two groups.     

False memory in a short-term memory task

The Deese/Roediger-McDermott (DRM; Roediger & McDermott, 1995) paradigm reliably elicits false memories for critical nonpresented words in recognition tasks. The present studies used a Sternberg (1966) task with DRM lists to determine whether false memories occur in short-term memory tasks and to assess the contribution of latency data in the measurement of false memories. Subjects studied three, five, or seven items from DRM lists and responded to a single probe (studied or nonstudied). In both experiments, critical lures were falsely recognized more often than nonpresented weak associates. Latency data indicated that correct rejections of critical lures were slower than correct rejections of weakly related items at all set sizes. False alarms to critical lures were slower than hits to list items. Latency data can distinguish veridical and false memories in a short-term memory task. Results are discussed in terms of activation-monitoring models of false memory.     

Information processing by performers and observers in a paired associate learning task

The effects of two training procedures on learning and performance are compared. Performers select a response alternative for each stimulus on Trial 1 and receive feedback in terms of “Right” or “Wrong”. Observers receive the same information by listening to the experimenter. Experiment I tests the hypothesis that performers and observers are using a different learning strategy when there are only two response alternatives available for each stimulus on Trial 1. A recognition procedure was used on Trial 2; each stimulus was followed by four alternatives, two of them being the same as presented on Trial 1. Subjects have to recognize the two “old” alternatives. Performers are always better at recognizing the chosen alternative, whereas observers are better at recognizing the correct alternative. Experiment II extends the comparison between performers and observers to a task with four response alternatives on Trial 1. There are no longer differences in performance between the two training procedures.     

Intact conceptual priming in the absence of declarative memory

Priming is an unconscious (nondeclarative) form of memory whereby identification or production of an item is improved by an earlier encounter. It has been proposed that declarative memory and priming might be related-for example, that conceptual priming results in more fluent processing, thereby providing a basis for familiarity judgments. In two experiments, we assessed conceptual priming and recognition memory across a 5-min interval in 5 memory-impaired patients. All patients exhibited fully intact priming in tests of both free association (study tent; at test, provide an association to canvas) and category verification (study lemon; at test, decide: Is lemon a type of fruit?). Yet the 2 most severely amnesic patients performed at chance on matched tests of recognition memory. These findings count against the notion that conceptual priming provides feelings of familiarity that can support accurate recognition judgments. We suggest that priming is inaccessible to conscious awareness and does not influence declarative memory.