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PubMed1986

Aged rats need a preserved complement of perforated axospinous synapses per hippocampal neuron to maintain good spatial memory.

Spatial working memory, which crucially depends on the structural integrity of the hippocampal formation and its afferent connections, is impaired in the most, but not all, of aged rats. This study was designed to verify whether aged animals that do not exhibit the spatial memory deficit are the ones in which the hippocampal synaptic connectivity remains preserved with advancing chronological age. Young adult rats with good spatial memory, aged rats with impaired spatial memory and equally aged rats with intact spatial memory were compared. The number of synapses per neuron was estimated in the hippocampal dentate gyrus. The most important results were obtained when axospinous synapses were divided into perforated and non-perforated ones according to the appearance of their postsynaptic density. A significant decrease in the number of perforated synapses was found in memory-impaired aged rats as compared to either young adults or aged animals without memory deficits. The number of non-perforated synapses per neuron was diminished in memory-deficient aged rats relative to young adults, but not to memory-intact aged rats. However, it was only the loss of perforated synapses which correlated with the degree of spatial memory impairment. Thus, aged rats need a preserved complement of hippocampal perforated synapses to maintain good spatial memory.

Aging↗

PubMed1996

Brain potentials before and during memory scanning.

Brain potentials were recorded from 10 normal subjects engaged in a 3-item auditory verbal short-term memory task. A fixed interval (3 s) between the last memory item and the probe was compared to a random interval (1.8-4.2 s with a mean of 3 s). Subjects indicated by button press whether the probe was or was not a member of the memory-set. The same 3-item task was also presented as a counting task and required a button press to the "fourth stimulus' (the probe). The amplitudes of several slow potential shifts preceding and following the probe, and the amplitudes and latencies of the accompanying short duration components (N100, P200) were measured. When the probe appeared at a fixed interval, the amplitude of a slow negative potential in the 300 ms period preceding the probe was slightly larger in the memory than in the counting task. When the probe appeared at a random interval in the memory task, the slow negative shift preceding the probe was absent. Another slow negative shift that peaked at approximately 376 ms after the probe was present in the memory tasks but was absent in the counting task. The amplitude of a late positive shift that peaked at approximately 700 ms after the probe was not different within the memory tasks, or between the memory and counting tasks. N100 amplitude but not P200 amplitude was larger in the memory task when the probe occurred at a fixed than at a random interval. These results suggest that the amplitude of a slow negative shift preceding the probe was related primarily to a temporal expectancy for the appearance of the probe and to a lesser extent to memory processes. In contrast, a slow negative shift that followed the probe occurred only during the memory tasks.

Adult↗

PubMed2006

Memory and metamemory for semantic information in obsessive-compulsive disorder.

Several studies have been conducted on OCD patients' memory and metamemory performance in episodic tasks. However, there is a clear lack of research addressing these issues for semantic memory (i.e., retrieval of information from long-term memory). Although findings regarding a memory deficit is somewhat equivocal, the empirical evidence clearly demonstrates that OCD patients with primarily checking compulsions show reduced confidence in their memory performance. The purpose of the present study was to investigate memory and metamemory performance of checkers in semantic memory domain. We compared checker OCD patients, non-checker OCD patients and normal controls on their ability to retrieve answers to general knowledge questions with a recall as well as a recognition test. We also investigated prospective (feeling-of-knowing (FOK)) and retrospective (confidence) metamemory judgments. Checker OCs were not poorer in retrieving semantic information from long-term memory. Neither were they less confident about their ability to remember currently unrecallable information in the future (FOK judgments) or about the accuracy of retrieved information (confidence judgments). Moreover, accuracy of metamemory judgments were comparable across groups. Overall, our results revealed that checker OCs do not show a memory or metamemory deficit when semantic memory was concerned, suggesting that any memory and metamemory deficit may be special to recently experienced materials.

Adult↗

PubMed2004

Self-rated everyday and prospective memory abilities of cigarette smokers and non-smokers: a web-based study.

The present study examined self-ratings of two aspects of everyday memory performance: long-term prospective memory-measured by the prospective memory questionnaire (PMQ), and everyday memory-measured by the everyday memory questionnaire (EMQ). Use of other substances was also measured and used as covariates in the study. To ensure confidentiality and to expand the numbers used in previous studies, an Internet study was carried out and data from 763 participants was gathered. After controlling for other drug use and strategy use, the data from the PMQ revealed that smokers reported a greater number of long-term prospective memory errors than non-smokers. There were also differences between light and heavier smokers in long-term prospective memory, suggesting that nicotine may have a dose-dependent impact upon long-term prospective memory performance. There was also a significant ANOVA group effect on the EMQ, although the trend for more memory errors amongst the heavier smokers was statistically only borderline (p=.057). These findings suggest there are selective memory deficits associated with smoking and that long-term prospective memory deficits should be added to the growing list of problems associated with cigarette use.

Adult↗

PubMed2005

Emotional memory is perceptual.

In two experiments it was investigated which aspects of memory are influenced by emotion. Using a framework proposed by Roediger (American Psychologist 45 (1990) 1043-1056), two dimensions relevant for memory were distinguished the implicit-explicit distinction, and the perceptual versus conceptual distinction. In week 1, subjects viewed a series of slides accompanied with a spoken story in either of the two versions, a neutral version, or a version with an emotional mid-phase. In week 2, memory performance for the slides and story was assessed unexpectedly. A free recall test revealed superior memory in the emotional condition for the story's mid-phase stimuli as compared to the neutral condition, replicating earlier findings. Furthermore, memory performance was assessed using tests that systematically assessed all combinations of implicit versus explicit and perceptual versus conceptual memory. Subjects who had listened to the emotional story had superior perceptual memory, on both implicit and explicit level, compared to those who had listened to the neutral story. Conceptual memory was not superior in the emotional condition. The results suggest that emotion specifically promotes perceptual memory, probably by better encoding of perceptual aspects of emotional experiences. This might be related to the prominent position of perceptual memories in traumatic memory, manifest in intrusions, nightmares and reliving experiences.

Adult↗

PubMed2003

Synchronous loss of quasispecies memory in parallel viral lineages: a deterministic feature of viral quasispecies.

Viral quasispecies are endowed with a memory of their past evolutionary history in the form of minority genomes of their mutant spectra. To determine the fate of memory genomes in evolving viral quasispecies, we have measured memory levels of antigenic variant of foot-and-mouth disease virus (FMDV) RED, which includes an Arg-Glu-Asp (RED) at a surface antigenic loop of the viral capsid. The RED reverted to the standard Arg-Gly-Asp (RGD), and the RED remained as memory in the evolving quasispecies. In four parallel evolutionary lineages, memory reduction followed a strikingly similar pattern, and at passage 60 memory levels were indistinguishable from those of control populations (devoid of memory). Nucleotide sequence analyses indicated that memory loss occurred synchronously despite its ultimate molecular basis being the stochastic occurrence of mutations in the evolving quasispecies. These results on the kinetics of memory levels have unveiled a deterministic feature of viral quasispecies. Molecular mechanisms that may underlie synchronous memory loss are the averaging of noise signals derived from mutational input, and constraints to genome diversification imposed by a nucleotide sequence context in the viral genome. Possible implications of the behaviour of complex, adaptive viral systems as experimental models to address primary mechanisms of neurological memory are discussed.

Amino Acid Sequence↗

PubMed2005

Memory performance in late pregnancy and erythrocyte indices.

OBJECTIVE: A previous study in elderly people observed an association between chronologically younger erythrocyte population and memory impairment. The aim of this study was to assess whether a similar shift in erythrocyte population in pregnant women in late pregnancy is associated with changes in memory performance in healthy pregnant women. METHODS: Thirty healthy pregnant women were included in a prospective cross-sectional study. Explicit memory and autobiographic memory tests were performed in the late third trimester and 4 months postpartum. Mean corpuscular volume (MCV) was considered the primary predictor variable. RESULTS: The mean explicit memory recall scores were significantly higher at post-delivery compared to pre-delivery: 8.3 +/- 1.7 and 7.4 +/- 1.4, respectively (P = .015). The difference in mean autobiographic memory test score pre- and post-delivery did not reach statistical significance. A positive correlation between post-delivery explicit memory recall scores and the difference between pre- and post-delivery MCV was detected (r = 0.458, P = .01). The correlation between delta MCV and delta explicit memory recall scores was r = 0.2, P =.311. Pre-delivery autobiographic memory test scores were positively correlated with MCV (r = 0.50, P = .006), mean corpuscular hemoglobin (r = 0.57, P = .001), and mean corpuscular hemoglobin concentration (r = 0.46, P = .013). CONCLUSION: The change in erythrocyte population that is present in late pregnancy predicted explicit memory performance after delivery, when it was improved. The younger erythrocyte population that exists in late pregnancy is associated with a better autobiographic memory.

Adolescent↗

PubMed2006

Evidence for preferential Ig gene usage and differential TdT and exonuclease activities in human naïve and memory B cells.

Memory B cells and the antibodies they encode are important for protective immunity against infectious pathogens. Characterization of naïve and memory B cell antibody repertoires will elucidate the molecular basis for the generation of antibody diversity in human B cells and the optimization of antibody structures that bind microbial antigens. In this study we aimed to investigate the influence of antigenic selection on the antibody genes of the two CD27+ memory B cell subsets, comparing them with the naïve repertoire in CD27- cells. We analyzed and compared the Ig heavy chain gene transcripts in three recently defined circulating naïve and memory B cell subsets (CD19+IgD+CD27- [naïve], CD19+IgD+CD27+ [un-class-switched memory] or CD19+IgD- CD27+ [class-switched memory]) at the single cell level. We found similar biased patterns of variable, diversity and joining heavy chain gene usages in all three groups of cells. CD19+IgD+CD27+ memory B cells harbored as diverse an antibody gene repertoire as CD19+IgD-CD27+ memory B cells. Interestingly, CD19+IgD+CD27+ memory B cells possessed a lower frequency of somatic mutations, a higher incidence of exonuclease activity at the 3' end of D regions, and a lower frequency of N and P nucleotide additions at both VH-D and D-JH junctions of CDR3 regions compared to CD19+IgD-CD27+ memory B cells. These data suggest distinct functional mechanisms underlying selection of this unique subset of un-class-switched memory B cells.

Adult↗

PubMed2006

Brain oscillatory 1-30 Hz EEG ERD/ERS responses during the different stages of an auditory memory search task.

Event-related desynchronization (ERD) and event-related synchronization (ERS) responses of 1-30 Hz EEG frequencies during the different stages of an auditory Sternberg memory task were examined. The ERD/ERS responses were examined separately for successive memory set items (four) and for the two recognition conditions (YES/NO). The presentation of the memory set elicited ERS responses in the theta and alpha frequencies, and also beta ERD responses. These ERD/ERS responses elicited during encoding were found to evolve with successive memory set item presentation. The ERD/ERS responses elicited during the presentation of the probe dissociated significantly between the two recognition conditions (YES/NO). When the probe was included in the memory set (YES condition), recognition elicited stronger alpha and beta frequency ERD responses as compared to the NO condition. The findings from the current study verify that alpha ERD/ERS responses robustly dissociate between auditory encoding and recognition. The increasing alpha ERS responses with increasing memory set item presentation during encoding may be correlates of the functioning phonological loop, active memory maintenance and/or attention. The alpha ERD responses during recognition are undoubtedly associated with auditory memory search processes and distinguish between previously presented versus not presented verbal material. We propose that alpha ERD/ERS responses reflect explicitly auditory memory processes, discriminating between auditory encoding and recognition. Theta ERS responses may be associated with working memory processes, and possibly more specifically with the functioning of the central executive. Beta ERD/ERS responses may reflect also cognitive and/or memory processing, rather than merely the activity of the motor cortices.

Acoustic Stimulation↗

PubMed2005

Individual differences in working memory.

Working memory can be defined as the ability to hold in mind information in the face of potentially interfering distraction in order to guide behavior. The experimental manipulation of working memory tasks has shed considerable light on the probable structure of the human working memory system, and, to a lesser extent, the specific processes captured by working memory paradigms. However, individual differences research has also had a crucial role to play in the development of theories of working memory. In particular, correlational approaches have been particularly informative in three areas of working memory research, each of which is reviewed here. These are, first, the importance of working memory measures as correlates of high-level cognitive skills such as reading, mathematics, reasoning, and fluid intelligence; second, the extent to which human working memory relies on domain-general or domain-specific component subsystems, and third, the precise reasons why working memory measures do relate to other important indices of human cognitive functioning. The findings from each of these areas suggest that working memory depends on a combination of domain-specific representational systems and domain-general processing and control systems, and that working memory measures capture individuals' ability to combine maintenance and processing demands in a manner that limits information loss from forgetting or distraction.

Brain↗

PubMed2005

Post-training N-methyl-D-aspartate receptor blockade offers protection from retrograde interference but does not affect consolidation of weak or strong memory traces in the water maze.

Memory consolidation is the process where labile memory traces become long-lasting, stable memories. Previous work has demonstrated that spatial memory consolidation, several days after training in a water maze had ceased, can be disrupted by a temporary intra hippocampal infusion of the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate antagonist LY326325 (Riedel et al., 1999). Such reversible pharmacological techniques offer advantages over the permanent lesion studies that had first suggested a role for the hippocampus in memory consolidation. However, to date the role of N-methyl-D-aspartate receptors in such systems level processes remains controversial with evidence for impairments and augmentation of performance. Here we investigate the role of post-training hippocampal N-methyl-D-aspartate receptor blockade in rats and mice on the consolidation of weak and strong memory traces using an Atlantis water maze protocol. A hidden Atlantis platform was employed and rats (experiments 1 and 2) and mice (experiment 3) were required to dwell within 20 cm of the trained location to activate and subsequently reveal the escape platform. In experiments 1 and 3 a strong memory trace was established by training rats or mice for several days in the water maze. In experiment 2 a significantly weaker trace was instituted by reducing the training period. N-methyl-D-aspartate receptor blockade was induced after the last training trial and continued for seven days. Reliable memory for the trained platform location in a retention test 15 days after the last training day demonstrated that N-methyl-D-aspartate receptor blockade did not affect memory consolidation in rats or mice. Our results also show that post-training N-methyl-D-aspartate receptor blockade can lead to better performance in further retention tests conducted after the consolidation and drug administration period. Those data suggest that specific post-training N-methyl-D-aspartate receptor blockade does not impair memory consolidation and it may also offer a memory trace mild protection from retrograde interference.

Animals↗

PubMed2003

Systems mediating acute glucocorticoid effects on memory consolidation and retrieval.

It is well established that glucocorticoid hormones, secreted by the adrenal cortex after a stressful event, influence cognitive performance. This article reviews recent findings from this laboratory on the acute effects of glucocorticoids in rats on specific memory phases, i.e., memory consolidation and memory retrieval. Posttraining activation of glucocorticoid-sensitive pathways involving glucocorticoid receptors (GRs) enhances memory consolidation in a dose-dependent manner. Glucocorticoid influences on memory consolidation depend on noradrenergic activation of the basolateral complex of the amygdala (BLA) and interactions of the BLA with other brain regions. By contrast, memory retrieval processes are usually impaired with high circulating levels of glucocorticoids or following infusions of GR agonists into the hippocampus. Although the BLA does not appear to be a site of glucocorticoid action in influencing memory retrieval, an intact BLA is required for enabling glucocorticoid effects on memory retrieval. The BLA appears to be a key structure in a memory-modulatory system that regulates, in concert with other brain regions, stress and glucocorticoid effects on both memory consolidation and memory retrieval.

Amygdala↗

PubMed2004

Cognitive and psychological predictors of everyday memory in children with intractable epilepsy.

Children with epilepsy have known deficits on objective measures of learning and memory. Parents and children report that memory deficits have a negative impact on everyday functioning. In adults with epilepsy, self-report of memory is more strongly associated with depression than performance on memory tests. We investigated the cognitive and psychological predictors of everyday memory in 37 children with medically intractable epilepsy, using children's self-report and parent ratings of everyday memory performance and standard tests of attention, intelligence, visual and verbal memory, working memory, and mood/emotional state. Standard multiple regressions demonstrated that only a parent report measure of attention uniquely and significantly (P< or =0.05) predicted estimates of everyday memory performance, accounting for 33% of variance in children's own ratings and 27% of variance in parents' ratings. Findings suggest that everyday memory in children with intractable epilepsy differs from that of adults; attentional problems may underlie everyday memory problems in these children.

Adolescent↗

PubMed2001

Memory bias, confidence and responsibility in compulsive checking.

Recent research suggests that there is a positive memory bias for threatening information in compulsive cleaners. However, the relationship between OCD and memory is likely to be more complex when the compulsive behaviour is checking. Hence, we decided to explore this relationship in a clinical sample of people who check compulsively. Participants completed a diagnostic interview and were then asked to complete a standard 'baseline' check which normally causes distress/discomfort. Two additional checks were then completed--one under conditions of high responsibility and one under low responsibility. The order of responsibility manipulation was randomized across participants. After each check, participants completed a Memory and Confidence Interview which assessed memory for threat-relevant and threat-irrelevant aspects of the check, and also confidence in memory for the check. One week later, participants came into the laboratory to complete additional Memory and Confidence Interviews after watching a videotape of the checks completed earlier in their own homes. These videotaped checks were taken as conditions of 'no responsibility'. Results show a positive memory bias for threat-relevant information. As responsibility was inflated, this positive memory bias was amplified. Under conditions of no responsibility, no memory bias was detectable. Also, responsibility appears to have had a greater impact on confidence in memory than on memory itself in OCD. The results are discussed in terms of the mnestic deficit theory of OCD and in terms of cognitive-behavioural approaches to understanding the disorder.

Adult↗

PubMed2002

Conscious and unconscious uses of memory in multiple sclerosis.

Conscious and unconscious uses of memory and priming were studied in 30 patients with multiple sclerosis (MS) and 15 normal control (NC) subjects. MS patients were classified into two subgroups according to their cognitive status; 15 of them were cognitively deteriorated (the MS-D group) and 15 cognitively preserved (the MS-P group). A process dissociation procedure [J. Mem. Lang. 30 (1991) 513] was used to separate conscious and unconscious memory performance in a word stem completion task. The results showed that the MS-D group had deficient conscious memory performance, but had intact unconscious memory as well as priming. The MS-P group showed normal conscious and unconscious uses of memory and priming. Thus, in MS-related cognitive decline, conscious memory seems to be vulnerable, whereas unconscious memory remains intact. The results provide neuropsychological support for the distinction between conscious and unconscious memory processes. Moreover, the results show the importance of studying cognitively homogenous MS groups as opposed to heterogenous ones, in order to find the underlying mechanisms of memory deficits in MS. Interestingly, the neural systems needed for the unconscious use of memory do not seem to deteriorate even in MS patients with deficient overall cognitive capacity. This finding encourages the development of future rehabilitation programs, suggesting that unconscious remembering might help MS patients with deficient conscious memory to cope with their daily activities.

Adult↗

PubMed2003

Effects of repetitive transcranial magnetic stimulation on memory subtypes: a controlled study.

Repetitive transcranial magnetic stimulation (rTMS) of human cortex may disrupt or facilitate cortical activity. The aim of the present study was to investigate the consequences of rTMS applied over different cortical areas during various memory tasks, measuring immediate, working and episodic verbal memory. The study was performed in 16 right-handed healthy men. A double-blind, cross-over, within-subject repeated measures design was used. There were five rTMS conditions: baseline without stimulation, high frequency (HF) rTMS over right and left dorsolateral prefrontal cortex (DLPFC) and over right cerebellum, and low frequency (LF) parameters over left DLPFC. Digits forwards and backwards and letter-number sequencing of the Wechsler Adults Intelligence Scale (WAIS) were used to assess immediate and working verbal memory, and logical memory of the Rivermead Behavioural Memory Test was used to assess episodic memory encoding. An analysis of variance (ANOVA) for repeated measures in the scores of each memory task according to rTMS conditions was used. Significantly lower scores in the number of memory units of the episodic memory task were observed when rTMS high frequency parameters were applied over left DLPFC (P=0.009). No significant differences were found in the other memory subtype tasks analysed during the different rTMS conditions. These findings provide evidence for the significant role of the left DLPFC in episodic verbal memory processes.

Adult↗

PubMed1998

Double dissociation of processing temporal and spatial information in working memory.

Based on the converging evidence supporting the view of domain specific object and spatial working memory processes, the question was addressed whether the property of domain specificity holds equally for temporal information. Using a selective interference paradigm the objective was to test a dissociation of the processing of temporal duration and spatial location information in working memory of intact human subjects. Subjects performed a temporal and a spatial memory task in which they were required to indicate whether the study and the test stimuli were the same or different in duration (temporal memory) or in location (spatial memory) as primary tasks. Both primary tasks were combined with three types of interference tasks, a spatial classification memory task, a temporal classification memory task and a non-interference baseline task--to be performed in-between the presentation of study and test stimuli. Memory for temporal duration was shown to be impaired by the temporal classification task but not by the spatial classification task; memory for spatial position showed the opposite pattern of impairment. These data thus provide evidence for the view that temporal and spatial working memory contents are subject to selective interference, reflecting a functional dissociation in the processing of temporal duration and spatial location information. The results are interpreted as evidence for the domain specificity in the processing of temporal information in working memory.

Adult↗

PubMed2000

Cortical dynamics of memory.

Memory networks are formed in the cerebral cortex by associative processes, following Hebbian principles of synaptic modulation. Sensory and motor memory networks are made of elementary representations in cell assemblies of primary sensory and motor cortex (phyletic memory). Higher-order individual memories, e.g. episodic, semantic, conceptual - are represented in hierarchically organized neuronal networks of the cortex of association. Perceptual memories are organized in posterior (post-rolandic) cortex, motor (executive) memories in cortex of the frontal lobe. Memory networks overlap and interact profusely with one another, such that a cellular assembly can be part of many memories or networks. Working memory essentially consists in the temporary activation of a memory network, as needed for the execution of successive acts in a temporal structure of behavior. That activation of the network is maintained by recurrent excitation through reentrant circuits. The recurrent reentry may occur within local circuits as well as between separate cortical areas. In either case. recurrence binds together the associated components of the network and thus of the memory it represents.

Animals↗