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PubMed2002

Visual object memory and memory-guided saccades rely on shared mental representations.

We investigated the organisation of working memory processes by examining how a secondary memory task interferes with the accuracy of memory-guided saccades. A target was flashed at a random location, followed by a Kanji character. Subjects had to remember the location of the target and the Kanji character, and then they had to make a saccade towards the remembered target location. A second Kanji character was displayed and the subject had to decide if it was same or different. The performance of seven non-Kanji reader's were compared with six fluent Kanji readers in the task. Memorisation of Kanji characters was found to interfere with the accuracy of memory-guided saccades made by non-Kanji, but not by Kanji readers. These findings directly contradict accounts of working memory function which propose that spatial and visual object memory are functionally discrete.

Adult↗

PubMed1988

Age-related deterioration of ability of acquisition in memory and learning in senescence accelerated mouse: SAM-P/8 as an animal model of disturbances in recent memory.

Memory, learning and behavior of senescence accelerated mouse (SAM-P/8) were investigated by using passive avoidance response, T-maze and open field and the findings were compared with those from senescence resistant mouse (SAM-R/1 control). SAM-P/8 mice showed a remarkable age-related deterioration in ability of memory and learning in passive avoidance response. This age-related memory and learning deficit was linked to a deterioration in the ability of acquisition and was not due to impairment in the ability of retention and hyperactivity, as observed in the open field. In the alternation T-maze tests, SAM-P/8 showed as high a rate of alternations as did the SAM-R/1 and in the T-maze avoidance tests, SAM-P/8 also showed as intact a memory ability as seen in the SAM-R/1, despite a memory deficit in the passive avoidance response. Thus, SAM-P/8 may prove to be a pertinent model for researching mechanisms related to the memory deficit seen in senile humans.

Aging↗

PubMed1978

Studies on memory: spontaneous return of memory in 6-hydroxydopamine-treated mice and its relation to cycloheximide-induced transient amnesia.

We suggested previously that cycloheximide-induced transient amnesia was due in part to side-effects of the antibiotic on the central adrenergic system at the time of testing and that spontaneous return of memory depended upon recovery of the adrenergic system. To test these possibilities, mice chronically depleted of brain catecholamines (CAs) by 6=hydroxydopamine (6-OHDA) were trained in an avoidance-discrimination task and tested for spontaneous return of memory. Contrary to our hypothesis, amnesia at 24 hr after training was followed by recovery of memory by 72 hr, which indicates that recovery of memory can occur independently of adrenergic recovery. Injection of alpha-methyl-para-tyrosine immediately after training prevented return of memory at 72 hr, suggesting that the residual CAs remaining after 6-OHDA are necessary for memory to spontaneously return at this time.

Amnesia↗

PubMed1987

Diazepam and memory: evidence for spared memory function.

The effects of diazepam on several tests of memory were investigated in a double-blind study of 24 healthy young adults. Following a single oral administration of 0.3 mg/kg diazepam or placebo, subjects in the diazepam group showed marked impairment in immediate free recall of words as compared to placebo control subjects. However, diazepam-treated subjects demonstrated performance benefits from prior exposure to the same words on tests of memory priming using word completion and category-generation tasks. The two types of memory tests differ in their demand for conscious recollection. Tests of free recall have explicit (declarative) memory demands whereas the priming test places only implicit (procedural) demands upon memory. The results demonstrate that diazepam spares some forms of memory as does amnesia induced by neurological impairment.

Adolescent↗

PubMed2005

Detecting simulated memory impairment: further validation of the Word Completion Memory Test (WCMT).

The Word Completion Memory Test (WCMT) was developed to detect sophisticated attempts at simulating memory impairment. The primary purpose of the present study was to provide additional validity and reliability information about the WCMT. Seventy-one participants were recruited for this study: 30 normal volunteers and 11 memory-disordered patients instructed to perform their best, and 30 normal volunteers instructed to fake memory impairment. Normal volunteers were administered five tests of neuropsychological functioning and five tests of simulation to explore the convergent and divergent validity of the WCMT. Two weeks later, these participants completed all 10 measures a second time. Memory-disordered patients were administered the WCMT and two additional simulation measures as part of a comprehensive neuropsychological evaluation. The WCMT successfully discriminated simulators from nonsimulators with an overall classification accuracy of 97% and demonstrated good psychometric properties. In conclusion, the WCMT continues to show promise as a measure of simulated memory impairment.

Adolescent↗

PubMed2005

Timing, memory for intervals, and memory for untimed stimuli: the role of instructional ambiguity.

Theories of animal timing have had to account for findings that the memory for the duration of a timed interval appears to be dramatically shorted within a short time of its termination. This finding has led to the subjective shortening hypothesis and it has been proposed to account for the poor memory that animals appear to have for the initial portion of a timed interval when a gap is inserted in the to-be-timed signal. It has also been proposed to account for the poor memory for a relatively long interval that has been discriminated from a shorter interval. I suggest here a simpler account in which ambiguity between the gap or retention interval and the intertrial interval results in resetting the clock, rather than forgetting the interval. The ambiguity hypothesis, together with a signal salience mechanism that determines how quickly the clock is reset at the start of the intertrial interval can account for the results of the reported timing experiments that have used the peak procedure. Furthermore, instructional ambiguity rather than memory loss may account for the results of many animal memory experiments that do not involve memory for time.

Animals↗

PubMed2006

The effects of memory load and stimulus relevance on the EEG during a visual selective memory search task: an ERP and ERD/ERS study.

OBJECTIVE: Psychophysiological correlates of selective attention and working memory were investigated in a group of 18 healthy children using a visually presented selective memory search task. METHODS: Subjects had to memorize one (load1) or 3 (load3) letters (memory set) and search for these among a recognition set consisting of 4 letters only if the letters appeared in the correct (relevant) color. Event-related potentials (ERPs) as well as alpha and theta event-related synchronization and desynchronization (ERD/ERS) were derived from the EEG that was recorded during the task. RESULTS: In the ERP to the memory set, a prolonged load-related positivity was found. In response to the recognition set, effects of relevance were manifested in an early frontal positivity and a later frontal negativity. Effects of load were found in a search-related negativity within the attended category and a suppression of the P3-amplitude. Theta ERS was most pronounced for the most difficult task condition during the recognition set, whereas alpha ERD showed a load-effect only during memorization. CONCLUSIONS: The manipulation of stimulus relevance and memory load affected both ERP components and ERD/ERS. SIGNIFICANCE: The present paradigm may supply a useful method for studying processes of selective attention and working memory and can be used to examine group differences between healthy controls and children showing psychopathology.

Attention↗

PubMed2006

Interfering with theories of sleep and memory: sleep, declarative memory, and associative interference.

Mounting behavioral evidence in humans supports the claim that sleep leads to improvements in recently acquired, nondeclarative memories. Examples include motor-sequence learning; visual-discrimination learning; and perceptual learning of a synthetic language. In contrast, there are limited human data supporting a benefit of sleep for declarative (hippocampus-mediated) memory in humans (for review, see). This is particularly surprising given that animal models (e.g.,) and neuroimaging studies (e.g.,) predict that sleep facilitates hippocampus-based memory consolidation. We hypothesized that we could unmask the benefits of sleep by challenging the declarative memory system with competing information (interference). This is the first study to demonstrate that sleep protects declarative memories from subsequent associative interference, and it has important implications for understanding the neurobiology of memory consolidation.

Adolescent↗

PubMed2004

Differences between recognition memory and remote memory for olfactory and visual stimuli in nondemented elderly individuals genetically at risk for Alzheimer's disease.

Recognition and remote memory for olfactory and visual stimuli were assessed in nondemented elderly individuals positive for the apolipoprotein E 4 allele and in 4 negative controls to examine whether the 4 allele differentially affects recognition and/or remote memory depending on the modality of stimulus to be remembered. Compared to controls, 4 positive individuals committed more false positive recognition memory errors for olfactory but not visual stimuli suggesting that 4 positive individuals may show false positive errors for olfactory stimuli before deficits for other stimuli are detectable. There were no significant differences in familiarity ratings (a proposed measure of remote memory) suggesting that brain areas involved in remote memory are not affected in nondemented 4 positive individuals. The results suggest that neuropathological changes in nondemented individuals genetically at risk for Alzheimer's disease may differentially affect memory processes.

Aged↗

PubMed2006

Simultaneous assessment of antigen-stimulated cytokine production and memory subset composition of memory CD8 T cells.

The functional identification of antigen-specific CD8 T cell populations is critical to understanding host responses to infection by intracellular pathogens. Furthermore, assessing the properties of protective memory CD8 T cell populations generated by immunization is necessary in the rational design of vaccines. Recently, a classification scheme was proposed in which memory CD8 T cells were divided into one of two distinct subsets, based on CD62L expression, that have different functional properties and protective capacities. Intracellular cytokine staining functionally identifies antigen-specific CD8 T cell populations after short in vitro stimulation with cognate peptide. This short stimulation, however, results in the cleavage of CD62L from the cell surface of antigen-specific CD8 T cells and precludes distinguishing CD62L(hi)- and CD62L(lo)-expressing memory cell subsets within this population. Here, we describe a method of preserving CD62L expression by the antigen-specific CD8 T cell population during coculture with antigen. This methodology allows for the identification and functional assessment of antigen-specific memory CD8 T cell populations, while simultaneously characterizing the memory subset composition of that population. Using this method, we directly identify differences in IL-2 production capacity by CD62L(hi)- and CD62L(lo)-expressing antigen-specific memory CD8 T cell populations.

Adoptive Transfer↗

PubMed2005

The case of K.C.: contributions of a memory-impaired person to memory theory.

K.C. has been investigated extensively over some 20 years since a motorcycle accident left him with widespread brain damage that includes large bilateral hippocampal lesions, which caused a remarkable case of memory impairment. On standard testing, K.C.'s anterograde amnesia is as severe as that of any other case reported in the literature, including H.M. However, his ability to make use of knowledge and experiences from the time before his accident shows a sharp dissociation between semantic and episodic memory. A good deal of his general knowledge of the world, including knowledge about himself, is preserved, but he is incapable of recollecting any personally experienced events. In displaying such "episodic amnesia," which encompasses an entire lifetime of personal experiences, K.C. differs from many other amnesic cases. Here, we document for the first time the full extent of K.C.'s brain damage using MRI-based quantitative measurements. We then review the many investigations with K.C. that have contributed to our understanding not only of episodic and semantic memory but also to the development of other aspects of memory theory. These include the distinction between implicit and explicit memory, the prospect of new learning in amnesia, and the fate of recent and remote memory for autobiographical and public events, people, and spatial locations.

Adult↗

PubMed2006

Deficits in memory strategy use are related to verbal memory impairments in adolescents with schizophrenia-spectrum disorders.

OBJECTIVE: To assess the nature of learning and verbal memory deficits in adolescents with schizophrenia-spectrum disorders (SzS) (i.e., schizophrenia, schizoaffective disorder, and schizophreniform disorder). METHOD: Sixty patients with SzS (mean age=16.1 years, S.D. = 2.2) and 60 age- and gender-matched diagnosis-free healthy volunteers were assessed using the California Verbal Learning Test (CVLT). Planned analyses were conducted to assess the following aspects of memory: span of apprehension, verbal learning, short-term and long-term memory, rate of forgetting, interference, and organizational strategies. Adolescents with schizophrenia (Sz) were compared to those with schizoaffective disorder (SzA). Second, patients' test profiles were compared to those of controls. Relationships between initial learning and overall verbal learning with organizational strategy were explored. RESULTS: Neurocognitive profiles did not significantly differ between Sz and SzA participants. Patients performed significantly worse than healthy comparison subjects on measures of span of apprehension, verbal learning, short- and long-term memory, and organizational strategies after adjusting for differences in premorbid intelligence. No group differences were found in rate of forgetting or susceptibility to proactive or retroactive interference. CONCLUSIONS: Adolescents with SzS are characterized by significant verbal memory dysfunction similar to what has been observed in adults with first-episode schizophrenia. Deficits in consistency of learning over several trials, as well as a strong relationship between semantic organizational strategies and reduced learning capacity, implicate dysfunction of the dorsolateral prefrontal cortex as a contributor to verbal memory deficits in adolescents with SzS.

Adolescent↗

PubMed2005

Computational models of working memory: putting long-term memory into context.

Detailed computational modeling of human memory has typically been aimed at either short-term (working) memory or long-term memory in isolation. However, recent research highlights the importance of interactions between these systems for both item and order information. At the same time, computational models of both systems are beginning to converge onto a common framework in which items are associated with an evolving "context" signal and subsequently compete with one another at recall. We review some of these models, and discuss a common mechanism capable of modelling working memory and its interaction with long-term memory, focussing on memory for verbal sequences.

Attention↗

PubMed1984

Investigation of everyday memory in normal subjects using the Subjective Memory Questionnaire (SMQ).

This study examined memory for everyday events by method of self-report using the Subjective Memory Questionnaire (SMQ). The purpose of the study was to repeat and extend existing normative data. The SMQ was found to be adequately reliable, but this finding needs to be replicated in a large sample of subjects. Data from 170-224 control subjects revealed no effects of age or sex on total SMQ scores. However, sex differences occurred in 50% of individual questions, possibly reflecting cultural stereotypes. Higher social classes rated their memory more optimistically than lower classes. Overall subjects estimated their memory as being above "average". Principal Component Analysis revealed 10 factors with eigen-values greater than 1.0. These included factors for "male" and "female" memory that have not been found previously in studies using subjective measures of everyday memory. Factors identified as "absentmindedness", "names" and "how to get somewhere" were similar to those reported elsewhere.

Adolescent↗

PubMed2000

Medial temporal atrophy and memory impairment in early stage of Alzheimer's disease: an MRI volumetric and memory assessment study.

Memory impairment and medial temporal lobe (MTL) involvement are the earliest and most prominent features of Alzheimer's disease (AD). A psychological assessment of memory function and an evaluation of the morphological changes in MTL structures, as found in the mild form of AD, are important for early diagnosis as well as for understanding the pathophysiology of the disease. In the present study, we aimed to evaluate correlations in these psychoanatomical changes in terms of the stage of AD. We performed MRI-based volumetric measurements of the MTL structure and neuropsychological tests, using MMSE and the Wechsler memory scale-revised (WMS-R), on 27 elderly normal subjects and 46 probable AD patients, and then checked for possible correlations between the volumetric measurements and memory dysfunction. The severity of the AD patients' condition was assessed by CDR scale. Each MTL structure decreased in volume with increasing severity of AD. In very early AD, the reduction in the amygdala volume was pronounced, while the hippocampal volumes were relatively unchanged. Neuropsychological scores also declined with increasing severity of AD. Scores on the main WMS-R subsets examined (verbal memory, visual memory, and delayed recall) decreased significantly in the very mild group, as compared with normal controls. The WMS-R test scores correlated significantly with the amygdala volumes in normal control subjects and very mild AD patients. Our findings suggest that MRI-based amygdaloid volumetric measurement provides a sensitive marker, and that the degeneration of the amygdala may begin very early in the course of AD.

Aged↗

PubMed2002

Hypothalamic-pituitary-adrenal axis reactivity to psychological stress and memory in middle-aged women: high responders exhibit enhanced declarative memory performance.

According to recent studies, elevated cortisol levels are associated with impaired declarative memory performance. This specific effect of cortisol has been shown in several studies using pharmacological doses of cortisol. The present study was designed to determine the effects of endogenously stimulated cortisol secretion on memory performance in healthy middle-aged women. For psychological stress challenging, we employed the Trier Social Stress Test (TSST). Subjects were assigned to either the TSST or a non-stressful control condition. Declarative and non-declarative memory performance was measured by a combined priming-free-recall-task. No significant group differences were found for memory performance. Post hoc analyses of variance indicated that regardless of experimental condition the subjects with remarkably high cortisol increase in response to the experimental procedure (high responders) showed increased memory performance in the declarative task compared to subjects with low cortisol response (low responders). The results suggest that stress-induced cortisol failed to impair memory performance. The results are discussed with respect to gender-specific effects and modulatory effects of the sympathetic nervous system and psychological variables.

Adult↗

PubMed2003

Evidence for the substantia nigra pars compacta as an essential component of a memory system independent of the hippocampal memory system.

The aim of the present study was to test if the nigrostriatal pathway is an essential component for a water maze cued task learning and if it works independently of the hippocampal memory system. This hypothesis was tested using an animal model of Parkinson's disease in which male Wistar rats were lesioned in the substantia nigra pars compacta (SNc) by the intranigral infusion of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), thus causing a partial depletion of striatal dopamine. SNc-lesioned and sham-operated animals were implanted bilaterally with guide cannulae above the dorsal hippocampus in order to be tested after the administration of 0.4 microl 2% lidocaine or saline into this structure. The animals were tested in a spatial or in a cued version of the water maze, memory tasks previously reported to model hippocampal-dependent spatial/relational and striatal-dependent S-R learning, respectively. Hippocampal inactivation, but not SNc lesion, impaired learning and memory in the spatial version of the water maze. An opposite situation was observed with the cued version. No significant interaction was observed between the SNc lesion and hippocampal inactivation conditions affecting scores in the spatial or in the cued version of the water maze. These results suggest that the nigrostriatal pathway is an essential part of the memory system that processes S-R learning and that it works independently of the hippocampal memory system that processes spatial/relational memories.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMed2003

Role of cholinergic system on the construction of memories: taste memory encoding.

There is a large body of evidence suggesting that cholinergic activity is involved in memory processes. It seems that cholinergic activity is essential to learn several tasks and recent works suggest that acetylcholine plays an important role during the early stages of memory formation. In this review, we will discuss the results related to taste memory formation, focusing particularly on the conditioned taste aversion paradigm. We will first give evidence that nucleus basalis magnocellularis is involved in taste memory formation, due to its cholinergic projections. We then show that the cholinergic activity of the insular (gustatory) cortex is related to the taste novelty, and that the cholinergic signals initiated by novelty are crucial for taste memory formation. Then we present recent data indicating that cortical activation of muscarinic receptors is necessary for taste trace encoding, and also for its consolidation under certain circumstances. Finally, interactions between the cholinergic and other neuromodulatory systems inducing intracellular mechanisms related to plastic changes will be proposed as important processes underlying gustatory memory trace storage.

Amygdala↗