A Common Task Structure Links Together the Fate of Different Types of Memories

Our memories frequently have features in common. For example, a learned sequence of words or actions can follow a common rule, which determines their serial order, despite being composed of very different events [1, 2]. This common abstract structure might link the fates of memories together. We tested this idea by creating different types of memory task: a sequence of words or actions that either did or did not have a common structure. Participants learned one of these memory tasks and then they learned another type of memory task 6 h later, either with or without the same structure. We then tested the newly formed memory's susceptibility to interference. We found that the newly formed memory was protected from interference when it shared a common structure with the earlier memory. Specifically, learning a sequence of words protected a subsequent sequence of actions learned hours later from interference, and conversely, learning a sequence of actions protected a subsequent sequence of words learned hours later from interference provided the sequences shared a common structure. Yet this protection of the newly formed memory came at a cost. The earlier memory had disrupted recall when it had the same rather than a different structure to the newly formed and protected memory. Thus, a common structure can determine what is retained (i.e., protected) and what is modified (i.e., disrupted). Our work reveals that a shared common structure links the fate of otherwise different types of memories together and identifies a novel mechanism for memory modification.

Not explicit but implicit memory is influenced by individual perception style

Not only explicit but also implicit memory has considerable influence on our daily life. However, it is still unclear whether explicit and implicit memories are sensitive to individual differences. Here, we investigated how individual perception style (global or local) correlates with implicit and explicit memory. As a result, we found that not explicit but implicit memory was affected by the perception style: local perception style people more greatly used implicit memory than global perception style people. These results help us to make the new effective application adapting to individual perception style and understand some clinical symptoms such as autistic spectrum disorder. Furthermore, this finding might give us new insight of memory involving consciousness and unconsciousness as well as relationship between implicit/explicit memory and individual perception style.

BDNF val66met polymorphism affects aging of multiple types of memory

The BDNF val66met polymorphism (rs6265) influences activity-dependent secretion of brain-derived neurotrophic factor in the synapse, which is crucial for learning and memory. Individuals homozygous or heterozygous for the met allele have lower BDNF secretion than val homozygotes and may be at risk for reduced declarative memory performance, but it remains unclear which types of declarative memory may be affected and how aging of memory across the lifespan is impacted by the BDNF val66met polymorphism. This cross-sectional study investigated the effects of BDNF polymorphism on multiple indices of memory (item, associative, prospective, subjective complaints) in a lifespan sample of 116 healthy adults aged 20-93 years. Advancing age showed a negative effect on item, associative and prospective memory, but not on subjective memory complaints. For item and prospective memory, there were significant age×BDNF group interactions, indicating the adverse effect of age on memory performance across the lifespan was much stronger in the BDNF met carriers than for the val homozygotes. BDNF met carriers also endorsed significantly greater subjective memory complaints, regardless of age, and showed a trend (p<.07) toward poorer associative memory performance compared to val homozygotes. These results suggest that genetic predisposition to the availability of brain-derived neurotrophic factor, by way of the BDNF val66met polymorphism, exerts an influence on multiple indices of episodic memory - in some cases in all individuals regardless of age (subjective memory and perhaps associative memory), in others as an exacerbation of age-related differences in memory across the lifespan (item and prospective memory). This article is part of a Special Issue entitled Memory & Aging.

Time scales of memory, learning, and plasticity

After only about 10 days would the storage capacity of our nervous system be reached if we stored every bit of input. The nervous system relies on at least two mechanisms that counteract this capacity limit: compression and forgetting. But the latter mechanism needs to know how long an entity should be stored: some memories are relevant only for the next few minutes, some are important even after the passage of several years. Psychology and physiology have found and described many different memory mechanisms, and these mechanisms indeed use different time scales. In this prospect we review these mechanisms with respect to their time scale and propose relations between mechanisms in learning and memory and their underlying physiological basis.

Expression profiling reveals differential gene induction underlying specific and non-specific memory for pheromones in mice

Memory for the mating male's pheromones in female mice is thought to require synaptic changes in the accessory olfactory bulb (AOB). Induction of this memory depends on release of glutamate in response to pheromonal exposure coincident with release of norepinephrine (NE) in the AOB following mating. A similar memory for pheromones can also be induced artificially by local infusion of the GABA(A) receptor antagonist bicuculline into the AOB. The natural memory formed by exposure to pheromones during mating is specific to the pheromones sensed by the female during mating. In contrast, the artificial memory induced by bicuculline is non-specific and results in the female mice recognizing all pheromones as if they were from the mating male. Although protein synthesis has been shown to be essential for development of pheromone memory, the gene expression cascades critical for memory formation are not known. We investigated changes in gene expression in the AOB using oligonucleotide microarrays during mating-induced pheromone memory (MIPM) as well as bicuculline-induced pheromone memory (BIPM). We found the set of genes induced during MIPM and BIPM are largely non-overlapping and Ingenuity Pathway Analysis revealed that the signaling pathways in MIPM and BIPM also differ. The products of genes induced during MIPM are associated with synaptic function, indicating the possibility of modification at specific synapses, while those induced during BIPM appear to possess neuron-wide functions, which would be consistent with global cellular changes. Thus, these results begin to provide a mechanistic explanation for specific and non-specific memories induced by pheromones and bicuculline infusion respectively.

Time-based prospective memory impairment in patients with thalamic stroke

The role of the thalamus in memory is potentially very complex. However, most studies on the memory impairments of thalamic lesions have focused on retrospective memory, rarely on prospective memory. To explore the effect of thalamic lesions on event-based prospective memory (EBPM) and time-based prospective memory (TBPM), respectively, and to verify the hypothesis that the thalamus is involved in the prospective memory, EBPM and TBPM tasks were administered to 18 thalamic stroke patients and 18 age- and education-matched healthy controls. In the EBPM task, subjects were asked to perform an action whenever particular words were presented. In the TBPM task, subjects were asked to perform an action at certain times. Compared with the performance of healthy controls on EBPM and TBPM tasks (EBPM, 4.3 +/- 1.5; TBPM, 5.4 +/- 1.0), there was a significant difference in the performance of thalamic stroke patients in the TBPM tasks (2.4 +/- 1.6), but no difference was found in EBPM tasks (3.7 +/- 1.1). These results may indicate that the thalamus is involved in PM and particularly in TBPM.

Memory profiles in schizophrenia: categorization validity and stability

BACKGROUND

Memory profiles corresponding to nearly normal (NN), Subcortical impairment (Sub) and Cortical impairment (Cort) have been identified in schizophrenia by several investigators using cluster analytic techniques. Specific aims of the current study were to (1) perform a K means cluster analysis using Hopkins Verbal Learning Test-R scores (2) create classification rules based upon cluster distributions and expected memory profiles and to determine their concordance with cluster analysis; (3) explore differences among classified groups on demographic, neurocognitive and social cognitive domains; and (4) determine the stability of the classifications 12 months later.

METHODS

Clinical and neuropsychological assessments were obtained at intake and 12 months from 151 outpatients with schizophrenia or schizoaffective disorder from an urban community mental health center.

RESULTS

Clusters corresponded to those of the three expected subgroups. Using simple decision rules, rationally-derived groups were created and had 90% classification agreement with cluster groups. Groups did not differ on illness characteristics. Groups differed significantly in neurocognitive and social cognitive domains with NN>Cort and NN>Sub in all domains except visual/motor speed. Sub>Cort in verbal working memory. NN>Cort in social cognition. Rationally derived groupings showed fair stability at 12 month follow-up with 65% classification agreement. Specificity was good for NN (82.4%).

DISCUSSION

Results support validity of memory profiles and offer some support for their stability at 12 months. The simple rules for classification can be used by other investigators for neuroimaging and other studies. Findings support the hypothesis that verbal memory may be an important source of heterogeneity in schizophrenia.

Development of a New Delayed Memory Index for the WMS-III

This paper presents the Delayed Memory Index (DMI) as an alternative to the General Memory Index (GMI) of the Weschler Memory Scale-Third Edition (WMS-III). The WMS-III Immediate Memory Index (IMI) and the GMI are not parallel in structure, making a direct comparison between these index scores (i.e., immediate vs. delayed memory variables) difficult. The IMI is composed of the sum of scaled scores of four subtests (Logical Memory I, Verbal Paired Associates I, Faces I, and Family Pictures I) while the GMI is composed of the sum of scaled scores of five subtests (Logical Memory II, Verbal Paired Associates II, Faces II, Family Pictures II and Auditory Recognition Delayed). Inclusion of Auditory Recognition Delayed in the GMI is also problematic as it is highly skewed and limited by extreme ceiling effects (see Tulsky, Chiaravalloti, Palmer, & Chelune, 2003). To remedy these problems, we present a new index score that does not include auditory recognition, the Delayed Memory Index. Normative tables for the new Delayed Memory Index based on the inclusion of the Faces subtest, or alternatively the Visual Reproduction subtest, are presented, and initial estimates of their psychometric properties are described.

Working memory and long-term memory deficits in schizophrenia: is there a common substrate?

Patients with schizophrenia exhibit substantial deficits in both working memory (WM) and long-term memory (LTM) tasks. While these two forms of memory are generally viewed as distinct, recent evidence from healthy subjects has challenged the robustness of the double-dissociation between these two types of memory. In light of an emerging view of WM and LTM as being subserved by a largely overlapping network of brain regions, it is possible that WM and LTM deficits in patients with schizophrenia share a common neurobiological substrate. This review revisits the functional neuroimaging literature on both WM and LTM in patients with schizophrenia with these considerations in mind, and reveals a number of commonalities in research findings in both literatures. While there is a paucity of direct evidence bearing on whether patient deficits in these tasks arise from a common functional abnormality, the available literature is consistent with the hypothesis that these deficits have the same origin.

[Organization of emotional memories in autobiographical memory]

AIM

The author presents a new methodological approach to directed cued recall which point out the organization of emotional memories in autobiographical memory.

RESULTS

This approach gave opportunity to show connections between type of cues and attributes of recall memories in a group of 40 healthy persons.

CONCLUSIONS

The research proved that there exists a tendency to recall mostly positive memories in reaction to positive cues, negative memories in reaction to negative cues, while the ambivalent cues caused recollection of mostly positive feelings although with a significant number of negative remembrances. What is more, experiments indicated that respondents' reminiscences were recalled in the shortest time when the cue was positive, in the longest time when the cue was ambivalent. Moreover, the largest number of remembrances was generated in response to positive cues.

The role of the cerebellar interpositus nucleus in short and long term memory for trace eyeblink conditioning

In previous studies the cerebellar interpositus (IP) nucleus, but not the hippocampus, was shown to be necessary both for initial learning and retention and for long-term retention of the standard delay eyeblink conditioned response (CR). However, in the trace eyeblink CR procedure, the hippocampus is also necessary for initial learning and retention, but not for long-term retention. Here the authors evaluate the role of the IP nucleus in both initial learning and retention, and in long-term retention of the trace eyeblink CR, using muscimol infusion to reversibly inactivate the IP nucleus. For the short-term study, there were two subgroups, the first sequentially passed through acquisition, inactivation, and reacquisition phases, whereas the second subgroup went through inactivation, acquisition, and inactivation phases. For the long-term study, the rabbits acquired the CR and then rested for a month. Next, they were distributed into two subgroups: with or without retention training, and finally went through inactivation and reacquisition phases. The results showed that the prelearning IP nucleus inactivation prevented the acquisition of the trace CR, whereas the postlearning inactivation reversibly abolished the expression of both the short- and long-term CR.

Brain substrates of implicit and explicit memory: the importance of concurrently acquired neural signals of both memory types

A comprehensive understanding of human memory requires cognitive and neural descriptions of memory processes along with a conception of how memory processing drives behavioral responses and subjective experiences. One serious challenge to this endeavor is that an individual memory process is typically operative within a mix of other contemporaneous memory processes. This challenge is particularly disquieting in the context of implicit memory, which, unlike explicit memory, transpires without the subject necessarily being aware of memory retrieval. Neural correlates of implicit memory and neural correlates of explicit memory are often investigated in different experiments using very different memory tests and procedures. This strategy poses difficulties for elucidating the interactions between the two types of memory process that may result in explicit remembering, and for determining the extent to which certain neural processing events uniquely contribute to only one type of memory. We review recent studies that have succeeded in separately assessing neural correlates of both implicit memory and explicit memory within the same paradigm using event-related brain potentials (ERPs) and functional magnetic resonance imaging (fMRI), with an emphasis on studies from our laboratory. The strategies we describe provide a methodological framework for achieving valid assessments of memory processing, and the findings support an emerging conceptualization of the distinct neurocognitive events responsible for implicit and explicit memory.

Patterns of memory: a normative taxonomy of the Wide Range Assessment of Memory and Learning-Second Edition (WRAML-2)

Memory is arguably the most important function of cognition. When left undetected, memory impairments are linked to life long underachievement and negative social consequences. Given that the construct of memory is multidimensional, the current study examined patterns of multiple indicators associated with memory across individuals ranging in age from 5 to 85 years who had been administered the Wide Range Assessment of Memory and Learning-Second Edition (WRAML-2). Multistage cluster analysis with independent age replications was used to empirically identify normative profiles in a sample of (n = 1172) typically developing individuals. This procedure considered how various indicators of memory operate in concert by accounting for the nonlinear multivariate relationships among them. Results supported nine common (or core) profile types that satisfied all formal heuristic and statistical criteria, including complete coverage, satisfactory within-type homogeneity, between-type dissimilarity, and replicability. A summary of the defining characteristics for each profile is provided.

Enactment versus conceptual encoding: equivalent item memory but different source memory

It has been suggested that performing a physical action (enactment) is an optimally effective encoding task, due to the incorporation of motoric information in the episodic memory trace, and later retrieval of that information. The current study contrasts old/new recognition of objects after enactment to a conceptual encoding task of cost estimation. Both encoding tasks yielded high accuracy, and robust differences in brain activity as compared to new objects, but no differences between encoding tasks. These results are not supportive of the idea that encoding by enactment leads to the spontaneous retrieval of motoric information. When participants were asked to discriminate between the two classes of studied objects during a source memory task, perform-encoded objects elicited higher accuracy and different brain activity than cost-encoded objects. The extent and nature of what was retrieved from memory thus depended on its utility for the assigned memory test: object information during the old/new recognition test, but additional information about the encoding task when necessary for a source memory test. Event-related potentials (ERPs) recorded during the two memory tests showed two orthogonal effects during an early (300-800 msec) time window: a differentiation between studied and unstudied objects, and a test-type (retrieval orientation) effect that was equivalent for old and new objects. Later brain activity (800-1300 msec) differentiated perform- from cost-encoded objects, but only during the source memory test, suggesting temporally distinct phases of retrieval.

Differential effects of depressive symptoms on prospective and retrospective memory in old age

The effects of depressive symptoms on prospective and retrospective memory were examined in a population-based sample of elderly persons (n = 404). Depression was assessed using the Comprehensive Psychopathological Rating Scale and treated as a continuous variable. The variation in depressive symptoms ranged from no symptoms to presence of a clinical depression. Depressive symptoms had a negative effect on consolidation and retrieval in retrospective memory. However, the retrospective, but not the prospective, component of prospective memory was affected by depression. The findings are discussed in light of medial-temporal lobe alterations in depression.

Nonverbal deficits in explicit and implicit memory of Parkinson's disease patients

This study examined verbal and nonverbal aspects of explicit and implicit memory in a sample of 19 Parkinson's disease (PD) patients and 21 control subjects. For implicit memory evaluation, we used a Mirror Reading (MR) task employing verbal material as well as a nonverbal Serial Reaction Time (SRT) task. For explicit memory measurement we applied a word pairs task (verbal) and pairs of a Japanese ideograms task (nonverbal). The PD patients displayed impairments in the nonverbal tasks only, namely, in the SRT task and the pairs of Japanese ideograms task. No correlation between Wisconsin Card Sorting Test (WCST) scores and the results of tasks in which PD patients displayed deficits (SRT and pairs of Japanese ideograms) were discovered. Interestingly, such a correlation was found in the case of MR and words pairs tasks, which did not distinguish PD patients from control group.

What are the differences between long-term, short-term, and working memory?

In the recent literature there has been considerable confusion about the three types of memory: long-term, short-term, and working memory. This chapter strives to reduce that confusion and makes up-to-date assessments of these types of memory. Long- and short-term memory could differ in two fundamental ways, with only short-term memory demonstrating (1) temporal decay and (2) chunk capacity limits. Both properties of short-term memory are still controversial but the current literature is rather encouraging regarding the existence of both decay and capacity limits. Working memory has been conceived and defined in three different, slightly discrepant ways: as short-term memory applied to cognitive tasks, as a multi-component system that holds and manipulates information in short-term memory, and as the use of attention to manage short-term memory. Regardless of the definition, there are some measures of memory in the short term that seem routine and do not correlate well with cognitive aptitudes and other measures (those usually identified with the term "working memory") that seem more attention demanding and do correlate well with these aptitudes. The evidence is evaluated and placed within a theoretical framework depicted in Fig. 1.

Awareness, dreaming and unconscious memory formation during anaesthesia in children

Recent studies have reported an incidence of awareness in children of around 1%, while older studies reported incidences varying from 0% to 5%. Measuring awareness in children requires techniques specifically adapted to a child's cognitive development and variations in incidence may be partly explained by the measures used. The causes and consequences of awareness in children remain poorly defined, though a consistent finding is that many children do not seem distressed by their memories. There are, however, some published reports of persistent psychological symptoms after episodes of childhood awareness. Compared to explicit memory, implicit memory is more robust in young children; however there is no evidence yet for implicit memory formation during anaesthesia in children. Children less than 3 years of age do not form explicit memory, although toddlers, infants and even neonates have signs of consciousness and implicit memory formation. In these very young children the relevance of awareness remains largely unknown.

Life-long environmental enrichment differentially affects the mnemonic response to estrogen in young, middle-aged, and aged female mice

The present study was designed to examine whether life-long exposure to standard or enriched housing affects the ability of estrogen to improve spatial and object memory throughout the lifespan. Three-week-old female mice were maintained in standard or enriched housing up to and through ovariectomy and behavioral testing at 5, 17, or 22 months of age. Spatial memory was tested in the Morris water maze and object memory was tested using an object recognition task. Immediately after training each day, mice were injected intraperitoneally with vehicle or 0.2 mg/kg 17beta-estradiol. Among young females, object recognition was enhanced by estradiol alone, an effect that was reduced by enrichment. In contrast, spatial water maze performance was impaired by estradiol alone, but improved by the combination of both estradiol and enrichment. At middle-age, object recognition was enhanced by estradiol or enrichment alone, and the combination of both treatments. Spatial memory in the water maze was also improved by both treatments at middle-age, but the beneficial effects of estradiol were limited to standard-housed females. Finally, whereas enrichment in aged females significantly enhanced performance in both tasks, estradiol had no effect at this age in either task. In total, the data indicate that life-long enrichment can significantly alter the extent to which estradiol affects memory in mice throughout the lifespan. Importantly, the interaction between these treatments is highly dependent on age and type of memory tested.

Amnestic mild cognitive impairment: Difference of memory profile in subjects who converted or did not convert to Alzheimer's disease

Episodic long-term, short-term, and implicit memory were investigated in 79 elderly subjects who fulfilled criteria for the amnestic form of mild cognitive impairment (a-MCI; i.e., by having an idiopathic amnestic disorder with absence of impairment in cognitive areas other than memory and without confounding medical or psychiatric conditions) and who developed Alzheimer's disease (AD) after 2 years as well as in 111 subjects affected by a-MCI who did not develop dementia. Results document a memory profile in a-MCI subjects characterized by preserved short-term and implicit memory and extensive impairment of episodic long-term memory. In virtually all episodic memory indexes examined (learning, forgetting, recognition abilities), a-MCI subjects who converted to AD were more severely impaired than were subjects who did not become demented. This memory profile, which closely resembles that exhibited by amnestic patients with bilateral mesial-temporal lobe lesions, confirms a precocious phase in preclinical AD characterized by selective involvement of mesial-temporal areas and worsening of the memory impairment as atrophic changes progress in hippocampal structures. In this context of pervasive episodic memory impairment, tests assessing the free recall of verbal material following a delay interval demonstrated the greater sensitivity to memory deficits of a-MCI subjects who developed AD.

Frontal cortical α7 and α4β2 nicotinic acetylcholine receptors in working and reference memory

The alpha7 and alpha4beta2 nicotinic acetylcholine receptor (nAchR) subtypes have been shown to be involved in memory. It is also known that losses of frontal cortical nAchRs are correlated to declining memory function in Alzheimer's disease, but the subtype-specific role of frontal cortical nAchRs in memory has not been well characterized. Hence, we sought to understand the role of frontal cortical alpha7 and alpha4beta2 nAchR subtypes in both working and reference memory by observing the effects of subtype specific agonists and antagonists on radial arm maze performance. It was found that alpha7 nAchRs in the frontal cortex are involved in working and reference memory, while alpha4beta2 nAchRs are only involved in working memory. Throughout the study, drug treatments did not affect motor functionality in the animals. Our data thus sheds further light on the frontal cortex as an important anatomical locus for nAchR-mediated memory function in the brain, and highlights the differing role of alpha7 and alpha4beta2 nAchRs in long and short term memory.

Prospective, declarative, and nondeclarative memory in young adults with spina bifida

The consequences of congenital brain disorders for adult cognitive function are poorly understood. We studied different forms of memory in 29 young adults with spina bifida meningomyelocele (SBM), a common and severely disabling neural tube defect. Nondeclarative and semantic memory functions were intact. Working memory was intact with low maintenance and manipulation requirements, but impaired on tasks demanding high information maintenance or manipulation load. Prospective memory for intentions to be executed in the future was impaired. Immediate and delayed episodic memory were poor. Memory deficits were exacerbated by an increased number of lifetime shunt revisions, a marker for unstable hydrocephalus. Memory status was positively correlated with functional independence, an important component of quality of life.

Correlations between Regional Brain Volumes and Memory Performance in Anoxia

This study was aimed at investigating the quantitative relationship between regional brain volumes (hippocampus, amygdala, as well as cerebrum, frontal lobe, parietal lobe, temporal lobe) and performance on anterograde and retrograde memory tests in anoxic patients. We used high-resolution MRI to measure brain volumes in 13 anoxic patients. Neuropsychological testing was conducted contemporaneously with MRI. To control for age and sex, neuroanatomical volume residuals were calculated using regression equations derived from a group of 87 healthy comparison participants. We found that anoxic patients with severe amnesia had hippocampal volumes that were 36% smaller than normal, whereas patients with mild or no amnesia had normal hippocampal volumes. Regional gray matter volumes in severe amnesic anoxics were substantially smaller than expected. Performances on anterograde memory tests were significantly correlated with hippocampal and regional gray matter volume residuals. There was a significant correlation between white matter volume (but not hippocampal volume) and performance on the Visual Retention Test, a multi-dimensional test of cognitive function. There were no significant correlations between neuroanatomical measures and performance on a retrograde memory test. Our results indicate a strong quantitative relationship between performance on anterograde memory tests and hippocampal and regional gray matter volume residuals. Correlations between white matter volume residuals and performance on the VRT were found to be independent of hippocampal volume. Given the strong correlation between hippocampal volume and total gray matter volume residuals, a quantitative, normalized measure of total gray matter volume may provide a good indication of clinical outcome in anoxia.

Measurement of remote memory pre- and post-temporal lobectomy: a longitudinal case study

There is evidence that remote memory is affected by temporal lobe epilepsy (TLE) and by temporal lobectomy (TL) for the relief of epilepsy. However, remote memory is not routinely assessed when patients with epilepsy undergo neuropsychological testing either pre- or postsurgery. We present a literature review and detailed longitudinal case study of a woman (A.Z.) who had right TLE and fears about deterioration of her remote memory following right TL. Remote memory was assessed by conventional methods (remote memory questionnaire for public events) and by a novel method of seeking vividness ratings for elicited autobiographical memories with A.Z.'s partner acting as the control. A.Z.'s level of memory for remote/recent public events and her rate of forgetting were the same as her partner's, both before and after surgery. A.Z.'s vividness ratings for her own autobiographical memories were similar to her partner's ratings for his memories. Her vividness ratings for her partner's memories that involved events common to both of them were slightly lower than his. A.Z.'s rate of forgetting of her own and her partner's memories was the same as that of her partner, both before and after surgery. There are two principal conclusions. First, this assessment method of measuring remote memory is easy to use and captured the patient's clinical concerns. Second, applying the methodology in this single case suggested that right-sided unilateral TLE and TL may pose no threat to remote memory.

A link between the hippocampal and the striatal memory systems of the brain

Two major memory systems have been recognized over the years (Squire 1987): the declarative memory system, which is under the control of the hippocampus and related temporal lobe structures, and the procedural or habit memory system, which is under the control of the striatum and its connections. Most if not all learning tasks studied in animals, however, involve either the performance or the suppression of movement; this, if learned well, may be viewed as having become a habit. It is agreed that memory rules change from their first association to those that take place when the task is mastered. Does this change of rules involve a switch from one memory system to another? Here we will comment on: 1) reversal learning in the Morris water maze (MWM), in which the declarative or spatial component of a task is changed but the procedural component (to swim to safety) persists and needs to be re-linked with a different set of spatial cues; and 2) a series of observations on an inhibitory avoidance task that indicate that the brain systems involved change with further learning.

A functional magnetic resonance imaging investigation of short-term source and item memory for negative pictures

We investigated the hypothesis that arousal recruits attention to item information, thereby disrupting working memory processes that help bind items to context. Using functional magnetic resonance imaging, we compared brain activity when participants remembered negative or neutral picture-location conjunctions (source memory) versus pictures only. Behaviorally, negative trials showed disruption of short-term source, but not picture, memory; long-term picture recognition memory was better for negative than for neutral pictures. Activity in areas involved in working memory and feature integration (precentral gyrus and its intersect with superior temporal gyrus) was attenuated on negative compared with neutral source trials relative to picture-only trials. Visual processing areas (middle occipital and lingual gyri) showed greater activity for negative than for neutral trials, especially on picture-only trials.

Stability and validity of memory-based subtypes of schizophrenia

This study assessed whether verbal memory performance indexed by the California Verbal Learning Test (CVLT) can organize and reduce the heterogeneity of schizophrenia. The temporal stability, cognitive and clinical validity of: (a) a putatively cortical-subcortical-normative typology derived from dementia patients' scores on the CVLT and (b) a memory performance dichotomy based on a psychometric criterion and 1 CVLT summary score were evaluated. These memory subtypes were examined in 102 schizophrenia patients, 55 of whom were assessed again 3 years later. The results indicate that both methods yield potentially valuable illness distinctions on a cross-sectional basis, but fail to show truly trait-like properties. Furthermore, the evidence favors the validity of a parsimonious dichotomy over a more complex dementia-based typology.

fMRI environment can impair memory performance in young and elderly adults

The influence of the fMRI (functional magnetic resonance imaging) scanning environment on working memory and long-term memory performance was investigated. We predicted that performance would be impaired on memory tasks in the distracting fMRI environment relative to laboratory performance. Results indicated that both young and old adults showed performance decrements in the scanning environment compared to the laboratory for a long-term memory task, but not for a passive working memory task, consistent with the idea that divided attention costs occur for more difficult tasks. In addition, elderly adults were disproportionately impaired by the scanning environment on the long-term memory task, congruent with the finding that divided attention costs at encoding are larger for older than younger adults. The findings suggest that performance may be changed by the scanning environment and that, in some circumstances, the fMRI environment may have a disproportionate effect on cognitive performance of older adults.

Chronic nicotine improves working and reference memory performance and reduces hippocampal NGF in aged female rats

The cholinergic system is involved in cognition and several forms of dementia, including Alzheimer's disease, and nicotine administration has been shown to improve cognitive performance in both humans and rodents. While experiments with humans have shown that nicotine improves the ability to handle an increasing working memory load, little work has been done in animal models evaluating nicotine effects on performance as working memory load increases. In this report, we demonstrate that in aged rats nicotine improved the ability to handle an increasing working memory load as well as enhanced performance on the reference memory component of the water radial arm maze task. The dose required to exert these effects (0.3mg/kg/day) was much lower than doses shown to be effective in young rats and appears to be a lower maintenance dose than is seen in light to moderate smokers. In addition, our study reports a nicotine-induced reduction in nerve growth factor (NGF) protein levels in the hippocampus of the aged rat. The effects of nicotine on hippocampal NGF levels are discussed as a potential mechanism of nicotine-induced improvements in working and reference memory.

Dorsal hippocampal α7 and α4β2 nicotinic receptors and memory

Nicotinic receptor systems have been shown to be important for working memory. In general, nicotinic agonists have been shown to improve memory, and nicotinic antagonists impair it. All of the neuronal substrates for nicotinic involvement in memory still remain to be discovered. The amygdala and ventral hippocampus have both been found to be important for nicotinic involvement in memory function. Local infusion of the nicotinic antagonist methyllycaconitine (MLA) to block alpha7 nicotinic receptors and dihydro-beta-erythrodine (DHbetaE) to block alpha4beta2 nicotinic receptors into the basolateral amygdala and the ventral hippocampus have been found to impair working memory function, with no additive effects being observed. The current project assessed the roles of alpha7 and alpha4beta2 nicotinic receptors in the dorsal hippocampus for memory function. Adult female Sprague-Dawley rats were trained on the 16-arm radial maze. The rats (n = 10) had bilateral cannulae implanted into the dorsal hippocampus. The rats were given acute infusions of DHbetaE (0, 1.69, 3.38, and 6.75 microg/side) and MLA (6.75 microg/side) alone and in combination in a repeated measures counter-balanced design. DHbetaE and MLA infusion into the dorsal hippocampus significantly increased working memory errors. However, when the two drugs were given in combination, an attenuated effect was seen. No significant effects of MLA or DHbetaE were seen with reference memory errors or response latency. These results confirm the importance of alpha4beta2 and alpha7 nicotinic acetylcholine receptors in the dorsal hippocampus for appetitively-motivated spatial cognitive function.

Stress facilitates consolidation of verbal memory for a film but does not affect retrieval

The effect of psychosocial stress on distinct memory processes was investigated in 157 college students using a brief film, which enabled comparison of verbal and visual memory by using a single complex stimulus. Participants were stressed either following stimuli presentation (consolidation) or before testing 48 hr later (retrieval) and were compared with no-stress controls. Salivary cortisol was measured before and 20 min after stress. The consolidation group significantly outperformed controls on total and verbal film scores. Stress did not impair retrieval relative to controls. Exploratory analyses revealed a significant correlation between cortisol and verbal scores across all groups (r = .18). Results provide the first evidence of a facilitative effect of a stressor on verbal memory, but failed to replicate retrieval findings.

Growth points in research on memory and hippocampus

We present an overview of two of our on-going projects relating processes in the hippocampus to memory. We are trying to understand why retrograde amnesia occurs after damage to the hippocampus. Our experiments establish the generality of several new retrograde amnesia phenomena that are at odds with the consensus view of the role of the hippocampus in memory. We show in many memory tasks that complete damage to the hippocampus produces retrograde amnesia that is equivalent for recent and remote memories. Retrograde amnesia affects a much wider range of memory tasks than anterograde amnesia. Normal hippocampal processes can interfere with retention of a long-term memory stored outside the hippocampus. We conclude that the hippocampus competes with nonhippocampal systems during memory encoding and retrieval. Finally, we outline a project to understand and manipulate adult hippocampal neurogenesis in order to repair damaged hippocampal circuitry to recover lost cognitive functions.

Doubts about double dissociations between short- and long-term memory

Historically, psychologists and neuroscientists have distinguished between processes supporting memory for events across retention delays of several seconds (short-term memory, STM), and those supporting memory for events across longer retention delays of minutes or more (long-term memory, LTM). Dissociations reported in some neuropsychological studies have contributed to a popular view that there must be neurally distinct memory stores that differentially support STM and LTM. In this article, we review evidence from recent studies regarding dissociations between STM and LTM. We suggest that the evidence reveals problems with claims of selective STM or LTM impairments, which in turn questions whether theories of memory need to propose neurally distinct stores for short- and long-term retention. We consider alternative ways to explain the neural mechanisms of memory across different retention intervals.

Memory interference in multiple sclerosis

To explore verbal memory impairments associated with multiple sclerosis (MS), we compared proactive and retroactive interference effects on the California Verbal Learning Test (CVLT; Delis et al., 1987) in a sample of 83 community-residing individuals with MS and 80 healthy participants. Individuals with MS demonstrated normal accumulation of proactive interference (PI), but attenuated release from PI relative to healthy individuals. Furthermore, accumulation of retroactive interference (RI) at short-delay free recall (SDFR) was intensified for those with MS as compared to healthy participants. Interestingly, accumulation of RI predicted long-term memory (LTM) only for participants with MS. These findings suggest that individuals with MS may experience particular difficulty when required to use semantic properties of information flexibly to facilitate verbal LTM.

Early Assessment of Dementia: The Contribution of Different Memory Components

A broad memory test battery (reflecting explicit and implicit memory functioning) was administered to a heterogeneous sample of initially nondemented, community-dwelling elderly subjects. To examine the profile of preclinical dementia, subjects were tested twice: At baseline, all subjects were nondemented according to Diagnostic and Statistical Manual of Mental Disorders (4th ed.; American Psychiatric Association, 1994) criteria; 2 years later, a subgroup had developed dementia. Performance of the preclinically demented subjects was best characterized, relative to that of cognitively impaired subjects who did not develop dementia 2 years later, by an inability to benefit at recall from semantic relations and by absent repetition priming effects. The authors conclude that in addition to testing episodic memory functioning, it is important to be aware of semantic and implicit memory deficits in the early assessment of dementia.

Category learning and multiple memory systems

Categorization is a vitally important skill that people use every day. Early theories of category learning assumed a single learning system, but recent evidence suggests that human category learning may depend on many of the major memory systems that have been hypothesized by memory researchers. As different memory systems flourish under different conditions, an understanding of how categorization uses available memory systems will improve our understanding of a basic human skill, lead to better insights into the cognitive changes that result from a variety of neurological disorders, and suggest improvements in training procedures for complex categorization tasks.

Amygdala damage impairs emotional memory for gist but not details of complex stimuli

Neurobiological studies demonstrate the amygdala's role in emotional memory, and psychological studies suggest a particular pattern: enhanced memory for the gist but not the details of complex stimuli. We hypothesized that these two findings are related. Whereas normal (n = 52) and brain-damaged (n = 22) controls showed the expected enhancement of gist memory when the encoding context was emotional, persons with unilateral damage to the medial temporal lobe including the amygdala (n = 16) did not show this pattern. Furthermore, amygdala volume showed a significant positive correlation with gist memory but not with overall memory. A further study in four subjects with selective medial temporal damage sparing the amygdala, and one with selective damage confined to the amygdala, confirmed the specificity of this effect to the amygdala. The data support a model whereby the amygdala focuses processing resources on gist, possibly accounting for features of traumatic memories and eyewitness testimony in real life.

Memory processes in classical conditioning

Classical conditioning provides a rich and powerful method for studying basic learning, memory, and emotion processes in animals. However, it is important to recognize that an animal's performance in a conditioning experiment provides only an indirect indication of what it has learned. Various remembering and forgetting processes, in addition to other psychological processes, may intervene and complicate what investigators can infer about learning from performance. This article reviews the role of context, interference, and retrieval in a number of classical conditioning phenomena (e.g. extinction), and provides an overview of how long-term and short-term memory processes influence behavior as it is studied in classical conditioning.

An analysis of independence and interactions of brain substrates that subserve multiple attributes, memory systems, and underlying processes

It is proposed that memory is organized into event-based, knowledge-based, and rule-based memory systems. Furthermore, each system is composed of the same set of multiple attributes and characterized by a set of process oriented operating characteristics that are mapped onto multiple neural regions and interconnected neural circuits. Based on this theoretical model of memory, it is possible to investigate the independence and interaction among brain regions between any two systems for any of the proposed attributes or processes. This applies also to the investigation of independence and interactions between any two attributes within a system and between processes associated with a system for any of the proposed attributes. In this article, research evidence is presented to suggest that there are both dissociations and interactions between the hippocampus and caudate nucleus in mediating spatial and response attributes within the event-based memory system, between the hippocampus and the parietal cortex in subserving the spatial attribute within the event-based and knowledge-based memory systems, and between the hippocampus and the prefrontal cortex in subserving the spatial attribute within the event-based and rule-based memory systems.

The use of acute ethanol administration as a tool to investigate multiple memory systems

The discovery of multiple memory systems supported by discrete brain regions has been one of the most important advances in behavioral neuroscience. A wealth of studies have investigated the role of the hippocampus and related structures in supporting various types of memory classifications. While the exact classification that best describes hippocampal function is often debated, a specific subset of cognitive function that is focused on the use of spatial information to form hippocampal cognitive maps has received extensive investigation. These studies frequently employ a variety of experimental manipulations including brain lesions, temporary neural blockade due to cooling or discrete injections of specific drugs. While these studies have provided important insights into the function of the hippocampus, they are limited due to the invasive nature of the manipulation. Ethanol is a drug that is easily administered in a non-invasive fashion, is rapidly absorbed and produces effects only in specific brain regions. The hippocampus is one brain region affected by acute ethanol administration. The following review summarizes research from the last 20 years investigating the effects of acute ethanol administration on one specific type of hippocampal cognitive function, namely spatial memory. It is proposed that among its many effects, one specific action of acute ethanol administration is to produce similar cognitive and neurophysiological effects as lesions of the hippocampus. Based on these similarities and the ease of its use, it is concluded that acute ethanol administration is a valuable tool in studying hippocampal function and multiple memory systems.

Learning-induced activation of transcription factors among multiple memory systems

Experimental evidence for multiple memory systems grew initially from reports that integrity of the medial temporal lobes is necessary for some, but not all, types of memory formation. A primary inference from many studies of multiple memory systems is that they operate independently during encoding, storage, and retrieval of information. An accumulation of recent evidence, however, suggests that multiple memory systems may interact under some conditions. At the cellular level of analysis, it is accepted widely that protein synthesis is necessary for the formation of long-term memory and recent efforts have focused on the mechanisms by which learning-induced gene transcription and translation are regulated. The present review examines learning-induced activation of transcription factors among multiple memory systems. The results indicate that studies of transcriptional regulation, in conjunction with other experimental approaches, can provide complementary lines of evidence to further understanding of the extent to which multiple memory systems are independent or interactive.

Memory systems of the brain: a brief history and current perspective

The idea that memory is composed of distinct systems has a long history but became a topic of experimental inquiry only after the middle of the 20th century. Beginning about 1980, evidence from normal subjects, amnesic patients, and experimental animals converged on the view that a fundamental distinction could be drawn between a kind of memory that is accessible to conscious recollection and another kind that is not. Subsequent work shifted thinking beyond dichotomies to a view, grounded in biology, that memory is composed of multiple separate systems supported, for example, by the hippocampus and related structures, the amygdala, the neostriatum, and the cerebellum. This article traces the development of these ideas and provides a current perspective on how these brain systems operate to support behavior.

Implicit and Explicit Memory in Children With Congenital and Acquired Brain Disorder

Implicit and explicit memory were examined in 8- to 15-year-old children with myelomeningocele and shunted hydrocephalus, severe traumatic brain injuries, or orthopedic injuries. Each group included between 22 and 29 children. Children completed a fragmented picture identification task to assess perceptual priming and a semantic decision-making task to assess conceptual priming. Each task also assessed procedural learning as well as explicit recall and recognition. All 3 groups showed significant perceptual and semantic priming of similar magnitude. In contrast, both brain-disordered groups displayed poorer explicit memory than did the comparison group. No group showed significant procedural learning on either task. Age and IQ were stronger predictors of explicit recall than of implicit memory. The findings indicate that implicit memory is relatively intact in many children with congenital and acquired brain disorders, despite deficits in explicit memory, and support the existence of separate memory systems in children.

Tyrosine prevents effects of hyperthermia on behavior and increases norepinephrine

Tyrosine (TYR) is the precursor of the catecholamine (CA) neurotransmitters, dopamine (DA) and norepinephrine (NE). Catecholamines, especially NE, participate in the response of the brain to acute stress. When animals are acutely stressed, NE neurons become more active and tyrosine availability may be rate-limiting. Tyrosine administration, before exposure to physical and/or environmental stressors including cold, reduces the adverse behavioral, physiological and neurochemical consequences of the exposure. In this study, the effects of tyrosine (400 mg/kg) were examined on rats exposed to heat stress, for which its effects have not been examined. Coping behavior and memory were assessed using the Porsolt swim test and the Morris water maze. Release of hippocampal NE and DA was assessed with in vivo microdialysis. In vehicle-treated animals, heat impaired coping and memory, and increased release of NE, but not DA. In heated animals receiving tyrosine, coping was not impaired and NE release was sustained, thus demonstrating tyrosine protects against the adverse effects of heat, and suggesting these effects result from increased central NE release. This study indicates the effects of tyrosine generalize across dissimilar stressors and that tyrosine administration may mitigate the adverse behavioral effects of heat and other stressors on humans. In addition, it demonstrates that moderate heat stress impairs coping behavior, as well as working and reference memory.