Spatial and temporal memory in 20 to 60 year olds

Effect of androgen receptor blockade on spatial memory in young and aged male rats in the Barnes maze

Spatial memory declines with age, and this decline is associated with decreased testosterone levels. However, the specific role of the androgen receptor in spatial memory performance in both young and aged rats remains largely unexplored. Our study aimed to investigate the effects of chronic androgen receptor blockade on spatial memory performance in young and aged male rats. Young (3 months old) and aged (21 months old) Wistar rats were assigned to one of three experimental groups: control, vehicle-, or flutamide-treated (10 mg/kg SC for 14 days). Spatial memory was evaluated using the Barnes maze (Days 8-14 of flutamide administration). The phases of spatial memory acquisition (4 daily trials/4 days) and retention (1 trial/day, 3 days after acquisition) were evaluated. The results indicated that older animals took longer to find the goal, traveled greater distances, and moved more slowly than their younger counterparts in the Barnes maze, regardless of treatment. During the acquisition phase, flutamide administration delayed learning in both young and aged animals. Specifically, flutamide-treated animals exhibited delayed learning during the assessment of overnight forgetting (trial 1 on each day of the acquisition phase). During the retention phase, an age-related effect was observed in the flutamide-treated groups. These findings suggest that androgen receptor blockade induces cognitive deficits in both young and aged male rats, supporting the modulatory role of endogenous androgens in memory function.

Event-related theta and gamma band oscillatory dynamics during visuo-spatial sequence memory in younger and older adults

Visuo-spatial working memory (VSWM) for sequences is thought to be crucial for daily behaviors. Decades of research indicate that oscillations in the gamma and theta bands play important functional roles in the support of visuo-spatial working memory, but the vast majority of that research emphasizes measures of neural activity during memory retention. The primary aims of the present study were (1) to determine whether oscillatory dynamics in the Theta and Gamma ranges would reflect item-level sequence encoding during a computerized spatial span task, (2) to determine whether item-level sequence recall is also related to these neural oscillations, and (3) to determine the nature of potential changes to these processes in healthy cognitive aging. Results indicate that VSWM sequence encoding is related to later (∼700 ms) gamma band oscillatory dynamics and may be preserved in healthy older adults; high gamma power over midline frontal and posterior sites increased monotonically as items were added to the spatial sequence in both age groups. Item-level oscillatory dynamics during the recall of VSWM sequences were related only to theta-gamma phase amplitude coupling (PAC), which increased monotonically with serial position in both age groups. Results suggest that, despite a general decrease in frontal theta power during VSWM sequence recall in older adults, gamma band dynamics during encoding and theta-gamma PAC during retrieval play unique roles in VSWM and that the processes they reflect may be spared in healthy aging.

A Structure-Function Substrate of Memory for Spatial Configurations in Medial and Lateral Temporal Cortices

Prior research has shown a role of the medial temporal lobe, particularly the hippocampal-parahippocampal complex, in spatial cognition. Here, we developed a new paradigm, the conformational shift spatial task (CSST), which examines the ability to encode and retrieve spatial relations between unrelated items. This task is short, uses symbolic cues, incorporates two difficulty levels, and can be administered inside the scanner. A cohort of 48 healthy young adults underwent the CSST, together with a set of behavioral measures and multimodal magnetic resonance imaging (MRI). Inter-individual differences in CSST performance correlated with scores on an established spatial memory paradigm, but neither with episodic memory nor mnemonic discrimination, supporting specificity. Analyzing high-resolution structural MRI data, individuals with better spatial memory showed thicker medial and lateral temporal cortices. Functional relevance of these findings was supported by task-based functional MRI analysis in the same participants and ad hoc meta-analysis. Exploratory resting-state functional MRI analyses centered on clusters of morphological effects revealed additional modulation of intrinsic network integration, particularly between lateral and medial temporal structures. Our work presents a novel spatial memory paradigm and supports an integrated structure-function substrate in the human temporal lobe. Task paradigms are programmed in python and made open access.

Impaired spatial pattern separation performance in temporal lobe epilepsy is associated with visuospatial memory deficits and hippocampal volume loss

Individuals with chronic temporal lobe epilepsy (TLE) experience episodic memory deficits that may be progressive in nature. These memory decrements have been shown to increase with the extent of hippocampal damage, a hallmark feature of TLE. Pattern separation, a neural computational mechanism thought to play a role in episodic memory formation, has been shown to be negatively affected by aging and in individuals with known hippocampal dysfunction. Despite the link between poor pattern separation performance and episodic memory deficits, behavioral pattern separation has not been examined in patients with TLE. We examined pattern separation performance in a group of 22 patients with medically-refractory TLE and 20 healthy adults, using a task hypothesized to measure spatial pattern separation with graded levels of spatial interference. We found that individuals with TLE showed less efficient spatial pattern separation performance relative to healthy adults. Poorer spatial pattern separation performance in TLE was associated with poorer visuospatial memory, but only under high interference conditions. In addition, left hippocampal atrophy was associated with poor performance in the high interference condition in TLE. These data suggest that episodic memory impairments in patients with chronic, refractory TLE may be partially due to less efficient pattern separation, which likely reflects their underlying hippocampal dysfunction.

Loss of Catecholaminergic Neuromodulation of Persistent Forms of Hippocampal Synaptic Plasticity with Increasing Age

Neuromodulation by means of the catecholaminergic system is a key component of motivation-driven learning and behaviorally modulated hippocampal synaptic plasticity. In particular, dopamine acting on D1/D5 receptors and noradrenaline acting on beta-adrenergic receptors exert a very potent regulation of forms of hippocampal synaptic plasticity that last for very long-periods of time (>24 h), and occur in conjunction with novel spatial learning. Antagonism of these receptors not only prevents long-term potentiation (LTP) and long-term depression (LTD), but prevents the memory of the spatial event that, under normal circumstances, leads to the perpetuation of these plasticity forms. Spatial learning behavior that normally comes easily to rats, such as object-place learning and spatial reference learning, becomes increasingly impaired with aging. Middle-aged animals display aging-related deficits of specific, but not all, components of spatial learning, and one possibility is that this initial manifestation of decrements in learning ability that become apparent in middle-age relate to changes in motivation, attention and/or the regulation by neuromodulatory systems of these behavioral states. Here, we compared the regulation by dopaminergic D1/D5 and beta-adrenergic receptors of persistent LTP in young (2-4 month old) and middle-aged (8-14 month old) rats. We observed in young rats, that weak potentiation that typically lasts for ca. 2 h could be strengthened into persistent (>24 h) LTP by pharmacological activation of either D1/D5 or beta-adrenergic receptors. By contrast, no such facilitation occurred in middle-aged rats. This difference was not related to an ostensible learning deficit: a facilitation of weak potentiation into LTP by spatial learning was possible both in young and middle-aged rats. It was also not directly linked to deficits in LTP: strong afferent stimulation resulted in equivalent LTP in both age groups. We postulate that this change in catecholaminergic control of synaptic plasticity that emerges with aging, does not relate to a learning deficit per se, rather it derives from an increase in behavioral thresholds for novelty and motivation that emerge with increasing age that impact, in turn, on learning efficacy.

Changes in the modulation of brain activity during context encoding vs. context retrieval across the adult lifespan

Age-related deficits in context memory may arise from neural changes underlying both encoding and retrieval of context information. Although age-related functional changes in the brain regions supporting context memory begin at midlife, little is known about the functional changes with age that support context memory encoding and retrieval across the adult lifespan. We investigated how age-related functional changes support context memory across the adult lifespan by assessing linear changes with age during successful context encoding and retrieval. Using functional magnetic resonance imaging (fMRI), we compared young, middle-aged and older adults during both encoding and retrieval of spatial and temporal details of faces. Multivariate behavioral partial least squares (B-PLS) analysis of fMRI data identified a pattern of whole-brain activity that correlated with a linear age term and a pattern of whole-brain activity that was associated with an age-by-memory phase (encoding vs. retrieval) interaction. Further investigation of this latter effect identified three main findings: 1) reduced phase-related modulation in bilateral fusiform gyrus, left superior/anterior frontal gyrus and right inferior frontal gyrus that started at midlife and continued to older age, 2) reduced phase-related modulation in bilateral inferior parietal lobule that occurred only in older age, and 3) changes in phase-related modulation in older but not younger adults in left middle frontal gyrus and bilateral parahippocampal gyrus that was indicative of age-related over-recruitment. We conclude that age-related reductions in context memory arise in midlife and are related to changes in perceptual recollection and changes in fronto-parietal retrieval monitoring.

Cultural background shapes spatial reference frame proclivity

Spatial navigation is an essential human skill that is influenced by several factors. The present study investigates how gender, age, and cultural background account for differences in reference frame proclivity and performance in a virtual navigation task. Using an online navigation study, we recorded reaction times, error rates (confusion of turning axis), and reference frame proclivity (egocentric vs. allocentric reference frame) of 1823 participants. Reaction times significantly varied with gender and age, but were only marginally influenced by the cultural background of participants. Error rates were in line with these results and exhibited a significant influence of gender and culture, but not age. Participants’ cultural background significantly influenced reference frame selection; the majority of North-Americans preferred an allocentric strategy, while Latin-Americans preferred an egocentric navigation strategy. European and Asian groups were in between these two extremes. Neither the factor of age nor the factor of gender had a direct impact on participants’ navigation strategies. The strong effects of cultural background on navigation strategies without the influence of gender or age underlines the importance of socialized spatial cognitive processes and argues for socio-economic analysis in studies investigating human navigation.

Differences in temporal order memory among young, middle-aged, and older adults may depend on the level of interference

Age-related changes in temporal order memory have been well documented in older adults; however, little is known about this ability during middle age. We tested healthy young, middle-aged, and older adults on a previously published visuospatial temporal order memory test involving high and low interference conditions. When interference was low, young and middle-aged adults did not differ, but both groups significantly outperformed older adults. However, when interference was high, significant differences were found among all three age groups. The data provide evidence that temporal order memory may begin to decline in middle age, particularly when temporal interference is high.

Temporal discrimination deficits as a function of lag interference in older adults

A vital component of episodic memory is the ability to determine the temporal order of remembered events. Although it has been demonstrated that the hippocampus plays a crucial role in this ability, the details of its contributions are not yet fully understood. One proposed contribution of the hippocampus is the reduction of mnemonic interference through pattern separation. Prior studies have used behavioral paradigms designed to assess this function in the temporal domain by evaluating the ability to determine the order of remembered events as a function of proximity in time. Results from these paradigms in older adults (OA) have been mixed, possibly due to limitations in controlling elapsed time and narrow range of temporal lags. Here, we introduce a novel behavioral paradigm designed to overcome these limitations. We report that OAs are impaired relative to younger adults at moderate and high temporal lags but not at low lags (where performance approached floor). We evaluated OAs' ability to benefit from primacy (enhanced order judgment on the first few items of any given sequence) and found two distinct subgroups: one group was on par with young adults [aged-unimpaired (AU)] and the other group was two standard deviations below the mean of young adults [aged-impaired (AI)]. Temporal discrimination performance in AU adults was consistent with a pattern separation deficit, while performance in AI adults was consistent with a generalized temporal processing deficit. We propose that the task introduced is a sensitive marker for episodic memory deficits with age, and may have diagnostic value for early detection of age-related pathology.

Early age-dependent impairments of context-dependent extinction learning, object recognition, and object-place learning occur in rats

The hippocampus is vulnerable to age-dependent memory decline. Multiple forms of memory depend on adequate hippocampal function. Extinction learning comprises active inhibition of no longer relevant learned information concurrent with suppression of a previously learned reaction. It is highly dependent on context, and evidence exists that it requires hippocampal activation. In this study, we addressed whether context-based extinction as well as hippocampus-dependent tasks, such as object recognition and object-place recognition, are equally affected by moderate aging. Young (7-8 week old) and older (7-8 month old) Wistar rats were used. For the extinction study, animals learned that a particular floor context indicated that they should turn into one specific arm (e.g., left) to receive a food reward. On the day after reaching the learning criterion of 80% correct choices, the floor context was changed, no reward was given and animals were expected to extinguish the learned response. Both, young and older rats managed this first extinction trial in the new context with older rats showing a faster extinction performance. One day later, animals were returned to the T-maze with the original floor context and renewal effects were assessed. In this case, only young but not older rats showed the expected renewal effect (lower extinction ratio as compared to the day before). To assess general memory abilities, animals were tested in the standard object recognition and object-place memory tasks. Evaluations were made at 5 min, 1 h and 7 day intervals. Object recognition memory was poor at short-term and intermediate time-points in older but not young rats. Object-place memory performance was unaffected at 5 min, but impaired at 1 h in older but not young rats. Both groups were impaired at 7 days. These findings support that not only aspects of general memory, but also context-dependent extinction learning, are affected by moderate aging. This may reflect less flexibility in revising hard-wired knowledge or reduced adaptability to new learning challenges.

Memory in aged mice is rescued by enhanced expression of the GluN2B subunit of the NMDA receptor

The GluN2B subunit of the N-methyl-d-aspartate (NMDA) receptor shows age-related declines in expression across the frontal cortex and hippocampus. This decline is strongly correlated to age-related memory declines. This study was designed to determine if increasing GluN2B subunit expression in the frontal lobe or hippocampus would improve memory in aged mice. Mice were injected bilaterally with either the GluN2B vector, containing cDNA specific for the GluN2B subunit and enhanced green fluorescent protein (eGFP); a control vector or vehicle. Spatial memory, cognitive flexibility, and associative memory were assessed using the Morris water maze. Aged mice, with increased GluN2B subunit expression, exhibited improved long-term spatial memory, comparable to young mice. However, memory was rescued on different days in the Morris water maze; early for hippocampal GluN2B subunit enrichment and later for the frontal lobe. A higher concentration of the GluN2B antagonist, Ro 25-6981, was required to impair long-term spatial memory in aged mice with enhanced GluN2B expression, as compared to aged controls, suggesting there was an increase in the number of GluN2B-containing NMDA receptors. In addition, hippocampal slices from aged mice with increased GluN2B subunit expression exhibited enhanced NMDA receptor-mediated excitatory post-synaptic potentials (EPSP). Treatment with Ro 25-6981 showed that a greater proportion of the NMDA receptor-mediated EPSP was due to the GluN2B subunit in these animals, as compared to aged controls. These results suggest that increasing the production of the GluN2B subunit in aged animals enhances memory and synaptic transmission. Therapies that enhance GluN2B subunit expression within the aged brain may be useful for ameliorating age-related memory declines.

Age Differences in Recall and Information Processing in Verbal and Spatial Learning

Les différences selon l'âge dans les apprentissages verbaux et spatiaux et le traitement des informations obtenues ont été testées à partir de deux exercices d'apprentissage portant respectivement sur des listes verbales de mots et sur des listes visuo-spatiales. Les réminiscences ont été évaluées au cours de cinq essais d'apprentissage et les mêmes instruments de traitement de l'information et de stratégie organisationnelle ont été utilisés à partir des deux types d'exercice ci-haut mentionnés. Des sujets normaux, divisés en trois groupes d'âge de 24 sujets chacun, ont été comparés sur la base de ces instruments. Tant les essais que les types de tâches (verbales vs spatiales) ont permis d'observer des différences significatives selon l'âge et ce, pour la moyenne de toutes les réminiscences. Par rapport aux apprentissages verbaux et aux apprentissages spatiaux, l'âge n'a pas présenté de différences significatives. De plus, il n'y a pas eu de modèles différents de réminiscences selon les groupes d'âge au cours des essais d'apprentissage. Par contre l'âge a été relié à des types de mesures dites d'agglomération, mesures destinées à évaluer l'organisation de l'information selon des catégories sémantiques verbales ou visuelles. Au cours d'essais antérieurs d'apprentissage et sur des sujets plus jeunes, on avait abouti à de plus hauts niveaux d'agglomération. Les instruments verbaux et spatiaux d'agglomération ont donné les mêmes résultats. En ce qui concerne l'ordre, dans le temps, de présentation de l'information, l'âge n'avait rien à voir avec les différences d'organisation des essais. Les résultats présentent le même type de différences reliées à l'âge, dans les listes d'apprentissages verbales ou spatiales. Cela nous prouve que l'apprentissage verbal aussi bien que l'apprentissage spatial repose sur un traitement de l'information requérant beaucoup d'efforts.

Assessment of spatial memory in mice

Improvements in health care have greatly increased life span in the United States. The focus is now shifting from physical well-being to improvement in mental well-being or maintenance of cognitive function in old age. It is known that elderly people suffer from cognitive impairment, even without neurodegeneration, as a part of 'normal aging'. This 'age-associated memory impairment' (AAMI), can have a devastating impact on the social and economic life of an individual as well as the society. Scientists have been experimenting to find methods to prevent the memory loss associated with aging. The major factor involved in these experiments is the use of animal models to assess hippocampal-based spatial memory. This review describes the different types of memory including hippocampal-based memory that is vulnerable to aging. A detailed overview of various behavioral paradigms used to assess spatial memory including the T-maze, radial maze, Morris water maze, Barnes maze and others is presented. The review also describes the molecular basis of memory in hippocampus called as 'long-term potentiation'. The advantages and limitations of the behavioral models in assessing memory and the link to the long-term potentiation are discussed. This review should assist investigators in choosing suitable methods to assess spatial memory in mice.

Effect of age on proliferation-regulating factors in human adult neurogenic regions

Neurogenesis, the birth of new neurons, continues throughout adulthood in the human subventricular zone (SVZ) and hippocampus. It is not known how levels of putative proliferation-regulating factors change with age in human adult neurogenic areas. The current project employed ELISAs to investigate changes in levels of putative proliferation-regulating factors in the healthy human SVZ and dentate gyrus throughout the adult lifespan (18-104 years). Levels of brain-derived neurotrophic factor, basic fibroblast growth factor and interleukin (IL)-1β were significantly higher in the hippocampus than in the SVZ and levels of glial-derived neurotrophic factor and transforming growth factor-α were significantly higher in the SVZ (p < 0.005), suggesting that factors with predominant influences on neurogenesis differ between the two human adult neurogenic areas. Hippocampal levels of transforming growth factor-β1 strongly increased with age (n = 9, p < 0.01), whereas hippocampal and SVZ levels of brain-derived neurotrophic factor, epidermal growth factor, basic fibroblast growth factor, glial-derived neurotrophic factor, heparin-binding epidermal growth factor, insulin-like growth factor-1, IL-1β, IL-6 and transforming growth factor-α did not change significantly with age in the SVZ or hippocampus. These findings suggest regulation of the adult neurogenic environment in the human brain may differ over time from that in other species.

AGING, CONTEXT MEMORY AND BINDING: A COMPARISON OF “WHAT, WHERE AND WHEN” IN YOUNG AND OLDER ADULTS

There is evidence that age-related memory decline does not effect all types of episodic information to an equal extent, but that especially contextual memory and the integration of multiple features in memory deteriorate. The current study investigates contextual memory in a group of healthy young (N = 40) and older (N = 40) adults without dementia. All participants performed a computerized memory task assessing target memory (objects only), contextual memory (positions only) and memory for the combinations of two features (object, space, temporal order), that is, binding of target-context or context-context features. The results showed age-related decline on all task conditions. Furthermore, the performance on conditions requiring the binding of target and context features was affected to a greater extent in older adults compared to younger adults. These findings support the notion that a decline in contextual memory and binding might underlie poorer episodic memory in older participants.

Age-related changes in imitating sequences of observed movements

Three experiments investigated the size and sources of age-related changes in visual imitation. In Experiment 1, young and older adults viewed sequences of quasi-random movements and then reproduced from memory what they had seen. As expected, older adults made more errors in imitation than their younger counterparts. However, older adults seemed to supplement their memory by exploiting an abstracted representation (gist) of a sequence. Experiments 2 and 3 apportioned the observed age-related changes in imitation performance among several possible causes. Experiment 2 showed that changes in precision of visual perception and motor control together accounted for only a small fraction of age-related changes in imitation quality; Experiment 3 showed that the bulk of the age-related changes arose from the older participants' reduced ability to accommodate for increases in memory load, likely caused by diminished ability to encode or retain detailed information about movement sequences. Guided by these results, strategies are proposed for enhancing older adults' imitation learning.

Cognition and Elderly People

An overview of the experimental literature on ageing and cognition in the areas of sensation and perception, attention and performance, learning and memory, and intelligence and problem solving is provided. The review indicates definite deficits in most functions, and therefore provides a basis for understanding the origin of the stereotypes of the elderly as senile, obsolete, and useless. However, when viewed in a broad, integrated perspective, there seems to be grounds for a less pessimistic outlook than most people have. The most positive findings are some recent ones in the area of memory, which show that the elderly are able to make use of the knowledge they have accumulated over a lifetime to perform some tasks as good as or better than younger adults. Some researchers have begun to lay plans for the development of intervention programmes for the elderly, and we suggest some areas which may be profitable for further development. There are, however, some difficult motivational issues that need to be dealt with. It seems that many elderly persons claim to be functioning to their own satisfaction, from a cognitive perspective.

Upregulation of calcium/calmodulin-dependent protein kinase IV improves memory formation and rescues memory loss with aging

Previous studies have suggested that calcium/calmodulin-dependent protein kinase IV (CaMKIV) functions as a positive regulator for memory formation and that age-related memory deficits are the result of dysfunctional signaling pathways mediated by cAMP response element-binding protein (CREB), the downstream transcription factor of CaMKIV. Little is known, however, about the effects of increased CaMKIV levels on the ability to form memory in adult and aged stages. We generated a transgenic mouse overexpressing CaMKIV in the forebrain and showed that the upregulation of CaMKIV led to an increase in learning-induced CREB activity, increased learning-related hippocampal potentiation, and enhanced consolidation of contextual fear and social memories. Importantly, we also observed reduced hippocampal CaMKIV expression with aging and a correlation between CaMKIV expression level and memory performance in aged mice. Genetic overexpression of CaMKIV was able to rescue associated memory deficits in aged mice. Our findings suggest that the level of CaMKIV expression correlates positively with the ability to form long-term memory and implicate the decline of CaMKIV signaling mechanisms in age-related memory deficits.

Cognitive aging is linked to social role in honey bees (Apis mellifera)

Aging is associated with cognitive impairment in numerous animal species. Across taxa, decline in learning performance is linked to chronological age. The honey bee (Apis mellifera), in contrast, offers an opportunity to study such aspects of aging largely independent of age per se. This is because foraging onset can be decoupled from chronological age, although workers typically first perform tasks inside the nest and later forage outside the hive. Further, early phases of foraging are characterized by growth of specific brain neuropiles, whereas late phases of the forager life-stage are accompanied by accelerated rates of physiological senescence. Yet, it is unclear if these patterns of senescence include cognitive function. The flexibility of worker ontogeny, however, suggests that the bee can become an attractive model for studies of plasticity in cognitive aging that ultimately may lead to insight into mechanisms that govern age-related cognitive decline. To address this potential, we studied effects of honey bee chronological age and of social role on sensory sensitivity and associative olfactory learning performance. Our results show a decline in olfactory acquisition performance that is linked to social role, but not to chronological age. This decline occurs only in foragers with long foraging duration, but at the same time the foragers show less generalization of odors, which is indicative of more precise learning. Foragers that are reversed from foraging to nest tasks, furthermore, do not show deficits in olfactory acquisition. These results point to complex effects of aging on associative learning in honey bees.

Contextual interference in recognition memory with age

Previous behavioral research suggests that although elderly adults' memory benefits from supportive context, misleading or irrelevant contexts produce greater interference. In the present study, we use event-related fMRI to investigate age differences when processing contextual information to make recognition judgments. Twenty-one young and twenty elderly incidentally encoded pictures of objects presented in meaningful contexts, and completed a memory test for the objects presented in identical or novel contexts. Elderly committed more false alarms than young when novel objects were presented in familiar, but task-irrelevant, contexts. Elderly showed reduced engagement of bilateral dorsolateral prefrontal cortex and anterior cingulate relative to young, reflecting disruption of a cognitive control network for processing context with age. Disruption occurred for both high and low-performing elderly, suggesting that cognitive control deficits are pervasive with age. Despite showing disruption of the cognitive control network, high-performing elderly recruited additional middle and medial frontal regions that were not recruited by either low-performing elderly or young adults. This suggests that high-performing elderly may compensate for the disruption of the cognitive control network by recruiting additional frontal resources to overcome cognitive control deficits that affect recognition memory.

Adult but not aged C57BL/6 male mice are capable of using geometry for orientation

Geometry, e.g., the shape of the environment, can be used by numerous animal species to orientate, but data concerning the mouse are lacking. We addressed the question of whether mice are capable of using geometry for navigating. To test whether aging could affect searching strategies, we compared adult (3- to 5-mo old) and aged (20- to 21-mo old) C57BL/6 male mice. We established a water maze task in which spatial information is provided by one landmark proximal to the target (featural information) and by the rectangular shape of the maze (geometric information). By means of probe trials in which we manipulated the presence of these two kinds of information, we show that adult mice can use both geometry and landmark to orientate. By contrast, aged mice do not use geometry and rely exclusively on the landmark to locate the platform. This study provides the first evidence that mice are capable of using geometric information for orientation and that this ability declines in aged animals.

Explaining age differences in temporal working memory

To determine the cognitive mechanisms underlying age differences in temporal working memory (WM), the authors examined the contributions of item memory, associative memory, simple order memory, and multiple item memory, using parallel versions of the delayed-matching-to-sample task. Older adults performed more poorly than younger adults on tests of temporal memory, but there were no age differences in nonassociative item memory, regardless of the amount of information to be learned. In contrast, a combination of associative and simple order memory, both of which were reduced in older adults, completely accounted for age-related declines in temporal memory. The authors conclude that 2 mechanisms may underlie age differences in temporal WM, namely, a generalized decline in associative ability and a specific difficulty with order information.

Are space and time automatically integrated in episodic memory?

The aim of the present study was to determine to what extent spatial and temporal features are automatically integrated during encoding in episodic memory. Both nameable and non-nameable stimuli were presented sequentially at different locations on a computer screen. Mixed and pure blocks of trials were used. In the mixed blocks participants were instructed to focus either on the spatial or the temporal order of the objects, as on the majority of the trials recall of this feature was tested (expected trials). However, on a few trials participants had to reproduce the other feature (unexpected trials). In the pure blocks either the spatial or the temporal order of the objects was tested on all trials. More errors were made on unexpected than on expected trials of the mixed blocks. Moreover, no primacy or recency effects were found when performance on the spatial task was plotted as a function of the temporal position. These results suggest that spatial information and temporal order information rely on separate encoding processes.

Functional senescence in Drosophila melanogaster

The fruit fly Drosophila melanogaster is one of the principal model organisms used for studying the biology of aging. Flies are well suited for such studies for a number of reasons. Flies develop to adulthood quickly, have a relatively short life span, and are inexpensive to house. Most of the fly genome has been sequenced, powerful genetic tools are available to manipulate it, and most fly genes have obvious homologues in mammals. While the majority of aging studies in flies have focused on regulation of life span, the fly is emerging as a powerful model system for investigating the biology that underlies age-related functional decline. Key to the use of flies in this way is the striking number of parallels between functional senescence in Drosophila and humans. Here, we review age-related functional declines in Drosophila, human correlates of these age-related declines, and common mechanisms that influence longevity and specific aspects of functional senescence in flies.

Rats with scopolamine- or MK-801-induced spatial discrimination deficits in the cone field task: animal models for impaired spatial orientation performance

Spatial cognition appears to be compromised in elderly and in patients suffering from dementia. These deficits are believed to be modelled, at least partly, by the administration of scopolamine or MK-801 in normal adult animals. In order to establish an animal model suited for the evaluation of putative cognition enhancers, we assessed the effects of scopolamine (0.3, 0.5, 0.7 mg kg(-1), i.p.) and MK-801 (0.07, 0.08, 0.09 mg kg(-1), s.c.) in rats trained in the cone field. This task allows the simultaneous investigation of working memory (WM), reference memory (RM) and search strategies. Scopolamine and MK-801 reliably induced spatial cognition deficits in the cone field without inducing behavioural side effects. This task appears to be suited for assessing the effects of putative cognition-enhancing compounds on spatial cognition.

Virtual navigation in humans: the impact of age, sex, and hormones on place learning

Certain cognitive processes, including spatial ability, decline with normal aging. Spatial ability is also a cognitive domain with robust sex differences typically favoring males. However, tests of spatial ability do not seem to measure a homogeneous class of processes. For many, mentally matching rotated three-dimensional images is the gold standard for measuring spatial cognition in humans, while the Morris water task (MWT) is a preferred method in the domain of nonhuman animal research. The MWT is sensitive to hippocampal damage, a structure critical for normal learning and memory and often implicated in age-related cognitive decline. A computerized (virtual) version of the MWT (VMWT) appears to require and engage human hippocampal circuitry, and has proven useful in studying sex differences and testing spatial learning theories. In Experiment 1, we tested participants (20-90 years of age) in the VMWT and compared their performance to that on the Vandenberg Mental Rotation Test. We report an age-related deficit in performance on both tasks. In Experiment 2, we tested young (age 20-39) and elderly (age >60) participants in the VMWT and correlated their performance to the circulating levels of testosterone and cortisol. Our findings indicate that the persistence of male spatial advantage may be related to circulating testosterone, but not cortisol levels, and independent of generalized age-related cognitive decline.

The Aging Hippocampus: Navigating Between Rat and Human Experiments

Aging is associated with impairments in certain aspects of cognition, especially learning and memory. The hippocampus is a structure intimately involved with certain aspects of learning and memory, and is especially vulnerable to the course of aging. Recent findings, primarily from cognitive, magnetic resonance imaging, and magnetic resonance spectroscopy studies, but also briefly physiology and neurogenesis work, are reviewed. Evidence suggests that age-related impairment of hippocampus-dependent cognition is associated with changes on various levels of investigation in both humans and non-human animals. Also, the emphasis is placed on tasks and techniques that can be used to test both non-human and human animals in an attempt to bridge the gulf between the vast bodies of knowledge about the hippocampus in different species. To the extent that changes with normal aging are understood, they may aid in diagnosis, prevention, and/or treatment of age-related learning and memory deficits in both normal and pathological aging. In addition, studies of the aging hippocampus may have a side-effect in leading to a better understanding of the mechanisms that underlie learning and memory in general.

Memory for temporal context: Effects of ageing, encoding instructions, and retrieval strategies

Young and older adults were compared on a list discrimination task. In Experiment 1, performance declined with ageing after incidental and intentional encoding of the temporal context. Moreover, there was no benefit for intentional encoding in either group. In Experiment 2, each list was associated with a different encoding context. There were age differences in performance when participants tried to retrieve the encoding context of the items as a cue for their list of occurrence, but not when participants evaluated temporal distance from the strength of the memory trace. This suggests that the age-related decrease in list discrimination could be at least partly due to a difficulty in inferring strategically the temporal context of the items from information encoded in the same time.

Preserved spatial memory over brief intervals in older adults

Two studies compared young and older adults' memory for location information after brief intervals. Experiment 1 found that accuracy of intentional spatial memory for individual locations was similar in young and older participants for set sizes of 3 and 6. Both groups also encoded individual locations in relation to the larger configuration of locations. Experiment 2 showed that like young adults, older adults' latency to respond to a test probe in a letter working memory task was negatively influenced by spatial information that was irrelevant to the task. This interference effect indicated preserved incidental memory for spatial information in older adults. Together, these data suggest that initial encoding of spatial information for relatively small numbers of items is largely preserved in healthy older adults and that representations of spatial information persist over short intervals.

The effects of aging on location-based and distance-based processes in memory for time

Retrieving when an event occurred may depend on an estimation of the age of the event (distance-based processes) or on strategic reconstruction processes based on contextual information associated with the event (location-based processes). Young and older participants performed a list discrimination task that has been designed to dissociate the contribution of both types of processes. An adapted Remember/Know/Guess procedure [Can. J. Exp. Psychol. 50 (1996) 114] was developed to evaluate the processes used by the participants to recognize the stimuli and retrieve their list of occurrence. The results showed that aging disrupts location-based processes more than distance-based processes. In addition, a limitation of speed of processing and working-memory capacities was the main predictor of age-related differences on location-based processes, whereas working-memory capacities mediated partly age differences on distance-based processes.

Later developments: molecular keys to age-related memory impairment

Age-related memory impairment, a cognitive decline not clearly related to any gross pathology, is progressive and widespread in the population, although not universal. While the mechanisms of learning and memory remain incompletely understood, the study of their molecular mechanisms is already yielding promising approaches toward therapy for such "normal" declines in the efficiency of learning. This review presents the rationale and results for two such approaches. One approach, partial inhibition of the type IV cAMP specific phosphodiesterase, appears to act indirectly. Although little evidence supports an age-related decline in this system, considerable evidence indicates that this approach can facilitate the transition from short-term to long-term memory and thus counterbalance defects in long-term memory, which may be due to other causes. A second approach, inhibition of l-type voltage gated calcium channels (LVGCCs) may be a specific corrective for a molecular pathology of aging, as substantial evidence indicates that an ongoing increase occurs throughout the lifespan in the density of these channels in hippocampal pyramidal cells, with a concomitant reduction in cellular excitability. Because LVGCCs are also crucial to extinction, a paradigm of inhibitory learning, age-related memory impairment may be an unfortunate side effect of a developmental process necessary to the maturation of the ability to suppress inappropriate behavior, an interpretation consistent with the antagonistic pleiotropy theory of aging.

Impact of aging on hippocampal function: plasticity, network dynamics, and cognition

Aging is associated with specific impairments of learning and memory, some of which are similar to those caused by hippocampal damage. Studies of the effects of aging on hippocampal anatomy, physiology, plasticity, and network dynamics may lead to a better understanding of age-related cognitive deficits. Anatomical and electrophysiological studies indicate that the hippocampus of the aged rat sustains a loss of synapses in the dentate gyrus, a loss of functional synapses in area CA1, a decrease in the NMDA-receptor-mediated response at perforant path synapses onto dentate gyrus granule cells, and an alteration of Ca(2+) regulation in area CA1. These changes may contribute to the observed age-related impairments of synaptic plasticity, which include deficits in the induction and maintenance of long-term potentiation (LTP) and lower thresholds for depotentiation and long-term depression (LTD). This shift in the balance of LTP and LTD could, in turn, impair the encoding of memories and enhance the erasure of memories, and therefore contribute to cognitive deficits experienced by many aged mammals. Altered synaptic plasticity may also change the dynamic interactions among cells in hippocampal networks, causing deficits in the storage and retrieval of information about the spatial organization of the environment. Further studies of the aged hippocampus will not only lead to treatments for age-related cognitive impairments, but may also clarify the mechanisms of learning in adult mammals.

Parallel effects of aging and time pressure on memory for source: evidence from the spacing effect

Two experiments address the degree to which item memory-the ability to remember that a word has been presented-is dissociable from source memory, or the ability to remember the context of that word's presentation. Spacing (as opposed to massing) an item's two presentations leads young adults to endorse that item more often when they are instructed to recognize it and to reject it more often when they are instructed to exclude it. Old adults also enjoy beneficial effects of spacing when the item is to be recognized, but suffer detrimental effects of the spacing manipulation when the item is to be rejected: They falsely endorse the spaced to-be-rejected items more than the massed ones. This dissociation also obtains with young subjects under conditions of increased time pressure: Under normal decision conditions, the ability to endorse to-be-recognized items and to reject to-be-rejected items increases with spacing; under speeded conditions, the ability to reject the latter items decreases with spacing. The results support the notion that source memory is selectively impaired in the elderly and that it is difficult to access mnemonic information about source under time pressure.

Corticosteroids and cognition

The brain is a major target organ for corticosteroids. It has been observed that excessive circulatory levels of endogenous and exogenous corticosteroids are frequently associated with cognitive impairment in a wide variety of clinical disease states. Cognition and low levels of corticosteroids have been less well studied. In this paper we review the literature on glucocorticosteroid effects on cognition and delineate specific functions that appear to be causally affected. We draw a possible connection to specific areas of brain perturbation, including the hippocampus and frontal lobe regions. The possibility that cognitive dysfunction caused by glucocorticoids can be pharmacologically managed is introduced.

Age-related defects in spatial memory are correlated with defects in the late phase of hippocampal long-term potentiation in vitro and are attenuated by drugs that enhance the cAMP signaling pathway

To study the physiological and molecular mechanisms of age-related memory loss, we assessed spatial memory in C57BL/B6 mice from different age cohorts and then measured in vitro the late phase of hippocampal long-term potentiation (L-LTP). Most young mice acquired the spatial task, whereas only a minority of aged mice did. Aged mice not only made significantly more errors but also exhibited greater individual differences. Slices from the hippocampus of aged mice exhibited significantly reduced L-LTP, and this was significantly and negatively correlated with errors in memory. Because L-LTP depends on cAMP activation, we examined whether drugs that enhanced cAMP would attenuate the L-LTP and memory defects. Both dopamine D1/D5 receptor agonists, which are positively coupled to adenylyl cyclase, and a cAMP phosphodiesterase inhibitor ameliorated the physiological as well as the memory defects, consistent with the idea that a cAMP-protein kinase A-dependent signaling pathway is defective in age-related spatial memory loss.

In search of better route guidance instructions

Safety concerns have prompted designers of in-vehicle route guidance and information systems (IVRGIS) to make more use of an 'audible interface' to convey guidance instructions. Previous research has shown that, contrary to expectations, detailed guidance instructions can have a detrimental effect upon wayfinding performance, particularly for elderly individuals. In response to these findings a second series of experiments was carried out to try to improve the effectiveness of route guidance. Using the same procedure, 40 male and 40 female drivers aged 18-35 years watched video footage of journeys through an unfamiliar area, while hearing guidance that linked direction instructions to landmarks visible at the decision point. Results showed that those who heard these amended instructions performed significantly better than other groups at a wide range of tasks designed to measure the spatial knowledge that they had acquired. This group performed better than groups who heard nothing, and groups who heard full guidance. The results support the view that, whereas full guidance instructions can have a negative impact upon wayfinding performance, less complex instructions that link landmarks to directions have the capacity to enhance wayfinding performance. This is because instructions of this form strengthen the associations made between directions to be taken and the spatial location of these turns, resulting in the formation of a strong representation of the route. The results also showed that those who had been driving for 1 year or less were significantly less accurate at these tasks than those with more driving experience. This result has important implications for the widespread implementation and use of IVRGIS: suggesting that, for newly qualified drivers, who have not yet developed the ability to attend to and process information while controlling the vehicle, attending to route guidance instructions might have a detrimental effect upon driver safety.

Aging effects on the startle response and startle plasticity in Fischer F344 rats

The effects of aging on acoustic and airpuff startle reactivity, acoustic and airpuff startle habituation, acoustic and cross-modal (light-acoustic) prepulse inhibition (PPI), and fear-potentiated startle (FPS) were examined using 3- (Y: young), 11- (AD: adult), 17- (MA: middle-aged), and 22- (O: old) month-old Fischer F344 rats. AD rats had the highest acoustic startle reactivity with the Y and MA rats showing smaller and comparable startle levels. The O rats had diminished startle reactivity, with over a 65% reduction in responding. Airpuff startle reactivity was comparable in the Y and AD groups, while the MA and O groups had 40% and 80% reductions in airpuff startle respectively. There was an age-related increase in airpuff startle habituation. Acoustic and cross-modal PPI were reduced significantly in O rats when compared to other age groups. Finally, there were no effects of age on FPS. In summary, these studies suggest that in Fischer F344 rats, there are age-associated differences in startle reactivity, startle habituation, and PPI, but no aging effect on FPS.

The Effect of Right and Left Hemispheric Lesions on Effortful and Automatic Memory Tasks

The effect of lateralised cerebral damage on two memory tasks-free recall of words and memory of their temporal order-was investigated under intentional, incidental, and ''true incidental'' learning conditions. Ten Right Brain Damaged patients (RBD), 10 Left Brain Damaged patients (LBD), as well as 15 age-matched and 15 younger control individuals, participated in this study. It was hypothesised that effortful and automatic memory processes involve predominantly the left and right cerebral hemispheres, respectively. Automaticity was defined either by the learning conditions (i.e. incidental-automatic and intentional-effortful) or by the type of task (i.e. temporal-order-automatic and free-recall-effortful) regardless of the learning conditions. In the free recall task the RBD group outperformed the LBD group under all learning conditions. In the temporal order task, the RBD group performed worse than normal controls under all learning conditions while the LBD group performed more poorly than matched controls in the intentional and incidental but not in the ''true incidental'' learning condition. The results are discussed in terms of the relationship between effortful and automatic memory processes and cerebral lateralisation.

Direct and indirect memory measures of temporal order: younger versus older adults

The memory changes associated with age are attributed to the deterioration of the frontal lobes, as well as to the middle temporal structures. Therefore, in addition to a decline in memory for facts and events, as found impaired in amnesics, a memory decline associated with age is predicted for tasks typically found impaired in frontal lobe patients (i.e., temporal order judgment). There are conflicting findings concerning whether indirect measures of memory for facts and events are associated with age. However, there are no studies that address this issue with regard to temporal order judgment. Thirty younger and thirty older adults were tested on a list of words which was repeated five times in fixed or varying order. The number of words recalled, as well as their temporal judgments, were the direct measure of memory. The effect of consistency of order of presentation on the number of words recalled was the indirect measure of memory for temporal order. Results suggest that direct, but not the indirect measures of memory were related to age.

Effects of retention interval length on young and elderly adults' memory for spatial information

Adult age differences in spatial memory following retention intervals of various lengths were examined in 47 young and 56 elderly subjects who recalled spatial information following either a 3-, 15-, or 30-min retention interval. The elderly adults were significantly less accurate than the young adults following the 30-min retention interval only; there was no statistically significant effect of age at the 3-min and 15-min retention intervals. It is concluded that younger adults experience greater temporal stability of spatial memory than do older adults, and the relevance of the present findings for Craik's environmental support hypothesis is discussed.

Dissociations between memory for temporal order and recognition memory in aging

Young and old subjects participated in an experiment in which trials testing memory for temporal order (recency memory) and recognition memory were randomly intermixed with study trials in a continuous sequence. A dissociation was found between recency and recognition memory performance for pictorial stimuli. Relative to young adults, older adults performed at chance on recency memory trials whereas they were not impaired on recognition memory. Recency performance was correlated with measures derived from the Wisconsin Card Sorting test, whereas recognition performance was not. The results are discussed in terms of the role of the frontal lobes in temporal-order memory and of possible frontal lobe deterioration in normal aging.

Feature memory and binding in young and older adults

Intact memory for complex events requires not only memory for particular features (e.g., item, location, color, size), but also intact cognitive processes for binding the features together. Binding provides the memorial experience that certain features belong together. The experiments presented here were designed to explicate these as potentially separable sources of age-associated changes in complex memory-namely, to investigate the possibility that age-related changes in memory for complex events arise from deficits in (1) memory for the kinds of information that comprise complex memories, (2) the processes necessary for binding this information into complex memories, or (3) both of these components. Young and older adults were presented with colored items located within an array. Relative to young adults, older adults had a specific and disproportionate deficit in recognition memory for location, but not for item or for color. Also, older adults consistently demonstrated poorer recognition memory for bound information, especially when all features were acquired intentionally. These feature and binding deficits separately contribute to what have been described as older adults' context and source memory impairments.

Remembering spatial locations: effects of material and intelligence

The aim of the present work was to test some of the criteria for automaticity of spatial-location coding claimed by Hasher and Zacks, particularly individual differences (as intelligence invariance) and effortful encoding strategies. Two groups of subjects, 15 with mental retardation (Down Syndrome, mean chronological age, 20.9 yr.; mean mental age, 11.6 yr.) and 15 normal children (mean age, 11.5 yr.), were administered four kinds of stimuli (pictures, concrete words, nonsense pictures, and abstract words) at one location on a card. Subsequently, subjects were presented the items on the card's centre and were required to place the items in their original locations. Analysis indicated that those with Down Syndrome scored lower than normal children on the four tasks and that stimuli were better or worse remembered according to their characteristics, e.g., their imaginability. Results do not support some of the conditions claimed to be necessary criteria for automaticity in the recall of spatial locations as stated by Hasher and Zacks.

Angiotensin II and its 3-7 fragment improve recognition but not spatial memory in rats

The effects of angiotensin II (AII), its 3-7 fragment [AII(3-7)] and the substituted 3-7 fragment [Leu-5,AII(3-7)] given intracerebroventricularly (ICV) at the dose of 1 nmole each, on spatial memory and recognition were tested. AII(3-7) increased while Leu-5,AII(3-7) slightly decreased session to session foot shock reinforced runtime to the goal in a complex 6 chamber maze. The animals treated with AII performed in the maze similarly to saline injected controls. Overall number of errors was unchanged in all peptide treated groups in comparison with the control group. Object recognition was significantly improved in all the peptide treated groups except for the Leu-5,AII(3-7) group. The results point to the facilitation of recognition and lack of influence on, or even attenuation of, spatial memory by AII and its 3-7 fragment. Leu-5,AII(3-7) caused similar though less pronounced effects.