Associative and recognition memory for novel objects in dementia: implications for diagnosis

Visual short-term memory binding and attentional processes during object-scene integration are preserved in mild cognitive impairment

Binding, a critical cognitive process likely mediated by attention, is essential for creating coherent object representations within a scene. This process is vulnerable in individuals with dementia, who exhibit deficits in visual working memory (VWM) binding, primarily tested using abstract arrays of standalone objects. To explore how binding operates in more realistic settings across the lifespan, we examined the impact of object saliency and semantic consistency on VWM binding and the role of overt attention. Using an eye-tracking change detection task, we compared younger adults, healthy older adults, and individuals with Mild Cognitive Impairment (MCI). Participants were presented with naturalistic scenes and asked to detect changes in the identity and/or location of objects that were either semantically consistent or inconsistent with their scene context. Across all age groups, semantically inconsistent objects were prioritised during encoding, leading to better change detection than consistent objects. Highly salient objects decreased the inconsistency advantage while being detrimental to detection accuracy when inspected at longer latencies to the first fixation. Longer fixation durations on the critical object were beneficial for recognition. In contrast, delayed initial inspection or frequent subsequent fixations on other objects were detrimental to detection, regardless of age or cognitive impairment. These findings challenge the notion of generalised semantic memory impairment in the prodromal stages of dementia and highlight the importance of efficient attentional control in supporting VWM binding, even in the face of cognitive decline. Overall, preserved low-level and high-level mechanisms of object-scene integration can compensate for age-related cognitive decline, enabling successful binding in naturalistic contexts.

Cognitive aging and reserve factors in the Metropolit 1953 Danish male cohort

Identifying early predictors of cognitive decline and at-risk individuals is essential for timely intervention and prevention of dementia. This study aimed to detect neurobiological changes and factors related to cognitive performance in the Metropolit 1953 Danish male birth cohort. We analyzed data from 582 participants, aged 57-68 years, using machine learning techniques to group cognitive trajectories into four clusters differentiating high- and low-performing groups. These clusters were then evaluated with MRI, EEG, and lifestyle/familial risk factors to identify predictors of cognitive decline. Low education and occupation, alcohol consumption, and type 2 diabetes were associated with lower cognitive performance. Declines in neocortical volume and increases in frontotemporal alpha and temporoparietal gamma activity preceded clinical symptoms of cognitive decline. Neocortical atrophy and disruptions in network activity were prominent in lower-performing groups, with higher education and IQ scores and a lower prevalence of lifestyle factors moderating cognitive decline.

Longitudinal assessment of cognitive function in the APPswe/PS1dE9 mouse model of Alzheimer's-related beta-amyloidosis

Preclinical models of Alzheimer's disease (AD)-related cognitive decline can be useful for developing therapeutics. The current study longitudinally assessed short-term memory, using a delayed matching-to-position (DMTP) task, and attention, using a 3-choice serial reaction time (3CSRT) task, from approximately 18 weeks of age through death or 72 weeks of age in APPswe/PS1dE9 mice, a widely used mouse model of AD-related amyloidosis. Both transgenic (Tg) and non-Tg mice exhibited improvements in DMTP accuracy over time. Breaks in testing reduced DMTP accuracy but accuracy values quickly recovered in both Tg and non-Tg mice. Both Tg and non-Tg mice exhibited high accuracy in the 3CSRT task with breaks in testing briefly reducing accuracy values equivalently in the 2 genotypes. The current results raise the possibility that deficits in Tg APPswe/PS1dE9 mice involve impairments in learning rather than declines in established performances. A better understanding of the factors that determine whether deficits develop will be useful for designing evaluations of potential pharmacotherapeutics and may reveal interventions for clinical application.

Differences in auditory associative memory between younger adults and older adults

Aging impairs visual associative memories. Up to date, little is known about whether aging impairs auditory associative memories. Using the head-related-transfer function to induce perceived spatial locations of auditory phonemes, this study used an audiospatial paired-associates-learning (PAL) paradigm to assess the auditory associative memory for phoneme-location pairs in both younger and older adults. Both aging groups completed the PAL task with various levels of difficulty, which were defined by the number of items to be remembered. The results showed that compared with younger participants' performance, older participants passed fewer stages and had lower capacity of auditory associative memory. For maintaining a single audiospatial pair, no significant behavioral differences between the two aging grous werefound. However, when multiple sound-location pairs were required to be remembered, older adults made more errors and demonstrated a lower working memory capacity than younger adults. Our study indicates aging impairs audiospatial associative learning and memory.

Sleep contributes to preference for novel food odours in Drosophila melanogaster

The importance of sleep in maintaining cognitive functions such as learning and memory has been reported in both vertebrates and invertebrates. Previous studies demonstrated that sleep deprivation impaired the olfactory memory retention of fruit flies as described in the classical conditioning paradigm. Here, we show that sleep deprivation leads to a preference for the odours of the rearing environment in Drosophila melanogaster. Flies whose sleep had been disturbed with periodic rotation stimuli during night-time preferred apple cider vinegar (ACV) to broth, while this preference was lower in flies without sleep deprivation and those rotated during daytime. Experiments using single odours showed an increase in responses to ACV due to sleep deprivation. These results suggest that sleep functions in food odour preference. Flies grown on medium supplemented with ACV showed greater preference for ACV, and those grown with broth supplementation showed a greater preference for broth under sleep-deprived conditions. These results suggest that flies with night-time sleep deprivation become attached to the environment on which they have developed, and that sleep contributes to preference for novel food odours. This study offers an approach to investigating the interaction between sleep and neural disorders concerning cognitive deficits towards novel stimuli.

Behavioral shaping of rhesus macaques using the Cambridge neuropsychological automated testing battery

BACKGROUND

The Cambridge neuropsychological test automated battery (CANTAB) is a set of computerized visuospatial tests used to probe cognition in humans. The non-human primate (NHP) version of the battery is a valuable translational research tool to quantify cognitive changes in NHP models of disease by allowing direct comparison with performance data from human patient populations. One limitation is the long training times required for NHPs to reach appropriate levels of task performance, which is prohibitive for high throughput experimental designs.

NEW METHOD

We report a new training regimen to teach NHPs a subset of CANTAB cognitive tasks using a method of successive approximations (shaping), where rewarded behaviors progressively approximate the goal behavior, and sequential task learning is used to build upon previously learned rules. Using this refined method, we taught 9 adult rhesus macaques to perform three tasks: the self-ordered spatial search (SOSS), delayed match-to-sample (DMTS), and paired associative learning (PAL) tasks.

RESULTS AND COMPARISON WITH EXISTING METHODS

NHPs learned all three cognitive tasks in approximately 130 training sessions, roughly 200 sessions faster than previously published training times. NHPs were able to perform each task to a stable level of performance (>80 % correct) enabling their use in future cognitive experiments.

CONCLUSIONS

Our approach of behavioral shaping reduced the time to train NHPs to performance criteria on SOSS, DMTS, and PAL tasks. This allows efficient use of the NHP-adapted CANTAB to compare cognitive changes in NHP models of neurological disease with those observed in human patient populations.

Thirty-Five Years of Computerized Cognitive Assessment of Aging-Where Are We Now?

Over the past 35 years, the proliferation of technology and the advent of the internet have resulted in many reliable and easy to administer batteries for assessing cognitive function. These approaches have great potential for affecting how the health care system monitors and screens for cognitive changes in the aging population. Here, we review these new technologies with a specific emphasis on what they offer over and above traditional 'paper-and-pencil' approaches to assessing cognitive function. Key advantages include fully automated administration and scoring, the interpretation of individual scores within the context of thousands of normative data points, the inclusion of 'meaningful change' and 'validity' indices based on these large norms, more efficient testing, increased sensitivity, and the possibility of characterising cognition in samples drawn from the general population that may contain hundreds of thousands of test scores. The relationship between these new computerized platforms and existing (and commonly used) paper-and-pencil tests is explored, with a particular emphasis on why computerized tests are particularly advantageous for assessing the cognitive changes associated with aging.

Predicting progression to Alzheimer's disease in subjects with amnestic mild cognitive impairment using performance on recall and recognition tests

The research of reliable procedures for predicting cognitive decline or stability in persons with amnestic mild cognitive impairment (a-MCI) is a major goal for the early identification of subjects in the prodromal stages of dementia. The aim of this study was to evaluate whether different memory performances on two procedures commonly used for the neuropsychological assessment of episodic memory (i.e., free recall and recognition) might be a key in predicting a-MCI patients' subsequent progression to Alzheimer's disease (AD). For this purpose, 80 patients diagnosed with a-MCI at the first assessment and followed-up for at least 3 years were included. During this time, 41 subjects remained in a stable condition of cognitive impairment or improved (stable-MCI) and 39 patients converted to AD dementia (converter-MCI). Sixty-two age- and education-matched healthy individuals were also recruited as healthy controls (HC). Baseline memory performance on the free recall (5th immediate and 15-min delayed) and yes/no recognition (the sensitivity measure d') of a 15-word list were analyzed. Results showed that stable-MCIs forgot significantly more information from immediate to delayed recall of the word list than HC, but exhibited a pronounced improvement of memory performance in the recognition test format. On the contrary, converter-MCIs showed diminished sensitivity in benefiting from cues for recognizing studied words. Word list recognition correctly classified group membership with good overall accuracy, which was higher compared to the classification of converter and stable a-MCIs provided by free recall; therefore, it could be a useful diagnostic tool for predicting progression to AD dementia from the prodromal stage.

Basal forebrain cholinergic system volume is associated with general cognitive ability in the elderly

OBJECTIVE

At the present, it is unclear whether association of basal forebrain cholinergic system (BFCS) volume with cognitive performance exists in healthy as well as in cognitively impaired elderly subjects. Whereas one small study reported an association of BFCS volume with general cognitive ability 'g' in healthy ageing, effects on specific cognitive domains have only been found in subjects with cognitive decline. Here we aim to clarify whether an association of BFCS volume and 'g' is present in a larger sample of elderly subjects without obvious symptoms of dementia and whether similar associations can also be observed in specific cognitive domains.

METHODS

282 pre-surgical patients from the BioCog study (aged 72.7 ± 4.9 years with a range of 65-87 years, 110 women) with a median MMSE score of 29 points (range 24-30) were investigated. BFCS and brain volume as well as brain parenchymal fraction were assessed in T1-weighted MR images using SPM12 and a probabilistic map of the BFCS. Neuropsychological assessment comprised the CANTAB cognitive battery and paper-and-pencil based tests. For data analysis, generalised linear models and quantile regression were applied.

RESULTS

Significant associations of BFCS volume with 'g' and several cognitive domains were found, with the strongest association found for 'g'. BFCS volume explained less variance in cognitive performance than brain volume. The association was not confounded by brain parenchymal fraction. Furthermore, the association of BFCS volume and 'g' was similar in high- and low-performers.

CONCLUSION

Our results extend previous study findings on BFCS volume associations with cognition in elderly subjects. Despite the observed associations of BFCS volume and cognitive performance, this association seems to reflect a more general association of brain volume and cognition. Accordingly, a specific association of BFCS volume and cognition in non-demented elderly subjects is questionable.

Impaired perceptual integration and memory for unitized representations are associated with perirhinal cortex atrophy in Alzheimer's disease

Unitization, the capacity to encode associations as one integrated entity, can enhance associative memory in populations with an associative memory deficit by promoting familiarity-based associative recognition. Patients with Alzheimer's disease (AD) are typically impaired in associative memory compared with healthy controls but do not benefit from unitization strategies. Using fragmented pictures of objects, this study aimed at assessing which of the cognitive processes that compose unitization is actually affected in AD: the retrieval of unitized representations itself, or some earlier stages of processing, such as the integration process at a perceptual or conceptual stage of representation. We also intended to relate patients' object unitization capacity to the integrity of their perirhinal cortex (PrC), as the PrC is thought to underlie unitization and is also one of the first affected regions in AD. We evaluated perceptual integration capacity and subsequent memory for those items that have supposedly been unitized in 23 mild AD patients and 20 controls. We systematically manipulated the level of perceptual integration during encoding by presenting object pictures that were either left intact, separated into 2 fragments, or separated into 4 fragments. Subjects were instructed to unitize the fragments into a single representation. Success of integration was assessed by a question requiring the identification of the object. Participants also underwent a structural magnetic resonance imaging examination, and measures of PrC, posterior cingulate cortex volume and thickness, and hippocampal volume, were extracted. The results showed that patients' perceptual integration performance decreased with the increased fragmentation level and that their memory for unitized representations was impaired whatever the demands in terms of perceptual integration at encoding. Both perceptual integration and memory for unitized representations were related to the integrity of the PrC, and memory for unitized representations was also related to the volume of the hippocampus. We argue that, globally, this supports representational theories of memory that hold that the role of the PrC is not only perceptual nor mnemonic but instead underlies complex object representation.

Physical Exercise During Pregnancy Prevents Cognitive Impairment Induced by Amyloid-β in Adult Offspring Rats

Alzheimer's disease (AD) is the main aging-associated neurodegenerative disorder and is characterized by mitochondrial dysfunction, oxidative stress, synaptic failure, and cognitive decline. It has been a challenge to find disease course-modifying treatments. However, several studies demonstrated that regular physical activity and exercise are capable of promoting brain health by improving the cognitive function. Maternal lifestyle, including regular exercise during pregnancy, has also been shown to influence fetal development and disease susceptibility in adulthood through fetal metabolism programming. Here, we investigated the potential neuroprotective role of regular maternal swimming, before and during pregnancy, against amyloid-β neurotoxicity in the adult offspring. Behavioral and neurochemical analyses were performed 14 days after male offspring received a single, bilateral, intracerebroventricular (icv) injection of amyloid-β oligomers (AβOs). AβOs-injected rats of the sedentary maternal group exhibited learning and memory deficits, along with reduced synaptophysin, brain-derived neurotrophic factor (BDNF) levels, and alterations of mitochondrial function. Strikingly, the offspring of the sedentary maternal group had AβOs-induced behavioral alterations that were prevented by maternal exercise. This effect was accompanied by preventing the alteration of synaptophysin levels in the offspring of exercised dams. Additionally, offspring of the maternal exercise group exhibited an augmentation of functional mitochondria, as indicated by increases in mitochondrial mass and membrane potential, α-ketoglutarate dehydrogenase, and cytochrome c oxidase enzymes activities. Moreover, maternal exercise during pregnancy induced long-lasting modulation of fusion and fission proteins, Mfn1 and Drp1, respectively. Overall, our data demonstrates a potential protective effect of exercise during pregnancy against AβOs-induced neurotoxicity in the adult offspring brain, by mitigating the neurodegenerative process triggered by Alzheimer-associated AβOs through programming the brain metabolism.

Meta-analytic Review of Memory Impairment in Behavioral Variant Frontotemporal Dementia

OBJECTIVES

A meta-analysis of the extent, nature and pattern of memory performance in behavioral variant frontotemporal dementia (bvFTD). Multiple observational studies have challenged the relative sparing of memory in bvFTD as stated in the current diagnostic criteria.

METHODS

We performed a meta-analytic review covering the period 1967 to February 2017 of case-control studies on episodic memory in bvFTD versus control participants (16 studies, 383 patients, 603 control participants), and patients with bvFTD versus those with Alzheimer's disease (AD) (20 studies, 452 bvFTD, 874 AD). Differences between both verbal and non-verbal working memory, episodic memory learning and recall, and recognition memory were examined. Data were extracted from the papers and combined into a common metric measure of effect, Hedges' d.

RESULTS

Patients with bvFTD show large deficits in memory performance compared to controls (Hedges' d -1.10; 95% confidence interval [CI] [-1.23, -0.95]), but perform significantly better than patients with AD (Hedges' d 0.85; 95% CI [0.69, 1.03]). Learning and recall tests differentiate best between patients with bvFTD and AD (p<.01). There is 37-62% overlap in test scores between the two groups.

CONCLUSIONS

This study points to memory disorders in patients with bvFTD, with performance at an intermediate level between controls and patients with AD. This indicates that, instead of being an exclusion criterion for bvFTD diagnosis, memory deficits should be regarded as a potential integral part of the clinical spectrum. (JINS, 2018, 24, 593-605).

Can visuospatial measures improve the diagnosis of Alzheimer's disease?

Introduction

Overlapping and evolving symptoms lead to ambiguity in the diagnosis of dementia. Visuospatial function relies on parietal lobe function, which may be affected in the early stages of Alzheimer's disease (AD). This review evaluates visuospatial dysfunction in patients with AD, frontotemporal dementia, dementia with Lewy bodies, and vascular dementia to determine the diagnostic and prognostic potential of visuospatial tasks in AD.

Methods

A systematic search of studies (1960–2016) investigating visuospatial dysfunction in dementia was conducted.

Results

Tests measuring construction, specifically Block Design and Clock Drawing Test, and visual memory, specifically Rey-Osterrieth Complex Figure recall and topographical tasks, show the greatest diagnostic potential in dementia. The Benton visual retention, Doors and People, and topographical memory tests show potential as prognostic markers.

Discussion

Tests of visuospatial function demonstrate significant diagnostic and prognostic potential in dementia. Further studies with larger samples of pathologically confirmed cases are required to verify clinical utility.

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Memory deficits have been demonstrated in Alzheimer's and non-Alzheimer's dementias.

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Parietal lobes are uniquely affected in the early stages of Alzheimer's disease.

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Visuospatial tasks demonstrate significant diagnostic and prognostic potential.

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Computerized test protocols have been developed to test aspects of visuospatial function and memory.

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Novel topographical memory tasks demonstrated the greatest prognostic potential.

Neuropsychological Investigations of Human Amnesia: Insights Into the Role of the Medial Temporal Lobes in Cognition

The past 30 years of research on human amnesia has yielded important changes in our understanding of the role of the medial temporal lobes (MTL) in memory. On the one hand, this body of evidence has highlighted that not all types of memory are impaired in patients with MTL lesions. On the other hand, this research has made apparent that the role of the MTL extends beyond the domain of long-term memory, to include working memory, perception, and future thinking. In this article, we review the discoveries and controversies that have characterized this literature and that set the stage for a new conceptualization of the role of the MTL in cognition. This shift toward a more nuanced understanding of MTL function has direct relevance for a range of clinical disorders in which the MTL is implicated, potentially shaping not only theoretical understanding but also clinical practice. (JINS, 2017, 23, 732-740).

NAAG Peptidase Inhibitors Act via mGluR3: Animal Models of Memory, Alzheimer's, and Ethanol Intoxication

Glutamate carboxypeptidase II (GCPII) inactivates the peptide neurotransmitter N-acetylaspartylglutamate (NAAG) following synaptic release. Inhibitors of GCPII increase extracellular NAAG levels and are efficacious in animal models of clinical disorders via NAAG activation of a group II metabotropic glutamate receptor. mGluR2 and mGluR3 knock-out (ko) mice were used to test the hypothesis that mGluR3 mediates the activity of GCPII inhibitors ZJ43 and 2-PMPA in animal models of memory and memory loss. Short- (1.5 h) and long- (24 h) term novel object recognition tests were used to assess memory. Treatment with ZJ43 or 2-PMPA prior to acquisition trials increased long-term memory in mGluR2, but not mGluR3, ko mice. Nine month-old triple transgenic Alzheimer's disease model mice exhibited impaired short-term novel object recognition memory that was rescued by treatment with a NAAG peptidase inhibitor. NAAG peptidase inhibitors and the group II mGluR agonist, LY354740, reversed the short-term memory deficit induced by acute ethanol administration in wild type mice. 2-PMPA also moderated the effect of ethanol on short-term memory in mGluR2 ko mice but failed to do so in mGluR3 ko mice. LY354740 and ZJ43 blocked ethanol-induced motor activation. Both GCPII inhibitors and LY354740 also significantly moderated the loss of motor coordination induced by 2.1 g/kg ethanol treatment. These data support the conclusion that inhibitors of glutamate carboxypeptidase II are efficacious in object recognition models of normal memory and memory deficits via an mGluR3 mediated process, actions that could have widespread clinical applications.

An in Silico, Biomarker-Based Method for the Evaluation of Virtual Neuropsychiatric Drug Effects

The recent explosion in neuroscience research has markedly increased our understanding of the neurobiological correlates of many psychiatric illnesses, but this has unfortunately not translated into more effective pharmacologic treatments for these conditions. At the same time, researchers have increasingly sought out biological markers, or biomarkers, as a way to categorize psychiatric illness, as these are felt to be closer to underlying genetic and neurobiological vulnerabilities. While biomarker-based drug discovery approaches have tended to employ in vivo (e.g., rodent) or in vitro test systems, relatively little attention has been paid to the potential of computational, or in silico, methodologies. Here we describe such a methodology, using as an example a biophysically detailed computational model of hippocampus that is made to generate putative schizophrenia biomarkers by the inclusion of a number of neuropathological changes that have been associated with the illness (NMDA system deficit, decreased neural connectivity, hyperdopaminergia). We use the specific inability to attune to gamma band (40 Hz) auditory stimulus as our illness biomarker. We expose this system to a large number of virtual medications, defined by systematic variation of model parameters corresponding to five cellular-level effects. The potential efficacy of virtual medications is determined by a wellness metric (WM) that we have developed. We identify a number of virtual agents that consist of combinations of mechanisms, which are not simply reversals of the causative lesions. The manner in which this methodology could be extended to other neuropsychiatric conditions, such as Alzheimer's disease, autism, and fragile X syndrome, is discussed.

Pupillary responses and memory-guided visual search reveal age-related and Alzheimer's-related memory decline

Episodic memory - composed of memory for unique spatiotemporal experiences - is known to decline with aging, and even more severely in Alzheimer 's disease (AD). Memory for trial-unique objects in spatial scenes depends on the integrity of the hippocampus and interconnected structures that are among the first areas affected in AD. We reasoned that memory for objects-in-scenes would be impaired with aging, and that further impairments would be observed in AD. We asked younger adults, healthy older adults, older adults at-risk for developing cognitive impairments, and older adults with probable early AD to find changing items ('targets') within images of natural scenes, measuring repeated-trial changes in search efficiency and pupil diameter. Compared to younger adults, older adults took longer to detect target objects in repeated scenes, they required more fixations and those fixations were more dispersed. Whereas individuals with AD showed some benefit of memory in this task, they had substantially longer detection times, and more numerous, dispersed fixations on repeated scenes compared to age-matched older adults. Correspondingly, pupillary responses to novel and repeated scenes were diminished with aging and further in AD, and the memory-related changes were weaker with aging and absent in AD. Our results suggest that several nonverbal measures from memory-guided visual search tasks can index aging and Alzheimer's disease status, including pupillary dynamics. The task measurements are sensitive to the integrity of brain structures that are associated with Alzheimer's-related neurodegeneration, the task is well tolerated across a range of abilities, and thus, it may prove useful in early diagnostics and longitudinal tracking of memory decline.

The Paired Associates Learning (PAL) Test: 30 Years of CANTAB Translational Neuroscience from Laboratory to Bedside in Dementia Research

The origins and rationale of the Cambridge Neuropsychological Test Automated Battery (CANTAB) as a cross-species translational instrument suitable for use in human neuropsychopharmacological studies are reviewed. We focus on its use for the early assessment and detection of Alzheimer's disease, in particular the Paired Associates Learning (PAL) test. We consider its psychometric properties, neural validation, and utility, including studies on large samples of healthy volunteers, patients with mild cognitive impairment (MCI), and Alzheimer's disease. We demonstrate how it can be applied in cross-species studies using experimental animals to bridge the cross-species translational 'gap'. We also show how the CANTAB PAL has bridged a second translational 'gap' through its application to the early detection of memory problems in primary care clinics, using iPad technology.

Potential neuroprotective effect of lithium in bipolar patients evaluated by neuropsychological assessment: preliminary results

OBJECTIVE

Accumulating evidence is delineating a neuroprotective/neurotrophic role for lithium. However, its primary effects on cognition remain ambiguous. We sought to investigate the profile of cognitive impairment in patients with bipolar disorder and to determine whether continued treatment with lithium preserves cognitive functioning.

METHODS

In this cross-sectional study, we tested 15 euthymic patients with bipolar I disorder undergoing long-term clinical maintenance treatment with lithium (for at least 12 months), 15 matched patients treated with other mood-stabilizing drugs and who had never received lithium, and 15 matched healthy subjects on the Cambridge Neuropsychological Test Automated Battery. Investigated cognitive domains were visual memory, executive functions, attention, decision-making/impulsivity, and response inhibition. We controlled for age, gender, intelligence, and residual psychiatric symptomatology.

RESULTS

Taken together, bipolar patients demonstrated robust deficits in visual memory and executive functions. Once subdivided in treatment subgroups, only non-lithium bipolar patients demonstrated impairments in visual memory. Attention, decision-making, and response inhibition were preserved in both groups. No correlation emerged between neuropsychological tests performance, clinical, and psychological variables.

CONCLUSIONS

This study is the first to our knowledge to have demonstrated, by means of a highly sensitive test of visual memory, a potential hippocampus neuroprotective effect of lithium in patients with bipolar disorder. Besides, it confirms prior findings of cognitive deficits in euthymic bipolar patients.

APOE-ε4 selectively modulates posteromedial cortex activity during scene perception and short-term memory in young healthy adults

Apolipoprotein E (APOE) ε4 is a major genetic risk factor for Alzheimer’s disease (AD), yet the mechanisms by which APOE-ε4 influences early-life brain function, and hence, in turn, risk for later-life AD, are poorly understood. Here, we report a novel, and selective, pattern of functional brain activity alteration in healthy young adult human APOE-ε4 carriers. Our findings suggest that APOE-ε4 may influence vulnerability to poorer later life cognitive health via its effect on posteromedial cortex (PMC), a hub region within a brain network involved in spatial processing, and necessary for episodic memory. In two neuroimaging tasks, APOE-ε4 carriers showed an inability to effectively modulate PMC during scene, but not face and object, working memory and perception. This striking pattern overlaps both functionally and topographically, with the earliest cognitive deficits seen in clinical AD, as well as reported alterations in the default network in amyloid-positive individuals at increased risk of AD.

Associative memory and its cerebral correlates in Alzheimer׳s disease: evidence for distinct deficits of relational and conjunctive memory

This study investigated the impact of Alzheimer׳s disease (AD) on conjunctive and relational binding in episodic memory. Mild AD patients and controls had to remember item-color associations by imagining color either as a contextual association (relational memory) or as a feature of the item to be encoded (conjunctive memory). Patients׳ performance in each condition was correlated with cerebral metabolism measured by FDG-PET. The results showed that AD patients had an impaired capacity to remember item-color associations, with deficits in both relational and conjunctive memory. However, performance in the two kinds of associative memory varied independently across patients. Partial Least Square analyses revealed that poor conjunctive memory was related to hypometabolism in an anterior temporal-posterior fusiform brain network, whereas relational memory correlated with metabolism in regions of the default mode network. These findings support the hypothesis of distinct neural systems specialized in different types of associative memory and point to heterogeneous profiles of memory alteration in Alzheimer׳s disease as a function of damage to the respective neural networks.

PDE9A inhibition rescues amyloid beta-induced deficits in synaptic plasticity and cognition

The cyclic nucleotide cGMP is an important intracellular messenger for synaptic plasticity and memory function in rodents. Therefore, inhibition of cGMP degrading phosphodiesterases, like PDE9A, has gained interest as potential target for treatment of cognition deficits in indications like Alzheimer's disease (AD). In fact, PDE9A inhibition results in increased hippocampal long-term potentiation and exhibits procognitive effects in rodents. To date, however, no evidence has been published linking PDE9A inhibition to the pathologic hallmarks of AD such as amyloid beta (Aβ) deposition. Therefore, we investigated the role of PDE9A inhibition in an AD relevant context by testing its effects on Aβ-related deficits in synaptic plasticity and cognition. The PDE9A inhibitor BAY 73-6691 was found to restore long-term potentiation impaired by Aβ42 oligomers. Furthermore, we demonstrated that BAY 73-6691 enhanced cGMP levels in the hippocampus of APP transgenic tg2576 mice and improved memory performance of these mice. Altogether, our results support the hypothesis that inhibition of PDE9A could be a beneficial approach for the treatment of memory impairment in AD patients.

Social influence on associative learning: double dissociation in high-functioning autism, early-stage behavioural variant frontotemporal dementia and Alzheimer's disease

INTRODUCTION

Most of our learning activity takes place in a social context. I examined how social interactions influence associative learning in neurodegenerative diseases and atypical neurodevelopmental conditions primarily characterised by social cognitive and memory dysfunctions.

METHODS

Participants were individuals with high-functioning autism (HFA, n = 18), early-stage behavioural variant frontotemporal dementia (bvFTD, n = 16) and Alzheimer's disease (AD, n = 20). The leading symptoms in HFA and bvFTD were social and behavioural dysfunctions, whereas AD was characterised by memory deficits. Participants received three versions of a paired associates learning task. In the game with boxes test, objects were hidden in six candy boxes placed in different locations on the computer screen. In the game with faces, each box was labelled by a photo of a person. In the real-life version of the game, participants played with real persons.

RESULTS

Individuals with HFA and bvFTD performed well in the computer games, but failed on the task including real persons. In contrast, in patients with early-stage AD, social interactions boosted paired associates learning up to the level of healthy control volunteers. Worse performance in the real life game was associated with less successful recognition of complex emotions and mental states in the Reading the Mind in the Eyes Test. Spatial span did not affect the results.

CONCLUSIONS

When social cognition is impaired, but memory systems are less compromised (HFA and bvFTD), real-life interactions disrupt associative learning; when disease process impairs memory systems but social cognition is relatively intact (early-stage AD), social interactions have a beneficial effect on learning and memory.

Blueberry Supplemented Diet: Effects on Object Recognition Memory and Nuclear Factor-kappa B Levels in Aged Rats

It has been reported that an antioxidant-rich, blueberry-supplemented rat diet may retard brain aging in the rat. The present study determined whether such supplementation could prevent impaired object recognition memory and elevated levels of the oxidative stress-responsive protein, nuclear factor-kappa B (NF-kappaB) in aged Fischer-344 rats. Twelve aged rats had been fed a 2% blueberry supplemented diet for 4 months prior to testing. Eleven aged rats and twelve young rats had been fed a control diet. The rats were tested for object recognition memory on the visual paired comparison task. With a 1-h delay between training and testing, aged control diet rats performed no better than chance. Young rats and aged blueberry diet rats performed similarly and significantly better than the aged control diet group. Levels of NF-kappaB in five brain regions of the above subjects were determined by western blotting assays. In four regions, aged control diet rats had significantly higher average NF-kappaB levels than young animals on the control diet. In four regions, aged blueberry diet rats had significantly lower levels of NF-kappaB than aged control diet rats. Normalized NF-kappaB levels (averaged across regions and in several individual regions) correlated negatively and significantly with the object memory scores.

Dissociation of explicit and implicit long-term memory consolidation in semantic dementia: a case study

We report a case study of a semantic dementia patient, whose episodic memory consolidation was tested over a 2-month period. The results reveal that despite early retention of information, the patient lost all explicit information of the newly learnt material after 2 weeks. By contrast, he retained implicit word information even after a 4-week delay. These findings highlight the critical time window of 2-4 weeks in which newly learnt information should be re-encoded in rehabilitations studies. The results also indicate that learnt information can be still accessed with implicit retrieval strategies when explicit retrieval fails.

Memory for action sequences in semantic dementia

Semantic dementia (SD) is associated with a progressive, relatively selective, degeneration of semantic memory (both verbal and nonverbal facts and knowledge). Episodic memory, however, is thought to be relatively preserved. This study aimed to further assess the nonverbal, incidental, episodic memory profile associated with SD using deferred imitation, which measures recall by the nonverbal imitation of novel action sequences after a 24-h delay. The performance of six individuals with SD was compared to that of 10 healthy age- and education-matched controls. After a baseline phase, where sets of objects were presented for manipulation to measure the spontaneous production of relevant action sequences, participants were shown eight novel three-step action sequences with the sets of objects. The component actions of the sequences were causally related in four of the eight series and arbitrarily related in the remaining four, to investigate the influence of sequence structure on memory performance. All participants produced more target actions and pairs in the arbitrary sequences 24-h after demonstration compared to baseline, indicating memory for the sequences, but only the control group showed significant memory for the order of the causal sequences (pairs). Furthermore, and perhaps more strikingly, only the control participants showed a recall advantage for the causal relative to the arbitrary sequences, indicating that they, but not the patients, could take advantage of the semantic nature of these sequences. Together these findings suggest that individuals with SD show some nonverbal episodic memory, even after a 24-h delay, and that new anterograde memory can to some extent be established without significant support from semantic memory.

A preclinical cognitive test battery to parallel the National Institute of Health Toolbox in humans: bridging the translational gap

A major goal of animal research is to identify interventions that can promote successful aging and delay or reverse age-related cognitive decline in humans. Recent advances in standardizing cognitive assessment tools for humans have the potential to bring preclinical work closer to human research in aging and Alzheimer's disease. The National Institute of Health (NIH) has led an initiative to develop a comprehensive Toolbox for Neurologic Behavioral Function (NIH Toolbox) to evaluate cognitive, motor, sensory and emotional function for use in epidemiologic and clinical studies spanning 3 to 85 years of age. This paper aims to analyze the strengths and limitations of animal behavioral tests that can be used to parallel those in the NIH Toolbox. We conclude that there are several paradigms available to define a preclinical battery that parallels the NIH Toolbox. We also suggest areas in which new tests may benefit the development of a comprehensive preclinical test battery for assessment of cognitive function in animal models of aging and Alzheimer's disease.

Item familiarity and controlled associative retrieval in Alzheimer's disease: an fMRI study

Typical Alzheimer's disease (AD) is characterized by an impaired form of associative memory, recollection, that includes the controlled retrieval of associations. In contrast, familiarity-based memory for individual items may sometimes be preserved in the early stages of the disease. This is the first study that directly examines whole-brain regional activity during one core aspect of the recollection function: associative controlled episodic retrieval (CER), contrasted to item familiarity in AD patients. Cerebral activity related to associative CER and item familiarity in AD patients and healthy controls (HCs) was measured with functional magnetic resonance imaging during a word-pair recognition task to which the process dissociation procedure was applied. Some patients had null CER estimates (AD-), whereas others did show some CER abilities (AD+), although significantly less than HC. In contrast, familiarity estimates were equivalent in the three groups. In AD+, as in controls, associative CER activated the inferior precuneus/posterior cingulate cortex (PCC). When performing group comparisons, no region was found to be significantly more activated during CER in HC than AD+ and vice versa. However, during associative CER, functional connectivity between this region and the hippocampus, the inferior parietal and dorsolateral prefrontal cortex (DLPFC) was significantly higher in HC than in AD+. In all three groups, item familiarity was related to activation along the intraparietal sulcus (IPS). In conclusion, whereas the preserved automatic detection of an old item (without retrieval of accurate word association) is related to parietal activation centred on the IPS, the inferior precuneus/PCC supports associative CER ability in AD patients, as in HC. However, AD patients have deficient functional connectivity during associative CER, suggesting that the residual recollection function in these patients might be impoverished by the lack of some recollection-related aspects such as autonoetic quality, episodic details and verification.

NAAG peptidase inhibitors and deletion of NAAG peptidase gene enhance memory in novel object recognition test

The peptide neurotransmitter N-acetylaspartylglutamate (NAAG) is inactivated by the extracellular enzyme glutamate carboxypeptidase II. Inhibitors of this enzyme reverse dizocilpine (MK-801)-induced impairment of short-term memory in the novel object recognition test. The objective of this study was to test the hypothesis that NAAG peptidase inhibition enhances long-term (24h delay) memory of C57BL mice. These mice and mice in which glutamate carboxypeptidase II had been knocked out were presented with two identical objects to explore for 10min on day 1 and tested with one of these familiar objects and one novel object on day 2. Memory was assessed as the degree to which the mice recalled the familiar object and explored the novel object to a greater extent on day 2. Uninjected mice or mice injected with saline prior to the acquisition session on day 1 demonstrated a lack of memory of the acquisition experience by exploring the familiar and novel objects to the same extent on day 2. Mice treated with glutamate carboxypeptidase II inhibitors ZJ43 or 2-PMPA prior to the acquisition trial explored the novel object significantly more time than the familiar object on day 2. Consistent with these results, mice in which glutamate carboxypeptidase II had been knocked out distinguished the novel from the familiar object on day 2 while their heterozygous colony mates did not. Inhibition of glutamate carboxypeptidase II enhances recognition memory, a therapeutic action that might be useful in treatment of memory deficits related to age and neurological disorders.

APP transgenic mice for modelling behavioural and psychological symptoms of dementia (BPSD)

The discovery of gene mutations responsible for autosomal dominant Alzheimer's disease has enabled researchers to reproduce in transgenic mice several hallmarks of this disorder, notably Aβ accumulation, though in most cases without neurofibrillary tangles. Mice expressing mutated and wild-type APP as well as C-terminal fragments of APP exhibit variations in exploratory activity reminiscent of behavioural and psychological symptoms of Alzheimer dementia (BPSD). In particular, open-field, spontaneous alternation, and elevated plus-maze tasks as well as aggression are modified in several APP transgenic mice relative to non-transgenic controls. However, depending on the precise murine models, changes in open-field and elevated plus-maze exploration occur in either direction, either increased or decreased relative to controls. It remains to be determined which neurotransmitter changes are responsible for this variability, in particular with respect to GABA, 5HT, and dopamine.

The coumarin scopoletin potentiates acetylcholine release from synaptosomes, amplifies hippocampal long-term potentiation and ameliorates anticholinergic- and age-impaired memory

In a previous study the simple, naturally derived coumarin scopoletin (SCT) was identified as an inhibitor of acetylcholinesterase (AChE), using a pharmacophore-based virtual screening approach. In this study the potential of SCT as procholinergic and cognition-enhancing therapeutic was investigated in a more detailed way, using different experimental approaches like measuring newly synthesized acetylcholine (ACh) in synaptosomes, long-term potentiation (LTP) experiments in hippocampal slices, and behavior studies. SCT enhanced the K⁺-stimulated release of ACh from rat frontal cortex synaptosomes, showing a bell-shaped dose effect curve (E_max: 4 μM). This effect was blocked by the nicotinic ACh receptor (nAChR) antagonists mecamylamine (MEC) and dihydro-β-erythroidine (DHE). The nAChR agonist (and AChE inhibitor) galantamine induced a similar increase in ACh release (E_max: 1 μM). SCT potentiated LTP in hippocampal slices of rat brain. The high-frequency stimulation (HFS)-induced, N-methyl-D-aspartate (NMDA) receptor dependent LTP of field excitatory postsynaptic potentials at CA3-CA1 synapses was greatly enhanced by pre-HFS application of SCT (4 μM for 4 min). This effect was mimicked by nicotine (2 μM) and abolished by MEC, suggesting an effect on nAChRs. SCT did not restore the total inhibition of LTP by NMDA receptor antagonist d, l-2-amino-5-phosphonopentanoic acid (AP-5). SCT (2 μg, i.c.v.) increased T-maze alternation and ameliorated novel object recognition of mice with scopolamine-induced cholinergic deficit. It also reduced age-associated deficits in object memory of 15–18-month-old mice (2 mg/kg sc). Our findings suggest that SCT possesses memory-improving properties, which are based on its direct nAChR agonistic activity. Therefore, SCT might be able to rescue impaired cholinergic functions by enhancing nAChR-mediated release of neurotransmitters and promoting neural plasticity in hippocampus.

Specific deficit of colour-colour short-term memory binding in sporadic and familial Alzheimer's disease

Short-term memory binding of visual features which are processed across different dimensions (shape-colour) is impaired in sporadic Alzheimer's disease, familial Alzheimer's disease, and in asymptomatic carriers of familial Alzheimer's disease. This study investigated whether Alzheimer's disease also impacts on within-dimension binding processes. The study specifically explored whether visual short-term memory binding of features of the same type (colour-colour) is sensitive to Alzheimer's disease. We used a neuropsychological battery and a short-term memory binding task to assess patients with sporadic Alzheimer's disease (Experiment 1), familial Alzheimer's disease (Experiment 2) due to the mutation E280A of the Presenilin-1 gene and asymptomatic carriers of the mutation. The binding task assessed change detection within arrays of unicoloured objects (Colour Only) or bicoloured objects the colours of which had to be remembered separately (Unbound Colours) or together (Bound Colours). Performance on the Bound Colours condition (1) explained the largest proportion of variance between patients (sporadic and familial Alzheimer's disease), (2) combined more sensitivity and specificity for the disease than other more traditional neuropsychological tasks, (3) identified asymptomatic carriers of the mutation even when traditional neuropsychological measures and other measures of short-term memory did not and, (4) contrary to shape-colour binding, correlated with measures of hippocampal functions. Colour-colour binding and shape-colour binding both appear to be sensitive to AD even though they seem to rely on different brain mechanisms.

Beta-adrenergic receptors link NO/sGC/PKG signaling to BDNF expression during the consolidation of object recognition long-term memory

The nitric oxide (NO)/soluble guanylyl cyclase (sGC)/protein kinase G (PKG) pathway is important for memory processing, but the identity of its downstream effectors as well as its actual participation in the consolidation of nonaversive declarative long-term memory (LTM) remain unknown. Here, we show that training rats in an object recognition (OR) learning task rapidly increased nitrites/nitrates (NOx) content in the CA1 region of the dorsal hippocampus while posttraining intra-CA1 microinfusion of the neuronal NO synthase (nNOS) inhibitor L-NN hindered OR LTM retention without affecting memory retrieval or other behavioral variables. The amnesic effect of L-NN was not state dependent, was mimicked by the sGC inhibitor LY83583 and the PKG inhibitor KT-5823, and reversed by coinfusion of the NO donor S-nitroso-N-acetylpenicillamine (SNAP) and the PKG activator 8-bromoguanosine 3',5'-cyclic monophosphate (8Br-cGMP). SNAP did not affect the amnesic effect of LY83583 and KT-5823. Conversely, 8Br-cGMP overturned the amnesia induced by LY83583 but not that caused by KT-5823. Intra-CA1 infusion of the beta-adrenergic receptor blocker timolol right after training hindered OR LTM and, although coadministration of noradrenaline reversed the amnesia caused by L-NN, LY83583, and KT5823, the amnesic effect of timolol was unaffected by coinfusion of 8Br-cGMP or SNAP, indicating that hippocampal beta-adrenergic receptors act downstream NO/sGC/PKG signaling. We also found that posttraining intra-CA1 infusion of function-blocking anti-brain-derived neurotrophic factor (BDNF) antibodies hampered OR LTM retention, whereas OR training increased CA1 BDNF levels in a nNOS- and beta-adrenergic receptor-dependent manner. Taken together, our results demonstrate that NO/sGC/PKG signaling in the hippocampus is essential for OR memory consolidation and suggest that beta-adrenergic receptors link the activation of this pathway to BDNF expression during the consolidation of declarative memories.

Using the Cambridge Neuropsychological Test Automated Battery (CANTAB) to assess the cognitive impact of electroconvulsive therapy on visual and visuospatial memory

BACKGROUND

The cognitive impact of electroconvulsive therapy (ECT) is rarely measured systematically in everyday clinical practice even though patient and clinician acceptance is limited by its adverse affect on memory. If patients are tested it is often with simple paper and pencil tests of visual or verbal memory. There are no reported studies of computerized neuropsychological testing to assess the cognitive impact of ECT on visuospatial memory.

METHOD

Twenty-four patients with severe depression were treated with a course of bilateral ECT and assessed with a battery of visual memory tests within the Cambridge Neuropsychological Test Automated Battery (CANTAB). These included spatial and pattern recognition memory, pattern-location associative learning and a delayed matching to sample test. Testing was carried out before ECT, during ECT, within the week after ECT and 1 month after ECT.

RESULTS

Patients showed significant impairments in visual and visuospatial memory both during and within the week after ECT. Most impairments resolved 1 month following ECT; however, significant impairment in spatial recognition memory remained. This is one of only a few studies that have detected anterograde memory deficits more than 2 weeks after treatment.

CONCLUSIONS

Patients receiving ECT displayed a range of visual and visuospatial deficits over the course of their treatment. These deficits were most prominent for tasks dependent on the use of the right medial temporal lobe; frontal lobe function may also be implicated. The CANTAB appears to be a useful instrument for measuring the adverse cognitive effects of ECT on aspects of visual and visuospatial memory.

How preserved is episodic memory in behavioral variant frontotemporal dementia?

OBJECTIVE

Studies have shown variable memory performance in patients with behavioral variant frontotemporal dementia (bvFTD). Our study investigated whether this variability is due to the admixture of patients with true bvFTD and phenocopy patients. We also sought to compare performance of patients with bvFTD and patients with Alzheimer disease (AD).

METHODS

We analyzed neuropsychological memory performance in patients with a clinical diagnosis of bvFTD divided into those who progressed (n = 50) and those who remained stable (n = 39), patients with AD (n = 64), and healthy controls (n = 64).

RESULTS

Patients with progressive bvFTD were impaired on most memory tests to a similar level to that of patients with early AD. Findings from a subset of patients with progressive bvFTD with confirmed FTLD pathology (n = 10) corroborated these findings. By contrast, patients with phenocopy bvFTD performed significantly better than progressors and patients with AD. Logistic regression revealed that patients with bvFTD can be distinguished to a high degree (85%) on the immediate recall score of a word list learning test (Rey Auditory Verbal Learning Test).

CONCLUSIONS

Our results provide evidence for an underlying memory deficit in "real" or progressive behavioral variant frontotemporal dementia (bvFTD) similar to Alzheimer disease, though the groups differ in orientation scores, with patients with bvFTD being intact. Exclusion solely based on impaired neuropsychological memory performance can potentially lead to an underdiagnosis of FTD.

A reduction in hippocampal GABAA receptor alpha5 subunits disrupts the memory for location of objects in mice

The memory for location of objects, which binds information about objects to discrete positions or spatial contexts of occurrence, is a form of episodic memory particularly sensitive to hippocampal damage. Its early decline is symptomatic for elderly dementia. Substances that selectively reduce alpha5-GABA(A) receptor function are currently developed as potential cognition enhancers for Alzheimer's syndrome and other dementia, consistent with genetic studies implicating these receptors that are highly expressed in hippocampus in learning performance. Here we explored the consequences of reduced GABA(A)alpha5-subunit contents, as occurring in alpha5(H105R) knock-in mice, on the memory for location of objects. This required the behavioral characterization of alpha5(H105R) and wild-type animals in various tasks examining learning and memory retrieval strategies for objects, locations, contexts and their combinations. In mutants, decreased amounts of alpha5-subunits and retained long-term potentiation in hippocampus were confirmed. They exhibited hyperactivity with conserved circadian rhythm in familiar actimeters, and normal exploration and emotional reactivity in novel places, allocentric spatial guidance, and motor pattern learning acquisition, inhibition and flexibility in T- and eight-arm mazes. Processing of object, position and context memories and object-guided response learning were spared. Genotype difference in object-in-place memory retrieval and in encoding and response learning strategies for object-location combinations manifested as a bias favoring object-based recognition and guidance strategies over spatial processing of objects in the mutants. These findings identify in alpha5(H105R) mice a behavioral-cognitive phenotype affecting basal locomotion and the memory for location of objects indicative of hippocampal dysfunction resulting from moderately decreased alpha5-subunit contents.