Effect of normal aging and of Alzheimer's disease on, episodic memory

Are the inhibitory and faciliatory effects during retrieval of semantically related items present in amnestic mild cognitive impairment?

Prefrontal functions subserve inhibition control for retrieval of semantically related items inducing forgetting 19 a-MCI patients and 29 controls underwent neuropsychological evaluation and retrieval-practice paradigm (RPP) to estimate baseline remember (BR), retrieval-induced facilitation (FAC) and retrieval-induced forgetting (RIF). A-MCI patients underwent also 3 T-MRI to assess relationship between regional grey matter (rGM) volumes and RPP indexes Behaviourally, RIF and FAC were both observed controls, while RIF only was observed in a-MCI patients. In patients but not in controls, RIF was associated with cognitive efficiency and FAC with memory performance. Patients showed also associations between BR and rGM volumes in the precuneus, no association was found between rGM volumes and RIF and FAC. A-MCI patients did not benefit from repeated practice during retrieval of studied items, which is likely due to their memory disorder. In contrast, patient cognitive efficiency would drive retrieval suppression of interfering stimuli.

Animal models of source memory

Source memory is the aspect of episodic memory that encodes the origin (i.e., source) of information acquired in the past. Episodic memory (i.e., our memories for unique personal past events) typically involves source memory because those memories focus on the origin of previous events. Source memory is at work when, for example, someone tells a favorite joke to a person while avoiding retelling the joke to the friend who originally shared the joke. Importantly, source memory permits differentiation of one episodic memory from another because source memory includes features that were present when the different memories were formed. This article reviews recent efforts to develop an animal model of source memory using rats. Experiments are reviewed which suggest that source memory is dissociated from other forms of memory. The review highlights strengths and weaknesses of a number of animal models of episodic memory. Animal models of source memory may be used to probe the biological bases of memory. Moreover, these models can be combined with genetic models of Alzheimer's disease to evaluate pharmacotherapies that ultimately have the potential to improve memory.

Retrosplenial cortex (BA 29) volumes in behavioral variant frontotemporal dementia and Alzheimer's disease

BACKGROUND

The retrosplenial cortex (RSC) is a crucial transit region between the hippocampus and cingulate cortex and has been implicated in spatial navigation and memory. Importantly, RSC atrophy is a predilection site of Alzheimer's (AD) pathology, but there have been no studies assessing structural changes in the RSC in behavioral variant frontotemporal dementia (bvFTD).

METHODS

A manual tracing method was used to calculate regional RSC volume in MRI scans from patients with bvFTD (n = 15) and AD (n = 15), as well as age- and sex-matched controls (n = 15).

RESULTS

RSC volumes were significantly reduced in the AD (p < 0.001), but not the bvFTD cohort (p > 0.1) compared to age-matched controls. RSC volumes discriminated bvFTD from AD in over 90% of the cases.

CONCLUSION

These findings provide further evidence that RSC atrophy is specific to AD, which might explain the commonly observed spatial disorientation in this patient group.

Remembering the past and planning for the future in rats

A growing body of research suggests that rats represent and remember specific earlier events from the past. An important criterion for validating a rodent model of episodic memory is to establish that the content of the representation is about a specific event in the past rather than vague information about remoteness. Recent evidence suggests that rats may also represent events that are anticipated to occur in the future. An important capacity afforded by a representation of the future is the ability to plan for the occurrence of a future event. However, relatively little is known about the content of represented future events and the cognitive mechanisms that may support planning. This article reviews evidence that rats remember specific earlier events from the past, represent events that are anticipated to occur in the future, and develops criteria for validating a rodent model of future planning. These criteria include representing a specific time in the future, the ability to temporarily disengage from a plan and reactivate the plan at an appropriate time in the future, and flexibility to deploy a plan in novel conditions.

Rats answer an unexpected question after incidental encoding

A fundamental aspect of episodic memory is that retrieval of information can occur when encoding is incidental and memory assessment is unexpected. These features are difficult to model in animals because behavioral training likely gives rise to well-learned expectations about the sequence of events. Thus, the possibility remains that animals may solve an episodic memory test by using well-learned semantic rules without remembering the episode at memory assessment. Here we show that rats can answer an unexpected question after incidental encoding in a hippocampal-dependent manner, consistent with the use of episodic memory. Rats were initially trained to report about a recent event (food versus no food) and separately searched for food where there was no expectation of being asked about the presence of food. To test episodic memory, we gave rats the opportunity to incidentally encode the presence or absence of food and unexpectedly asked them to report about the recent event. Temporary inactivation of the CA3 region of the hippocampus with bilateral infusions of lidocaine selectively eliminated the ability of rats to answer the unexpected, but not the expected, question. Our studies suggest that rats remember an earlier episode after incidental encoding based upon hippocampal-dependent episodic memory.

Validation of a rodent model of episodic memory

Episodic memory consists of representations of specific episodes that happened in the past. Modeling episodic memory in animals requires careful examination of alternative explanations of performance. Putative evidence of episodic-like memory may be based on encoding failure or expectations derived from well-learned semantic rules. In Experiment 1, rats were tested in a radial maze with study and test phases separated by a retention interval. The replenishment of chocolate (at its study-phase location) depended on two factors: time of day (morning vs. afternoon) and the presence or absence of chocolate pellets at the start of the test phase. Because replenishment could not be decoded until the test phase, rats were required to encode the study episode. Success in this task rules out encoding failure. In Experiment 2, two identical mazes in different rooms were used. Chocolate replenishment was trained in one room, and then they were asked to report about a recent event in a different room, where they had no expectation that the memory assessment would occur. Rats successfully answered the unexpected question, ruling out use of expectations derived from well-learned semantic rules. Our behavioral methods for modeling episodic memory may have broad application for assessments of genetic, neuroanatomical, neurochemical, and neurophysiological bases of both episodic memory and memory disorders such as those that occur in Alzheimer's disease.

Charakterisierung kognitiver Einbußen von Patienten mit “Mild Cognitive Impairment” (MCI) in der CERAD- Screeningbatterie

Zusammenfassung: Die frühzeitige Diagnose kognitiver Abbauprozesse ist vor dem Hintergrund der “alternden Gesellschaft” von enormer Bedeutung. In der vorliegenden Arbeit wurde das Potenzial der CERAD-kognitiven Screeningbatterie als Untersuchungsprotokoll zur Diagnostik leichter kognitiver Beeinträchtigungen (MCI, Petersen et al., 1995 ) sowie als Verlaufsinstrument überprüft. Die Leistungen von 51 MCI-Patienten wurden mit 81 gesunden Kontrollpersonen verglichen. Die Leistungen der MCI-Gruppe unterschied sich in nahezu allen Subtests der CERAD-Batterie signifikant von denen der Kontrollgruppe. In der Verlaufsuntersuchung an einer Teilstichprobe (n = 18) fanden sich hingegen in der CERAD-Batterie keine signifikanten Veränderungen. Zusammenfassend lässt sich feststellen, dass die CERAD-Batterie bei leichten kognitiven Beeinträchtigungen ein ausreichend valides Screeninginstrument darstellt; für Verlaufsuntersuchungen scheint sie hingegen weniger gut geeignet zu sein.

Inhibitory functioning in Alzheimer’s disease

We present a comprehensive review of studies assessing inhibitory functioning in Alzheimer's disease. The objectives of this review are: (i) to establish whether Alzheimer's disease affects all inhibitory mechanisms equally, and (ii) where possible, to assess whether any effects of Alzheimer's disease on inhibition tasks might be caused by other cognitive deficits, such as slowed processing. We review inhibitory mechanisms considered to play a crucial role in various domains of cognition, such as inhibition involved in working memory, selective attention and shifting abilities, and the inhibition of motor and verbal responses. It was found that whilst most inhibitory mechanisms are affected by the disorder, some are relatively preserved, suggesting that inhibitory deficits in Alzheimer's disease may not be the result of a general inhibitory breakdown. In particular, the experimental results reviewed showed that Alzheimer's disease has a strong effect on tasks requiring controlled inhibition processes, such as the Stroop task. However, the presence of the disease appears to have relatively little effect on tasks requiring more automatic inhibition, such as the inhibition of return task. Thus, the distinction between automatic, reflexive inhibitory mechanisms and controlled inhibitory mechanisms may be critical when predicting the integrity of inhibitory mechanisms in Alzheimer's disease. Substantial effects of Alzheimer's disease on tasks such as negative priming, which are not cognitively complex but do require some degree of controlled inhibition, support this hypothesis. A meta-analytic review of seven studies on the Stroop paradigm revealed substantially larger effects of Alzheimer's disease on the inhibition condition relative to the baseline condition, suggesting that these deficits do not simply reflect general slowing.

The cognitive-enhancing properties of modafinil are limited in non-sleep-deprived middle-aged volunteers

Modafinil is a selective wakefulness-promoting agent that has been shown to enhance cognitive performance under conditions of sleep deprivation but which has equivocal effects in normal young volunteers. In a double-blind parallel group design study, 45 non-sleep-deprived middle-aged volunteers (20 men and 25 women, aged 50-67 years) were randomly allocated to receive two capsules containing placebo, 100 or 200 mg modafinil, and 3 h later they completed 100 mm visual analogue scales of mood and bodily symptoms, before and after an extensive battery of cognitive tests [pen and paper and the Cambridge Neuropsychological Test Automated Battery (CANTAB)]. There were no significant treatment-associated changes in ratings of mood or bodily symptoms and no significant effects on most of the cognitive tests used in this study. The group treated with modafinil (200 mg) was significantly faster in a simple colour naming of dots and also significantly better in a test of constructional ability (Clock Drawing Test) compared with the placebo group. However, subjects in the 200-mg group also made significantly more total errors in the Intra/Extradimensional Set Shift (ID/ED) task than both the other groups. Thus, this study found limited evidence of cognitive-enhancing properties of modafinil in healthy middle-aged volunteers.

Changes in explicit memory associated with early dementia in adults with Down's syndrome

BACKGROUND

A modified version of the Selective Reminding Test (SRT) (Buschke 1973) was used to examine the changes in memory that occur with early-stage dementia of the Alzheimer's type (DAT) in adults with intellectual disability (ID) and Down's syndrome (DS), and to compare these changes to those occurring with 'normal' ageing.

METHOD

Hierarchical linear modelling analyses showed steep declines in the performance of participants who had met the criteria for the onset of DAT. Non-demented participants also showed declines in performance which were related to their age. However, the absolute magnitude of these declines was consistent with a 'normal' ageing pattern and not with undetected dementia.

RESULTS

In analysing the specific memory components that are compromised, the present authors found that participants with early-stage DAT showed severely diminished long-term storage and retrieval processing abilities compared to their non-demented peers. Notably, these declines preceded other symptoms of dementia, in most cases by more than a full year and sometimes by as much as 3 years.

CONCLUSIONS

Thus, the present results clearly confirm that memory processes are affected during early dementia in adults with DS, and that the SRT has promise as a clinical tool.

The canine as a model of human cognitive aging: recent developments

1. Aged dogs display many of the cognitive impairments associated with aging and dementia. 2. Aged dogs, like humans, display a wide range of individual variability in cognitive functioning (i.e., different cognitive functions decline at different rates in aged dogs). 3. Different categories of aged canines can be identified on the basis of neuropsychological test performance, and these categories can be used to model different subgroups of aged humans (i.e., dementia, mild cognitive impairment and successful aging). 4. Additional research is required to further validate the dog as a model of human cognitive aging and dementia.

Experimental and clinical methods in the development of anti-Alzheimer drugs

Methodology used for the development of anti-Alzheimer's disease (AD) drugs raises specific problems which are rarely examined in the literature. While the general development scheme is similar to that required for most drugs, some specific aspects must be analyzed, highly dominated by the dual goal of pharmacology, i.e., to obtain both symptomatic and etiopathogenic drugs. During preclinical studies, aged or lesioned animals are mainly useful for symptomatic drugs, whereas transgenic models or neurodegeneration-induced techniques would probably lead to etiopathogenic drugs potentially slowing down the process of AD. The first administrations of a new compound to human beings raise the question of the activity measurement techniques. Psychometry remains the most informative procedure to detect and analyze the activity of the drugs on the different components of cognition. Electrophysiology and neuroimaging need some complementary studies before they can be proposed as surrogate criteria in phase III trials. At this stage of development, American and the recently published European guidelines are of great help while insisting on long-term (6 months) placebo controlled trials with the use of the triple efficacy criterion: an objective cognition scale, a global assessment, and the opinion of the caregiver. In the long term, pharmacoepidemiology and pharmacoeconomy will have to confirm the rationale of this recent progress in the methodology of anti-AD drug development.