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PubMed2004

Deficient arithmetic fact retrieval--storage or access problem? A case study.

This paper aims at clarifying the nature of fact retrieval difficulties in an 18-year-old young man (MO) who exhibited a puzzling pattern of developmental dyscalculia. Contrasting performance on explicit (production and verification tasks) and implicit (priming) tasks we observed poor overt retrieval of addition and multiplication facts, classical interference effects in verification tasks and inconsistency of error patterns. Hence, MO's performance pattern is suggestive of the existence of a partly stored network of facts (reflecting imperfect storage), but is also compatible with an access deficit according to Warrington and Cipolotti's [Brain 119 (1996) 611] criteria for distinguishing access and storage deficits in dysphasic patients. Furthermore, while MO displayed interference effects in verification tasks, he did not show automatic access to arithmetic facts in implicit tasks. Finally, similar to the findings of Roussel, Fayol, and Barrouillet [European Journal of Cognitive Psychology 14(1) (2002) 61] on normal subjects, MO's performance pattern is suggestive of the existence of differential processing mechanisms for addition and multiplication facts. We propose a unifying mechanism, namely a deficit of the central executive of working memory (WM), that accounts both for the constitution of a fuzzy network of fact representations, and for an access deficit modulated by attentional demands as required in explicit/implicit task paradigms. Overall, our results clearly provide evidence that even in (a developmental) case of a non-perfect network of memory representations (e.g. [Journal of Experimental Psychology: General 117 (1988) 258]), interference effects might be observed. Future studies thus need to be cautious before concluding that interference effects prove the existence of a well-established associative memory network of arithmetic facts.

Adolescent↗

PubMed2005

Orexin-saporin lesions of the medial septum impair spatial memory.

The medial septum and diagonal band of Broca (MSDB) provide a major input to the hippocampus and are important for spatial learning and memory. Although electrolytic MSDB lesions have prominent memory impairing effects, selective lesions of either cholinergic or GABAergic MSDB neurons do not or only mildly impair spatial memory. MSDB neurons are targets of orexin-containing neurons from the hypothalamus. At present, the functional significance of orexin afferents to MSDB is unclear, and the present study investigated a possible involvement of orexin innervation of the MSDB in spatial memory. Orexin-saporin, a toxin that damages neurons containing the hypocretin-2 receptor, was administered into the MSDB of rats. Rats were subsequently tested on a water maze to assess spatial reference memory and a plus maze to assess spatial working memory. At 100 ng/microl, orexin-saporin destroyed primarily GABAergic septohippocampal neurons, sparing the majority of cholinergic neurons. At 200 ng/microl, orexin-saporin almost totally eliminated GABAergic septohippocampal neurons and destroyed many cholinergic neurons. Spatial reference memory was impaired at both concentrations of orexin-saporin with a dramatic impairment observed for 24-h retention. Short-term reference memory was also impaired at both concentrations. Rats treated with 200 ng/microl, but not 100 ng/microl, of orexin-saporin were also impaired on a spontaneous alternation task, showing a deficit in spatial working memory. Our results, together with previous studies, suggest that orexin innervation of the MSDB may modulate spatial memory by acting on both GABAergic and cholinergic septohippocampal neurons.

Animals↗

PubMed2005

Dopaminergic control of working memory and its relevance to schizophrenia: a circuit dynamics perspective.

This article argues how dopamine controls working memory and how the dysregulation of the dopaminergic system is related to schizophrenia. In the dorsolateral prefrontal cortex, which is the principal part of the working memory system, recurrent excitation is subtly balanced with intracortical inhibition. A potent controller of the dorsolateral prefrontal cortical circuit is the mesocortical dopaminergic system. To understand the characteristics of the dopaminergic control of working memory, the stability of the circuit dynamics under the influence of dopamine has been studied. Recent computational studies suggest that the hyperdopaminergic state is usually stable but the hypodopaminergic state tends to be unstable. The stability also depends on the efficacy of the glutamatergic transmission in the corticomesencephalic projections to dopamine neurons. When this cortical feedback is hypoglutamatergic, the circuit of the dorsolateral prefrontal cortex tends to be unstable, such that a slight increase in dopamine releasability causes a catastrophic jump of the dorsolateral prefrontal cortex activity from a low to a high level. This may account for the seemingly paradoxical overactivation of the dorsolateral prefrontal cortex observed in schizophrenic patients. Given that dopamine transmission is abnormal in the brains of patients with schizophrenia and working memory deficit is a core dysfunction in schizophrenia, the concept of circuit stability would be useful not only for understanding the mechanisms of working memory processing but for developing therapeutic strategies to enhance cognitive functions in schizophrenia.

Dopamine↗

PubMed2005

The functional neuroanatomy of working memory: contributions of human brain lesion studies.

Studies of patients with focal brain lesions remain critical components of research programs attempting to understand human brain function. Whereas functional imaging typically reveals activity in distributed brain regions that are involved in a task, lesion studies can define which of these brain regions are necessary for a cognitive process. Further, lesion studies are less critical regarding the selection of baseline conditions needed in functional brain imaging research. Lesion studies suggest a functional subdivision of the visuospatial sketchpad of working memory with a ventral stream reaching from occipital to temporal cortex supporting object recognition and a dorsal stream connecting the occipital with parietal cortex enabling spatial operations. The phonological loop can be divided into a phonological short-term store in inferior parietal cortex and an articulatory subvocal rehearsal process relying on brain areas necessary for speech production, i.e. Broca's area, the supplementary motor association area and possibly the cerebellum. More uncertainty exists regarding the role of the prefrontal cortex in working memory. Whereas single cell studies in non-human primates and functional imaging studies in humans have suggested an extension of the ventral and dorsal path into different subregions of the prefrontal cortex, lesion studies together with recent single-cell and imaging studies point to a non-mnemonic role of the prefrontal cortex, including attentional control of sensory processing, integration of information from different domains, stimulus selection and monitoring of information held in memory. Our own data argue against a modulatory view of the prefrontal cortex and suggest that processes supporting working memory are distributed along ventral and dorsal lateral prefrontal cortex.

Attention↗

PubMed2005

Vitamins E and C pretreatment prevents ovariectomy-induced memory deficits in water maze.

We investigated whether the pretreatment with vitamins E (alpha-tocopherol) and C (ascorbic acid) would act on ovariectomy-induced memory deficits in Morris water maze tasks. Adult female Wistar rats were divided into three groups: (1) naive (control), (2) sham (submitted to surgery without removal of ovaries) and (3) ovariectomized. Thirty days after surgery, they were trained in the Morris water maze in order to verify ovariectomy effects both on reference and working memory tasks. Results show that ovariectomized rats presented impairment in spatial navigation in the acquisition phase, as well as in the time spent in target quadrant and in the latency to cross over the location of the platform in test session, when compared to naive and sham groups (controls), in the reference memory task. Ovariectomy did not affect performance in the working memory task. Confirming our hypothesis, ovariectomized rats pretreated for 30 days with vitamins E and C had those impairments prevented. We conclude that ovariectomy significantly impairs spatial reference learning/memory and that pretreatment with vitamins E and C prevents such effect. Assuming this experimental memory impairment might mimic, at least in part, the cognitive deficit sometimes present in the human condition of lack of reproductive hormones, our findings lend support to a novel therapeutic strategy, based on vitamins E and C, to cognitive impairments in post-menopausal women.

Animals↗

PubMed2006

Working memory deficits in transgenic rats overexpressing human adenosine A2A receptors in the brain.

Adenosine receptors in the central nervous system have been implicated in the modulation of different behavioural patterns and cognitive functions although the specific role of A(2A) receptor (A(2A)R) subtype in learning and memory is still unclear. In the present work we establish a novel transgenic rat strain, TGR(NSEhA2A), overexpressing adenosine A(2A)Rs mainly in the cerebral cortex, the hippocampal formation, and the cerebellum. Thereafter, we explore the relevance of this A(2A)Rs overexpression for learning and memory function. Animals were behaviourally assessed in several learning and memory tasks (6-arms radial tunnel maze, T-maze, object recognition, and several Morris water maze paradigms) and other tests for spontaneous motor activity (open field, hexagonal tunnel maze) and anxiety (plus maze) as modification of these behaviours may interfere with the assessment of cognitive function. Neither motor performance and emotional/anxious-like behaviours were altered by overexpression of A(2A)Rs. TGR(NSEhA2A) showed normal hippocampal-dependent learning of spatial reference memory. However, they presented working memory deficits as detected by performance of constant errors in the blind arms of the 6 arm radial tunnel maze, reduced recognition of a novel object and a lack of learning improvement over four trials on the same day which was not observed over consecutive days in a repeated acquisition paradigm in the Morris water maze. Given the interdependence between adenosinic and dopaminergic function, the present results render the novel TGR(NSEhA2A) as a putative animal model for the working memory deficits and cognitive disruptions related to overstimulation of cortical A(2A)Rs or to dopaminergic prefrontal dysfunction as seen in schizophrenic or Parkinson's disease patients.

Analysis of Variance↗

PubMedDate not supplied

Cocaine in adolescent rats produces residual memory impairments that are reversible with time.

Rats received injections (subcutaneous) of either 10 or 20 mg/kg cocaine on postnatal days 26-33, while lab chow-fed and pair-fed controls received saline. Spatial memory in a Morris water maze was assessed on four different occasions commencing 10 days postcocaine and ending approximately 12 months later. To determine whether there existed long-term changes in cholinergic processes, maze performance was evaluated following 1 mg/kg scopolamine challenge 4 months postcocaine. Subjects survived under standard laboratory housing conditions until they died. Results from the first assessment indicated a working memory deficit in the low-dose cocaine group and a long-term memory impairment in the high-dose cocaine group. These decrements neither were permanent nor were exacerbated by age-related processes in that cocaine-treated subjects performed at control levels on subsequent assessments. An exception to this was the results derived from the third assessment indicating that animals previously treated with 20 mg/kg cocaine were impaired when challenged with scopolamine. Examination of mortality rates revealed that cocaine-treated rats died significantly sooner than lab chow-fed control subjects. Taken together, these data indicate that cocaine during adolescence causes residual, but not permanent, deleterious effects on memory that may be mediated by alterations in cholinergic neurochemistry. More provocatively, the results showed that cocaine during adolescence shortened the lifespan of rats. This latter finding suggests that cocaine during adolescence may produce residual physiological effects that last well into adulthood.

Age Factors↗

PubMed2004

Improvement of scopolamine-induced memory impairment by Z-ajoene in the water maze in mice.

Z-ajoene, a major compound containing sulfur in oil-macerated garlic products, exhibited inhibitory effects against scopolamine-induced memory impairment in mice using the Morris water maze test. The effects of Z-ajoene were observed dose-dependently (0.25-25 mg/kg). At the highest dosage, the memory performance of mice was improved compared to normal mice. The acetylcholinesterase (AChE) activity in the brain was reduced by administration of Z-ajoene dose-dependently. However, alliin and diallyl disulfide, organosulfur compounds from garlic, did not improve memory performance nor AChE inhibitory effect. These results suggest that Z-ajoene may act on the cholinergic system and on memory impairment caused by excess activity of AChE.

Acetylcholinesterase↗

PubMed2005

St John's wort (Hypericum perforatum) diminishes cognitive impairment caused by the chronic restraint stress in rats.

In this study we tested the hypothesis that St John's wort (Hypericum perforatum) may counteract stress-induced memory impairment. Object recognition test and Morris water maze were used to determine whether administration of H. perforatum (350 mg kg(-1) for 21 days), standardized to 0.3% hypericin content, protects against non-spatial and/or spatial memory impairments due to chronic restraint stress (2h daily for 21 days). A group of rats administered the exogenous corticosterone at the dose of 5 mg kg(-1) daily for 21 days, yielding its similar plasma levels as these observed in stress was run in parallel. In the first experiment all rats were tested for recognition memory in the object recognition test. On the following day, the animals were tested in open field and elevated "plus" maze to control for the contribution of respectively, motor and emotional effects of our treatments to the memory tests. In the second experiment, new group of stressed animals was tested for spatial memory in the water maze. We observed that H. perforatum prevented the deleterious effects of both chronic restraint stress and long-term corticosterone on learning and memory as measured in both, the object recognition and the water maze tests. The herb not only prevented stress- and corticosterone-induced memory impairments, but it significantly improved recognition memory (p<0.01) in comparison to control. These results suggest that H. perforatum has a potential to prevent stress memory disorders.

Animals↗

PubMed2005

The canine model of human cognitive aging and dementia: pharmacological validity of the model for assessment of human cognitive-enhancing drugs.

For the past 15 years we have investigated the aged beagle dog as a model for human aging and dementia. We have shown that dogs develop cognitive deficits and neuropathology seen in human aging and dementia. These similarities increase the likelihood that the model will be able to accurately predict the efficacy of Alzheimer's disease (AD) treatments as well as detect therapeutics with limited or no efficacy. Better predictive validity of cognitive-enhancing therapeutics (CETs) could lead to enormous cost savings by reducing the number of failed human clinical trials and also may reduce the likelihood of negative outcomes such as those recently observed in the AN-1792 clinical trials. The current review assesses the pharmacological validity of the canine model of human aging and dementia. We tested the efficacy of (1) CP-118,954 and phenserine, two acetylcholinesterase inhibitors, (2) an ampakine, (3) selegiline hydrochloride, two drugs that have failed human AD trials, and (4) adrafinil, a putative CET. Our research demonstrates that dogs not only develop isomorphic changes in human cognition and brain pathology, but also accurately predict the efficacy of known AD treatments and the absence or limited efficacy of treatments that failed clinical trials. These findings collectively support the utilization of the dog model as a preclinical screen for identifying novel CETs for both age-associated memory disorder and dementia.

Aging↗

PubMed2004

Memory impairment and auditory evoked potential gating deficit in schizophrenia.

Impaired sensory gating and memory function were reported in a study of 10 schizophrenic patients and 10 age- and sex-matched normal subjects. The P50 component of the auditory evoked potential was used as an index of gating. Explicit memory was tested with the Wechsler Memory Scale and implicit memory by artificial grammar learning. The schizophrenic patients showed deficits in both verbal paired associate and visual reproduction tasks. They demonstrated impaired implicit learning in color patterns but not letter strings. They also showed impaired P50 sensory gating. Three-dimensional brain mapping revealed a differential distribution of brain potentials in the processing of S1 and S2 at either P50 or N100 in both groups. However, the group difference was not statistically confirmed. In the controls, both implicit letter-string learning and explicit verbal paired associates were positively correlated with N100 gating, suggesting an association of the early attentive component with lexicons. In the schizophrenic patients, color-pattern implicit learning was positively correlated with P50 gating. The modality-specific impairment of implicit learning in schizophrenia may reflect a failure of adaptive filtering on the flooding input from color patterns.

Adult↗

PubMed2004

Intranasal insulin improves memory in humans.

Previous studies have suggested an acutely improving effect of insulin on memory function. To study changes in memory associated with a prolonged increase in brain insulin activity in humans, here we used the intranasal route of insulin administration known to provide direct access of the substance to the cerebrospinal fluid compartment. Based on previous results indicating a prevalence of insulin receptors in limbic and hippocampal regions as well as improvements in memory with systemic insulin administration, we expected that intranasal administration of insulin improves primarily hippocampus dependent declaration memory function. Also, improvements in mood were expected. We investigated the effects of 8 weeks of intranasal administration of insulin (human regular insulin 4 x 40 IU/d) on declarative memory (immediate and delayed recall of word lists), attention (Stroop test), and mood in 38 healthy subjects (24 males) in a double blind, between-subject comparison. Blood glucose and plasma insulin levels did not differ between the placebo and insulin conditions. Delayed recall of words significantly improved after 8 weeks of intranasal insulin administration (words recalled, Placebo 2.92 +/- 1.00, Insulin 6.20 +/- 1.03, p < 0.05). Moreover, subjects after insulin reported signs of enhanced mood, such as reduced anger (p < 0.02) and enhanced self-confidence (p < 0.03). Results indicate a direct action of prolonged intranasal administration of insulin on brain functions, improving memory and mood in the absence of systemic side effects. These findings could be of relevance for the treatment of patients with memory disorders like in Alzheimer's disease.

Administration, Intranasal↗

PubMed2005

Weight loss strategies, stress, and cognitive function: supervised versus unsupervised dieting.

The early stages of dieting to lose weight have been associated with neuro-psychological impairments. Previous work has not elucidated whether these impairments are a function solely of unsupported or supported dieting. Raised cortico-steroid levels have been implicated as a possible causal mechanism. Healthy, overweight, pre-menopausal women were randomised to one of three conditions in which they dieted either as part of a commercially available weight loss group, dieted without any group support or acted as non-dieting controls for 8 weeks. Testing occurred at baseline and at 1, 4 and 8 weeks post baseline. During each session, participants completed measures of simple reaction time, motor speed, vigilance, immediate verbal recall, visuo-spatial processing and (at Week 1 only) executive function. Cortisol levels were gathered at the beginning and 30 min into each test session, via saliva samples. Also, food intake was self-recorded prior to each session and fasting body weight and percentage body fat were measured at each session. Participants in the unsupported diet condition displayed poorer vigilance performance (p = 0.001) and impaired executive planning function (p = 0.013) (along with a marginally significant trend for poorer visual recall (p = 0.089)) after 1 week of dieting. No such impairments were observed in the other two groups. In addition, the unsupported dieters experienced a significant rise in salivary cortisol levels after 1 week of dieting (p < 0.001). Both dieting groups lost roughly the same amount of body mass (p = 0.011) over the course of the 8 weeks of dieting, although only the unsupported dieters experienced a significant drop in percentage body fat over the course of dieting (p = 0.016). The precise causal nature of the relationship between stress, cortisol, unsupported dieting and cognitive function is, however, uncertain and should be the focus of further research.

Adult↗

PubMed2005

Memory tests in first-degree adult relatives of schizophrenic patients: a meta-analysis.

BACKGROUND: Memory deficits have been clearly demonstrated in schizophrenic patients. However, studies of memory performances in their relatives compared to normal controls provide conflicting results. A meta-analysis was carried out to synthesize all the published data. Unlike previous meta-analyses, which were based on composite scores, we analyzed each memory test separately. This prevents theoretically questionable choices in grouping variables, leads to results with clearer implications for applied research (e.g. the best choice of a test according to its sensitivity) and is more productive in suggesting explanatory hypotheses. METHOD: We initially selected 77 potentially relevant articles, but only 19 met our inclusion criteria. These articles provided data on eight different tasks, from five different memory tests: four tests from the Wechsler Memory Scale (WMS) and the California Verbal Learning Test (CVLT). For each task, we assessed data homogeneity, identified the outliers if any and then estimated effect sizes and tested publication bias using funnel plots. RESULTS: Adult relatives of schizophrenic patients were significantly impaired on most, but not all, tasks. The largest deficits were observed for the verbal paired associates test, the logical stories the digit span forward test and the digit span backward test. We found no significant differences in tasks of delayed recall, when deficits in immediate conditions (reflecting encoding) were taken into account. CONCLUSIONS: Adult relatives of schizophrenic patients have wide but not severe memory impairments. The size of estimated effects suggests that encoding processes are impaired, whereas storage and retrieval processes are relatively unaffected.

Adult↗

PubMed2006

Short-term social recognition memory deficit and atypical social and physiological stressor reactivity in seizure-susceptible El mice.

The present studies characterize working memory capabilities in the El mouse model of epilepsy using a species-typical social recognition memory task. As the El mouse exhibits a stress hyper-reactivity phenotype, the impact of hypertonic saline consumption, a memory modulatory treatment, upon social recognition performance was also examined. The hypotheses under test were: (1) that seizure susceptible El mice would perform poorly in the short-term working memory task relative to seizure resistant ddY controls, and (2) that the behavioral and neural responses to stressor exposure would be atypical in El mice. Results revealed a short-term working memory deficit and altered reactivity to social, environmental, and physiological stressors in El mice. In Experiment 1, El mice exhibited poor sociability and decreased olfactory investigation times, both anxiogenic-like traits, compared to ddY controls. In Experiment 2, El mice exhibited poor working memory performance compared to capable performance in ddY controls. Social recognition memory in ddY mice was abolished, however, by salt-loading whereas El mice were unaffected by exposure to this physiological stressor. In Experiment 3, all salt-loaded mice exhibited enhanced brain stress neuropeptide (corticotropin releasing factor-CRF) content, and salt-loaded El mice exhibited a 70% reduction in handling-induced seizures. These findings suggest that El mice exhibit high emotionality as well as atypical reactions to stressor exposure, and that these characteristics impact social working memory performance and seizure susceptibility.

Animals↗

PubMed2004

Structural versus functional prediction of memory change following anterior temporal lobectomy.

Decline in recent memory function is a significant risk for patients undergoing anterior temporal lobectomy. We report a patient with a febrile seizure history, complex partial seizures arising from the left anterior temporal lobe, and MRI evidence suggesting left hippocampal sclerosis, all of which indicate a low likelihood of significant postoperative memory decline. However, high normal verbal memory on neuropsychological testing and bilaterally normal Wada memory scores indicated increased risk for postoperative memory decline. Following left anterior temporal lobectomy, the patient displayed a significant decline in verbal recent memory that affected school performance. Despite the worsening in memory, the patient reported a significant improvement in his self-reported quality-of-life perception, demonstrating that factors other than change in cognitive performance are related to whether a patient considers epilepsy surgery worthwhile. In the present case, behavioral measures were superior to structural measures in predicting cognitive change following surgery.

Adult↗

PubMed2005

Epilepsy increases vulnerability of long-term face recognition to proactive interference.

Proactive interference (PI) decreases short- and long-term memory in healthy subjects. Neurological patients exhibit a heightened PI effect on short-term memory. It is, however, not known if PI affects long-term memory in neurological patients. We analyzed whether epilepsy heightens the negative effect of PI on long-term face memory. PI was induced by a list of 20 faces learned 24 hours prior to a target list of 20 faces. We tested immediate and 24-hour recognition for both lists. Twelve healthy controls and 42 patients with generalized epilepsy or temporal lobe epilepsy (TLE) were studied. PI led to a decrease in 24-hour recognition in patients with generalized epilepsy and TLE but not in controls. Thus, PI may cause long-term memory disturbances in epilepsy patients. PI was also associated with decreased short-term memory, but only in right TLE. This confirms the dominant role of the right temporal lobe in short-term face memory.

Adolescent↗

PubMed2005

Acute and chronic estradiol treatments reduce memory deficits induced by transient global ischemia in female rats.

Transient global ischemia induces selective, delayed neuronal death in the hippocampal CA1 and delayed cognitive deficits. Estrogen treatment ameliorates hippocampal injury associated with global ischemia. Although much is known about the impact of estrogen on neuronal survival, relatively little is known about its impact on functional outcome assessed behaviorally. We investigated whether long-term estradiol (21-day pellets implanted 14 days prior to ischemia) or acute estradiol (50 microg infused into the lateral ventricles immediately after ischemia) attenuates ischemia-induced cell loss and improves visual and spatial working memory in ovariectomized female rats. Global ischemia significantly impaired visual and spatial memory, assessed by object recognition and object placement tests at 6-9 days. Global ischemia did not affect locomotion, exploration, or anxiety-related behaviors, assessed by an open-field test at 6 days. Long-term estradiol prevented the ischemia-induced deficit in visual working memory, maintaining normal performance in tests with retention intervals of up to 1 h. Long-term estradiol also prevented ischemia-induced deficits in spatial memory tests with short (1 and 7 min), but not longer (15 min), retention intervals. Acute estradiol significantly improved visual memory assessed with short retention intervals, but did not prevent deficits in spatial memory. Acute estradiol significantly increased the number of surviving CA1 neurons, assessed either at 7 days after ischemia or after the completion of behavioral testing 9 days after ischemia. In contrast, chronic estradiol did not reduce CA1 cell death 9 days after ischemia. Thus, long-term estradiol at near physiological levels and acute estradiol administered after ischemic insult improve functional recovery after global ischemia. These findings have important implications for intervention in the neurological sequellae associated with global ischemia.

Animals↗