Explaining age differences in temporal working memory

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

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

Conserved age-related increases in hippocampal PDE11A4 cause unexpected proteinopathies and cognitive decline of social associative memories

In humans, associative memories are more susceptible to age-related cognitive decline (ARCD) than are recognition memories. Reduced cAMP/cGMP signaling in the hippocampus may contribute to ARCD. Here, we found that both aging and traumatic brain injury-associated dementia increased the expression of the cAMP/cGMP-degrading enzyme phosphodiesterase 11A (PDE11A) in the human hippocampus. Further, age-related increases in hippocampal PDE11A4 mRNA and protein were conserved in mice, as was the increased vulnerability of associative versus recognition memories to ARCD. Interestingly, mouse PDE11A4 protein in the aged ventral hippocampus (VHIPP) ectopically accumulated in the membrane fraction and filamentous structures we term "ghost axons." These age-related increases in expression were driven by reduced exoribonuclease-mediated degradation of PDE11A mRNA and increased PDE11A4-pS117/pS124, the latter of which also drove the punctate accumulation of PDE11A4. In contrast, PDE11A4-pS162 caused dispersal. Importantly, preventing age-related increases in PDE11 expression via genetic deletion protected mice from ARCD of short-term and remote long-term associative memory (aLTM) in the social transmission of food preference assay, albeit at the expense of recent aLTM. Further, mimicking age-related overexpression of PDE11A4 in CA1 of old KO mice caused aging-like impairments in CREB function and remote social-but not non-social-LTMs. RNA sequencing and phosphoproteomic analyses of VHIPP identified cGMP-PKG-as opposed to cAMP-PKA-as well as circadian entrainment, glutamatergic/cholinergic synapses, calcium signaling, oxytocin, and retrograde endocannabinoid signaling as mechanisms by which PDE11A deletion protects against ARCD. Together, these data suggest that PDE11A4 proteinopathies acutely impair signaling in the aged brain and contribute to ARCD of social memories.

Strategic encoding and retrieval processes in verbal recall among middle-aged and older adults

The authors used an analysis of individual differences to examine the role of executive control in strategic encoding and retrieval in verbal recall. Participants enrolled in the Louisiana Healthy Aging Study completed measures of working memory (WM), cognitive status, vocabulary, and free recall of words. Indices of clustering in free recall were calculated to permit inferences on strategic encoding and retrieval processes. We hypothesized that WM would be more strongly associated with strategic encoding and retrieval metrics than vocabulary based on the assumption that successful remembering requires executive control in WM. Regression analyses, together with a variance portioning procedure, confirmed that WM had comparable levels of unique and shared variance with the strategic encoding and retrieval metrics, and both exceeded vocabulary. Theoretical and clinical implications of these data are considered, with the suggestion of future research in lifespan samples as opposed to exclusively young adult or older adult samples.

Adenoviral TMBIM6 vector attenuates ER-stress-induced apoptosis in a neonatal hypoxic-ischemic rat model

Endoplasmic reticulum (ER) stress is a major pathology encountered after hypoxic-ischemic (HI) injury. Accumulation of unfolded proteins triggers the unfolded protein response (UPR), resulting in the activation of pro-apoptotic cascades that lead to cell death. Here, we identified Bax inhibitor 1 (BI-1), an evolutionarily conserved protein encoded by the transmembrane BAX inhibitor motif-containing 6 (TMBIM6) gene, as a novel modulator of ER-stress-induced apoptosis after HI brain injury in a neonatal rat pup. The main objective of our study was to overexpress BI-1, via viral-mediated gene delivery of human adenoviral-TMBIM6 (Ad-TMBIM6) vector, to investigate its anti-apoptotic effects as well as to elucidate its signaling pathways in an in vivo neonatal HI rat model and in vitro oxygen-glucose deprivation (OGD) model. Ten-day-old unsexed Sprague Dawley rat pups underwent right common carotid artery ligation followed by 1.5 h of hypoxia. Rat pups injected with Ad-TMBIM6 vector, 48 h pre-HI, showed a reduction in relative infarcted area size, attenuated neuronal degeneration and improved long-term neurological outcomes. Furthermore, silencing of BI-1 or further activating the IRE1α branch of the UPR, using a CRISPR activation plasmid, was shown to reverse the protective effects of BI-1. Based on our in vivo and in vitro data, the protective effects of BI-1 are mediated via inhibition of IRE1α signaling and in part via inhibition of the second stress sensor receptor, PERK. Overall, this study showed a novel role for BI-1 and ER stress in the pathophysiology of HI and could provide a basis for BI-1 as a potential therapeutic target.

Viral-mediated gene delivery of TMBIM6 protects the neonatal brain via disruption of NPR-CYP complex coupled with upregulation of Nrf-2 post-HI

BACKGROUND

Oxidative stress, inflammation, and endoplasmic reticulum (ER) stress play a major role in the pathogenesis of neonatal hypoxic-ischemic (HI) injury. ER stress results in the accumulation of unfolded proteins that trigger the NADPH-P450 reductase (NPR) and the microsomal monooxygenase system which is composed of cytochrome P450 members (CYP) generating reactive oxygen species (ROS) as well as the release of inflammatory cytokines. We explored the role of Bax Inhibitor-1 (BI-1) protein, encoded by the Transmembrane Bax inhibitor Motif Containing 6 (TMBIM6) gene, in protection from ER stress after HI brain injury. BI-1 may attenuate ER stress-induced ROS production and release of inflammatory mediators via (1) disruption of the NPR-CYP complex and (2) upregulation of Nrf-2, a redox-sensitive transcription factor, thus promoting an increase in anti-oxidant enzymes to inhibit ROS production. The main objective of our study is to evaluate BI-1's inhibitory effects on ROS production and inflammation by overexpressing BI-1 in 10-day-old rat pups.

METHODS

Ten-day-old (P10) unsexed Sprague-Dawley rat pups underwent right common carotid artery ligation, followed by 1.5 h of hypoxia. To overexpress BI-1, rat pups were intracerebroventricularly (icv) injected at 48 h pre-HI with the human adenoviral vector-TMBIM6 (Ad-TMBIM6). BI-1 and Nrf-2 silencing were achieved by icv injection at 48 h pre-HI using siRNA to elucidate the potential mechanism. Percent infarcted area, immunofluorescent staining, DHE staining, western blot, and long-term neurobehavior assessments were performed.

RESULTS

Overexpression of BI-1 significantly reduced the percent infarcted area and improved long-term neurobehavioral outcomes. BI-1's mediated protection was observed to be via inhibition of P4502E1, a major contributor to ROS generation and upregulation of pNrf-2 and HO-1, which correlated with a decrease in ROS and inflammatory markers. This effect was reversed when BI-1 or Nrf-2 were inhibited.

CONCLUSIONS

Overexpression of BI-1 increased the production of antioxidant enzymes and attenuated inflammation by destabilizing the complex responsible for ROS production. BI-1's multimodal role in inhibiting P4502E1, together with upregulating Nrf-2, makes it a promising therapeutic target.

The neural correlates of spatial and object working memory in elderly and Parkinson's disease subjects

This fMRI study deals with the neural correlates of spatial and objects working memory (SWM and OWM) in elderly subjects (ESs) and idiopathic Parkinson's disease (IPD). Normal aging and IPD can be associated with a WM decline. In IPD population, some studies reported similar SWM and OWM deficits; others reported a greater SWM than OWM impairment. In the present fMRI research, we investigated whether compensated IPD patients and elderly subjects with comparable performance during the execution of SWM and OWM tasks would present differences in WM-related brain activations. We found that the two groups recruited a prevalent left frontoparietal network when performing the SWM task and a bilateral network during OWM task execution. More specifically, the ESs showed bilateral frontal and subcortical activations in SWM, at difference with the IPD patients who showed a strict left lateralized network, consistent with frontostriatal degeneration in IPD. The overall brain activation in the IPD group was more extended as number of voxels with respect to ESs, suggesting underlying compensatory mechanisms. In conclusion, notwithstanding comparable WM performance, the two groups showed consistencies and differences in the WM activated networks. The latter underline the compensatory processes of normal typical and pathological aging.

Anti-neutrophil antibody enhances the neuroprotective effects of G-CSF by decreasing number of neutrophils in hypoxic ischemic neonatal rat model

OBJECTIVES

Neonatal hypoxia ischemia (HI) is an injury that can lead to neurological impairments such as behavioral and learning disabilities. Granulocyte-colony stimulating factor (G-CSF) has been demonstrated to be neuroprotective in ischemic stroke however it has also been shown to induce neutrophilia, ultimately exacerbating neuronal injury. Our hypothesis is that coadministration of anti-neutrophil antibody (Ab) with G-CSF will decrease blood neutrophil counts thereby reducing infarct volume and improving neurological function post HI brain injury.

METHODS

Rat pups were subjected to unilateral carotid artery ligation followed by 2.5h of hypoxia. Animals were randomly assigned to five groups: Sham (n=15), vehicle (HI, n=15), HI with G-CSF treatment (n=15), HI with G-CSF+Ab treatment (n=15), and HI with Ab treatment (n=15). Ab (325μg/kg) was administered intraperitoneally while G-CSF (50μg/kg) was administered subcutaneously 1h post HI followed by daily injections for 3 consecutive days. Animals were euthanized at 96h post HI for blood neutrophil counts and brain infarct volume measurements as well as at 5weeks for neurological function testing and brain weight measurements. Lung and spleen weights at both time points were further analyzed.

RESULTS

The G-CSF treatment group showed tendencies to reduce infarct volume and improve neurological function while significantly increasing neutrophil counts. On the other hand, the G-CSF+Ab group significantly reduced infarct volume, improved neurological function and decreased neutrophil counts. The Ab alone group showed reversal of the neuroprotective effects of the G-CSF+Ab group. No significant differences were found in peripheral organ weights between groups.

CONCLUSION

Our data suggest that coadministration of G-CSF with Ab not only prevented brain atrophy but also significantly improved neurological function by decreasing blood neutrophil counts. Hence the neuroprotective effects of G-CSF may be further enhanced if neutrophilia is avoided.

The role of reduced working memory storage and processing resources in the associative memory deficit of older adults: simulation studies with younger adults

Previous research indicates that relative to younger adults, older adults show a larger decline in long-term memory (LTM) for associations than for the components that make up these associations. The purpose of the present study was to investigate whether we can impair associative memory performance in young adults by reducing their working memory (WM) resources, hence providing potential clues regarding the underlying causes of the associative memory deficit in older adults. With two experiments, we investigated whether we can reduce younger adults' long-term associative memory using secondary tasks in which either storage or processing WM loads were manipulated, while participants learned name-face pairs and then remembered the names, the faces, and the name-face associations. Results show that reducing either the storage or the processing resources of WM produced performance patterns of an associative long-term memory deficit in young adults. Furthermore, younger adults' associative memory deficit was a function of their performance on a working memory span task. These results indicate that one potential reason older adults have an associative deficit is a reduction in their WM resources but further research is needed to assess the mechanisms involved in age-related associative memory deficits.

Representational pseudoneglect: a review

Pseudoneglect, the tendency to be biased towards the left-hand side of space, is a robust and consistent behavioural observation best demonstrated on the task of visuospatial line bisection, where participants are asked to centrally bisect visually presented horizontal lines at the perceived centre. A number of studies have revealed that a representational form of pseudoneglect exists, occurring when participants are asked to either mentally represent a stimulus or explore a stimulus using touch in the complete absence of direct visuospatial processing. Despite the growing number of studies that have demonstrated representational pseudoneglect there exists no current and comprehensive review of these findings and no discussion of a theoretical framework into which these findings may fall. An important gap in the current representational pseudoneglect literature is a discussion of the developmental trajectory of the bias. The focus of the current review is to outline studies that have observed representational pseudoneglect in healthy participants, consider a theoretical framework for these observations, and address the impact of lifespan factors such as cognitive ageing on the phenomenon.

Cerebellar vermis size and cognitive ability in community-dwelling elderly men

The cerebellum participates in multiple cognitive functions, including those that are sensitive to decline with aging, and is also vulnerable to atrophy with aging. However, few studies have examined structure-function relationships in older adults. We measured the cross-sectional area of four areas of the cerebellar vermis in 45 community-dwelling men aged 71-76, and correlated this with individual cognitive test scores and two cognitive factors derived from principal components analysis. Two out of the four areas showed positive correlations; vermis area 4 (lobules VIII-X) correlated at r = 0.47 (p = 0.001) with a general cognitive factor accounting for almost half of the cognitive test variance. These findings support the hypothesis that variations in cerebellar structure are associated with cognitive ability in older adults.

Working memory in the oldest-old: evidence from output serial position curves

In the present study, we examined adult age differences in short-term and working memory performance in middle-aged (45-64 years), young-old (65-74 years), old-old (75-89 years), and oldest-old adults (90 years and over) in the Louisiana Healthy Aging Study. Previous research suggests that measures of working memory are more sensitive to age effects than are simple tests of short-term memory Bopp and Verhaeghen (Journal of Gerontology: Psychological Sciences 60:223-233, 2005), Myerson, Emery, White, and Hale, (Aging, Neuropsychology, and Cognition 10:20-27, 2003). To test this hypothesis, we examined output serial position curves of recall data from three span tasks: forward and backward digit span and size judgment span. Participants' recall patterns in the size judgment span task revealed that the two oldest groups of adults showed the largest decreases in recall performance across output serial positions, but did not differ significantly from each other. Correlation analyses indicated the strongest negative correlation with age occurred with the size judgment span task. Implications of these findings for understanding strategic processing abilities in late life are discussed.

Khat use is associated with impaired working memory and cognitive flexibility

Rationale

Khat consumption has increased during the last decades in Eastern Africa and has become a global phenomenon spreading to ethnic communities in the rest of the world, such as The Netherlands, United Kingdom, Canada, and the United States. Very little is known, however, about the relation between khat use and cognitive control functions in khat users.

Objective

We studied whether khat use is associated with changes in working memory (WM) and cognitive flexibility, two central cognitive control functions.

Methods

Khat users and khat-free controls were matched in terms of sex, ethnicity, age, alcohol and cannabis consumption, and IQ (Raven's progressive matrices). Groups were tested on cognitive flexibility, as measured by a Global-Local task, and on WM using an N-back task.

Result

Khat users performed significantly worse than controls on tasks tapping into cognitive flexibility as well as monitoring of information in WM.

Conclusions

The present findings suggest that khat use impairs both cognitive flexibility and the updating of information in WM. The inability to monitor information in WM and to adjust behavior rapidly and flexibly may have repercussions for daily life activities.

How arousal affects younger and older adults' memory binding

A number of recent studies have shown that associative memory for within-item features is enhanced for emotionally arousing items, whereas arousal-enhanced binding is not seen for associations between distinct items (for a review, see Mather, 2007, Perspectives on Psychological Science, 2, 33-52). The costs and benefits of arousal in memory binding have been examined for younger adults but not for older adults. The present experiment examined whether arousal would enhance younger and older adults' within-item and between-item memory binding. The results revealed that arousal improved younger adults' within-item memory binding but not that of older adults. Arousal worsened both groups' between-item memory binding.

The effects of aging on memory for sequentially presented objects in rats

The current study investigated memory for sequentially presented objects in young rats 6 months old (n = 12) and aged rats 24 months old (n = 12). Rats were tested on a task involving three exploratory trials and one probe test. During the exploratory trials, the rat explored a set of three sequentially presented object pairs (A-A, B-B, and C-C) for 5 min per pair with a 3-min delay between each pair. Following the exploratory trials, a probe test was conducted where the rat was presented simultaneously with one object from the first exploratory trial (A) and one object from the third exploratory trial (C). Results from the exploratory trials showed no significant age-related differences in exploration, indicating that 24-month-old rats explored the object pairs as much as 6-month-old rats. The probe test demonstrated that 6-month-old rats spent significantly more time exploring object A compared to object C, indicating that young rats show intact temporal order memory for the exploratory trial objects. However, 24-month-old rats showed no preference for object A and spent a relatively equal amount of time exploring objects A and C. The results suggest that temporal order memory declines as a result of age-related changes in the rodent brain. The findings also may reflect differences in attraction to objects with different memory strengths. Since age-related differences were not detected during the exploratory trials, age-related differences on the probe trial were not due solely to decreased exploration, motivation, or locomotion.

Transfer of computer-based training to simulated driving in older adults

As the population of many industrialized countries ages, the number of older drivers on the roads increases. Statistics show that older drivers are at increased risk for involvement in fatal accidents. One explanation for this is the cognitive and motor declines associated with the aging process. As we age, performance on attention, memory and motor control tasks, three important components of driving, declines. In the present study we examined the relationship between performance on component cognitive tasks and the influence of training on these tasks on the simulated driving performance of older adults. More specifically, we assessed performance on and trained older adults on single and dual tasks of attention, working memory and manual control. Regression analyses demonstrated that performance on the single and dual cognitive tasks and improvements in these computer-based tasks with training were predictive of improvements in driving simulator performance across the course of the study. These data suggest that relatively simple single and dual computer-based tasks and modest amounts of training on these tasks can improve driving performance in older adults, thereby extending functional independence.

Recreational cocaine polydrug use impairs cognitive flexibility but not working memory

RATIONALE

Chronic use of cocaine is associated with dysfunctions in frontal brain regions and dopamine D2 receptors, with poorer mental flexibility and a reduced ability to inhibit manual and attentional responses. Little is known, however, about cognitive impairments in the upcoming type of recreational cocaine polydrug user (1-4 g monthly consumption).

OBJECTIVE

We studied whether recreational cocaine polydrug users, who do not meet the criteria for abuse or dependence, showed impairments in working memory (WM) and cognitive flexibility.

METHODS

Controls and recreational cocaine polydrug users (who abstained from cocaine and other substances more than 1 week) were matched by sex, age, alcohol consumption, and IQ (Raven's Standard Progressive Matrices). Groups were tested by using two cognitive tasks measuring cognitive flexibility and three tasks investigating the maintenance and monitoring of information in WM.

RESULTS

Recreational cocaine polydrug users performed significantly worse than controls on tasks tapping cognitive flexibility, but show comparable performance in the active maintenance and monitoring of information in WM.

CONCLUSIONS

The findings suggest that recreational use of cocaine selectively impairs cognitive flexibility but not the maintenance of information in WM. The inability to adjust behavior rapidly and flexibly may have repercussions for daily life activities.

Age-related differences in immediate serial recall: dissociating chunk formation and capacity

We assessed the contribution of two hypothesized mechanisms to impaired memory performance of older adults in an immediate serial recall task: decreased temporary information storage in a capacity-limited mechanism, such as the focus of attention, and a deficit in binding together different components into cohesive chunks. Using a method in which paired associations between words were taught at varying levels to allow an identification of multiword chunks (Cowan, Chen, & Rouder, 2004), we found that older adults recalled considerably fewer chunks and, on average, smaller chunks than did young adults. Their performance was fairly well simulated by dividing attention in younger adults, unlike what has been found for long-term associative learning. Paired-associate knowledge may be used in an implicit manner in serial recall, given that younger adults under divided attention and older adults use it well despite the relatively small chunk capacities displayed by these groups.