Working memory capacity links cognitive reserve with long-term memory in moderate to severe TBI: a translational approach

Lower cognitive reserve is related to worse working memory performance in older adults after mTBI. An ERP study

OBJECTIVE

Older adults (OA) after mild traumatic brain injury (mTBI) have a high risk of developing persistent post-injury cognitive impairments. Lower pre-morbid cognitive reserve (CR) is increasingly investigated as a risk factor for cognitive dysfunction in OA. However, how CR protects against effects of mTBI at the brain level remains largely understudied.

METHODS

We examined 22 OA who sustained mTBI (mean 67.69 years, SD 5.11) in the sub-acute phase and 15 age- and CR-matched healthy OA (mean 68 years, SD 5.55) performing a three-level visual N-back task using electroencephalography. We calculated inverse efficiency scores of performance from accuracy and reaction times. Event-related potentials served as neurocognitive correlates of attentional (P2) and working memory (P3) processing.

RESULTS

Overall, mTBI OA performed worse than healthy OA (p = 0.031). Lower CR generally decreased performance (p < 0.001). Furthermore, with increasing task difficulty, task performance was more affected by CR (p = 0.004). At the brain level, P2 amplitude was lower in mTBI OA than in healthy OA (p = 0.05). There was no clear effect of CR on P2 or P3 measures.

CONCLUSION

As mTBI OA with lower CR performed worse on a working-memory task, lower CR may be a risk factor for worse recovery after mTBI in this group.

Which intellectual activities are related to cognitive reserve? Introduction and testing a three-dimensional model

BACKGROUND

A common belief among people and some researchers is that keeping yourself mentally active may decrease the risk of dementia. Over the past years, despite widespread efforts to identify proxies for protecting cognitive reserve against age-related changes, it is still not clear what type of intellectual activity would be beneficial for cognitive reserve. To fill this gap, we propose a three-dimensional model of intellectual activity. According to this conceptual model, intellectual activities could be distinguished based on their locations in a three-dimensions space, including; (1) Activation: active vs. passive, (2) Novelty: novel vs. familiar, and (3) Productivity: productive vs. receptive. We assumed that the activities that are categorized as more active, novel, and productive could be considered as a cognitive reserve proxy.

METHODS

To test this hypothesis, a sample of 237 participants older than 50 years (Mage = 58.76 ± 6.66; 63.7% women) was recruited to take part in the study. Episodic, semantic and working memory were assessed with computerized battery tests (Sepidar) and a self-report questionnaire was used to assess intellectual activities. Activities were categorized in terms of; (1) passive, familiar, and receptive activities (radio/watching TV), (2) active, familiar, and receptive activities (solving crosswords), (3) active, novel, and receptive activities (reading), and (4) active, novel, and productive activities (writing).

RESULTS

The results indicated that writing moderates the effect of age on episodic and semantic memory. Reading only moderates the effect of age on semantic memory, and radio/watching TV and solving crosswords do not play a role in moderation analysis.

CONCLUSIONS

Our finding suggests that intellectual activities have different moderating effects on the relationships between age and memory performance. Individuals with high levels of participation in novel and productive activities over the life course are less likely to clinically demonstrate cognitive impairments. Our results support the potential benefit of the three-dimensional model to provide a better insight into the complex role of intellectual activities in cognitive reserve, particularly for older adults. Further research is needed to evaluate the efficacy and the benefits of the model.

The role of cognitive reserve in traumatic brain injury: a systematic review of observational studies

OBJECTIVE

Evaluate the role of cognitive reserve (CR) on cognitive and physical sequelae in traumatic brain injury (TBI).

METHODS

A comprehensive search strategy was conducted in four databases in English and Spanish in the last 12 years (2011-2023). Inclusion criteria: original cross-sectional and longitudinal studies whose main or secondary objective was to evaluate the effect of CR in adult patients with TBI. PRISMA guidelines were used to report the search and selection method and STROBE checklist was used to evaluate the quality of studies.

RESULTS

Eighteen observational studies were included in this review. Multiple sources of variability were observed: number of patients, time of evolution, severity of the TBI, type of CR proxy, cognitive assessment instrument, etc. However, the most commonly used indicators of CR were premorbid IQ and educational attainment. A positive and consistent association between CR and performance on cognitive tests after injury was found.

CONCLUSIONS

CR has a consistent positive effect on cognition and on some other aspects of recovery in traumatic brain injury. In future studies, it will be necessary to promote the use of CR indices based on various indicators and explore the effects of CR on other aspects related to the recovery of brain trauma.

A Slip Between the Brain and the Lip: Working Memory and Cognitive-Communication Disorders

The relationship between working memory and speech has been a topic of intense research interest and investigation for many years. Memory studies have found that the active processing of working memory is required for language comprehension and speech production. Though there are studies that discuss the capacity of working memory, the processing of verbal stimuli into verbal memory remains unclear. Therefore, it is essential to understand the functioning of the working memory and how it processes verbal information. As working memory is intricately linked with communication, any deficits in working memory could cause communication disorders. Also, the disruption in the storage and retrieval of verbal memory could cause a disturbance in the speech pattern. To this point, this review elaborates on the active processing of working memory and its role in communication. Further, by studying the deficits in working memory that could cause cognitive-communication disorders such as apraxia of speech, dementia, and dysarthria, this article highlights the importance of verbal memory in speech.

Cognitive Reserve in Isolated Rapid Eye-Movement Sleep Behavior Disorder

Isolated rapid-eye-movement sleep behaviour disorder (RBD) is considered the prodromal stage of α-synucleinopathies (e.g., Parkinson's disease and dementia with Lewy bodies); however, iRBD patients show a wide variety in the progression timing (5-15 years). The model of cognitive reserve (CR) might contribute to explaining this phenomenon. Our exploratory study aimed to evaluate, for the first time, the impact of CR level on cognitive performance in polysomnography-confirmed iRBD patients. Fifty-five iRBD patients (mean age ± SD: 66.38 ± 7.51; M/F 44/11) underwent clinical and neuropsychological evaluations at the time of diagnosis. The CR Index questionnaire was part of the clinical assessment. We found that iRBD patients with high levels of CR showed: (i) the lowest percentage of mild cognitive impairment (10%), and (ii) the best performance in visuo-constructive and verbal memory functions (i.e., the recall of the Rey-Osterrieth complex figure test). Our results suggest that CR might help iRBD patients better cope with the cognitive decline related to the neurodegenerative process, providing the first preliminary findings supporting CR as a possible protective factor in this condition. This might pave the way for future longitudinal studies to evaluate the role of CR as a modulating factor in the timing of iRBD conversion and cognitive deterioration development.

Abnormal Dorsal Caudate Activation Mediated Impaired Cognitive Flexibility in Mild Traumatic Brain Injury

BACKGROUND

Mild traumatic brain injury (mTBI) is an important but less recognized public health concern. Previous studies have demonstrated that patients with mTBI have impaired executive function, which disrupts the performance of daily activities. Few studies have investigated neural mechanisms of cognitive flexibility in mTBI patients using objective tools such as the psychological experiment paradigm. Here, we aimed to examine neural correlates of cognitive flexibility in mTBI.

METHODS

Sixteen mTBI patients and seventeen matched healthy controls (HCs) underwent functional MRI during a rule-based task-switching experimental paradigm. Linear models were used to obtain within-group activation maps and areas of differential activation between the groups. In addition, we conducted mediation analyses to evaluate the indirect effect of abnormal dorsal caudate activation on the association between information processing speed and cognitive flexibility in mTBI.

RESULTS

mTBI patients exhibited significantly longer reaction time in the task switching (TS) condition compared to HCs, reflecting impaired cognitive flexibility. In addition, the patients showed reduced activation in the dorsal caudate (dCau), anterior cingulate cortex, and other frontal regions during the TS condition. Mediation analysis revealed that the reduced dCau activation had a significant effect on the relationship between information processing speed and cognitive flexibility in mTBI.

CONCLUSIONS

Abnormal dorsal caudate activation in mTBI mediates impaired cognitive flexibility, which indicated dorsal caudate might be playing a vital role in the cognitive flexibility of mTBI patients. These findings highlight an alternative target for clinical interventions for the improvement of cognitive functions in mTBI.

Effects of Cognitive Reserve on Cognition in Individuals With Central Nervous System Disease

Cognitive reserve (CR) has been proposed to account for functional outcome differences in brain pathology and its clinical manifestations. The purpose of our paper is to systematically review the effects of CR on cognitive outcomes in individuals with neurodegenerative and structural CNS diseases. We performed a systematic search of PubMed, CINAHL (Cumulative Index to Nursing and Allied Health Literature), and PsychInfo using the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Seventeen studies met the predetermined inclusion criteria and were selected for review. Education level was the most commonly used measure for CR, and various neuropsychological tests were used to measure cognitive outcomes. Regardless of the CNS disease of the individuals, almost all of the studies reported a positive association between CR and cognitive outcomes when they were evaluated cross-sectionally. However, when evaluated longitudinally, CR had either no effect on, or a negative association with, cognitive outcomes. Based on studies across a broad spectrum of CNS diseases, our findings suggest that CR may serve as a predictor of cognitive outcomes in individuals with CNS diseases. However, studies to date are limited by a lack of imaging analyses and standardized assessment strategies. The ability to use a standardized measure to assess the longitudinal effects of CR may allow for the development of more targeted treatment methods, resulting in improved disease outcomes for individuals.

Metformin reduces neuroinflammation and improves cognitive functions after traumatic brain injury

Within the brain, traumatic brain injury (TBI) alters synaptic plasticity and increases neuroinflammation and neuronal death. Yet, there lacks effective TBI treatments providing pleiotropic beneficial effects on these diverse cellular processes necessary for functional recovery. Here, we show the diabetes drug, metformin, significantly improves cognitive functions after controlled cortical impact (CCI) injury in mice, showing improved spatial learning and nest building. Furthermore, injured animals treated with metformin exhibit increased ramification of microglia processes, indicating reduced neuroinflammation. Finally, metformin treatment in vitro increased neuronal activation of partitioning defective 1 (Par1), a family of Ser/Thr kinases playing a key role in synaptic plasticity and neuroinflammation. These results suggest metformin is a promising therapeutic agent for targeting multiple cellular processes necessary for functional TBI recovery.

Bilingualism contributes to reserve and working memory efficiency: Evidence from structural and functional neuroimaging

This study compared brain and behavioral outcomes for monolingual and bilingual older adults who reported no cognitive or memory problems on three types of memory that typically decline in older age, namely, working memory (measured by n-back), item, and associative recognition. The results showed that bilinguals were faster on the two-back working memory task than monolinguals but used a set of frontostriatal regions less than monolinguals. There was no group difference on an item/associative recognition task. In brain structure, gray matter volume and white matter integrity (fractional anisotropy) were generally lower in bilinguals than in monolinguals, but bilinguals had better white matter integrity than monolinguals in the bilateral superior corona radiata and better gray matter density in the left inferior temporal gyrus. These regions may help preserve bilinguals' executive functions despite generally more significant atrophy throughout the brain than monolinguals in that these structures contribute to efficient communication between executive frontal regions and subcortical motor regions, and perceptual pathways. Reliable negative correlations between brain structure and age were only observed in bilinguals, and to the extent that bilinguals (but not monolinguals) had better brain structure, their performance was enhanced. Collectively, the findings provide evidence for reserve in bilingual older adults.

Loneliness, Sense of Control, and Risk of Dementia in Healthy Older Adults: A Moderated Mediation Analysis

Objectives: Despite the rising prevalence of dementia, little research has been conducted to identify modifiable psychological factors that alleviate the risk of dementia in older adults and the underlying mechanisms. Given that loneliness is, in part, concomitant with a weakened sense of control, we examined whether sense of control would mediate the relation between loneliness and dementia risk. Further, considering that working -memory capacity is a critical cognitive resource that serves as a buffer against age-related cognitive decline, we examined a second-order moderated mediational model whereby working-memory capacity moderates the relation between control beliefs and dementia risk in older adults.

METHODS

We administered a series of measures to older community-dwelling adults (ages 60-93; N = 69), including the participant-rated AD8 to assess the risk of dementia. Using the PROCESS macro, we examined the moderated mediation model for the relation between loneliness, sense of control, and dementia risk.

RESULTS

We found that sense of control significantly mediated the relation between loneliness and risk of dementia. Moreover, the indirect effect of loneliness on dementia risk via lowered sense of control was significant only in individuals with poorer working-memory capacity. Notably, these findings held true when important covariates were controlled for.

CONCLUSIONS

Our findings underscore the critical role of control beliefs and working memory in protecting against dementia risk.

CLINICAL IMPLICATIONS

Our findings have implications for intervention programs that target alleviating dementia risk and promoting healthy aging in older adults by improving socioemotional health and cognitive functioning.

Validity and reliability of "Cognitive Reserve Index Questionnaire" for the Turkish Population

BACKGROUND

Cognitive reserve (CR) is the ability to counteract brain damage through differential recruitment of brain networks. Besides, it has also been observed that lifetime intellectual enriching skills reduce the effect of disease burden on cognitive status. The Cognitive Reserve Index questionnaire (CRIq), which is a method for the quantitative measurement and comprehensive evaluation of the CR, that individuals have accumulated throughout their lifetimes. The present study aimed to adapt CRIq to the Turkish population.

METHODS

CRIq is a 20-item questionnaire consisting of 3 sub-scales (CRI-Education, CRI- Working Activity, CRI-Leisure Time). 271 females and 228 males, a total of 499 healthy volunteers participated in the study (mean age: 39.54±14.05, mean education years 13.14±4.84). Participants were evaluated with the "Brief International Cognitive Assessment for Multiple Sclerosis (BICAMS)" and CRIq was applied. BICAMS was used to determine the validity of the CRIq. To determine the reliability, the questionnaire was applied again two weeks after the first application. Internal consistency and test-retest reliability were measured for reliability analysis. Independent sample t-test was conducted to observe the difference between genders.

RESULTS

The Cronbach alpha coefficient of the questionnaire was 0.78, and the reliability of the questionnaire was acceptable. The findings showed that inter-rater reliability was quite high (ICC:0.95, 95% CI=1.000, n=36). The correlation between the first and second application of the questionnaire was found to be acceptable for both the sub-scales and the whole questionnaire. The highest CRIq scores were shown for young adults in CRI-Education and CRI-LeisureTime, for the middle-aged in CRIq-WorkingActivity, no significant differences in total CRIq scores. The males scored significantly higher in CRIq total scores than females, but there was not a significant difference in CRI-LeisureTime between genders.

CONCLUSION

The Turkish version of CRIq was found to be a valid and reliable method for evaluating cognitive reserve in healthy individuals.

The potential role of leukoaraiosis in remodeling the brain network to buffer cognitive decline: a Leukoaraiosis And Disability study from Alzheimer's Disease Neuroimaging Initiative

Background

Leukoaraiosis (LA) is a phenomenon of the brain that is often observed in elderly people. However, little is known about the role of LA in cognitive impairment in neurodegeneration and disease. This cross-sectional, retrospective Leukoaraiosis And Disability (LADIS) study aimed to characterize the relationship between brain white matter connectivity properties with LA ratings in patients with Alzheimer's disease (AD) as compared with age-matched cognitively normal controls.

Methods

Patients with AD (n=76) and elderly individuals with normal cognitive (NC) function (n=82) were classified into 3 groups, LA1, LA2, and LA3, according to the rating of their white matter changes (WMCs). Diffusion tensor imaging (DTI) data were analyzed by quantifying and comparing the white matter connectivity properties and gray matter (GM) volume of brain regions of interest (ROIs).

Results

The rich-club network properties in the AD LA1 and LA2 groups showed significant patterns of disrupted peripheral regions and reduced connectivity compared to those in the NC LA1 and LA2 groups, respectively. However, the rich-club network properties in the AD LA3 group showed similar patterns of disrupted peripheral regions and reduced connectivity compared to those in the NC LA3 group, despite there being significant hippocampal and amygdala atrophic differences between AD patients and NC elders. Compared to the NC LA1 group, the characteristic path length of white matter fiber connectivity in the NC LA3 group was significantly increased, and the brain's global efficiency, clustering coefficient, and network connectivity strength were significantly reduced (P<0.05, respectively). However, no significant differences (P>0.05) were observed in characteristic path length, reduced global efficiency, or the clustering coefficient between the NC LA3 and AD LA1 groups, or between the NC LA3 and AD LA2 groups.

Conclusions

Our findings offer some insights into a potential role of LA in cognitive impairment that may predict the development of disability in older adults. The occurrence of LA, an intermediate degenerative change, during neurodegeneration and disease may potentially lead to the remodeling of the brain network through brain plasticity. LA, therefore, representing a possible compensatory mechanism to buffer cognitive decline.

Attentional flexibility and prioritization improves long-term memory

Recent evidence suggests the focus of attention (FoA) is a flexible resource within working memory (WM) used to temporarily maintain some information in a highly accessible state. This flexibility comes at the expense of other representations, demonstrating a resource trade-off in WM maintenance. The present experiments evaluate how flexibility within the FoA impacts long-term memory (LTM) for semantically meaningful information. A WM probe-recognition task was used in which two items were presented in black and a single item was presented in red. To encourage the prioritization and uninterrupted preferential maintenance of specific items, a process we call online refreshing, the red item was associated with a greater point-reward value than were the black items. This WM task was followed by a surprise delayed LTM test. In Experiment 1, the FoA flexibly adjusted to maintain non-recent semantic information with evidence for a resource trade-off across list positions. Flexibility also directly improved LTM. In Experiment 2, reward value was equated across red and black items to evaluate whether an alternative explanation, distinctiveness of encoding, could account for the LTM findings. When reward value was equated, the cued item did not encourage flexible orienting of the FoA toward non-recent items and there was no benefit of the distinct red item on LTM performance. While supportive of past research, these data further demonstrate that semantic information can be flexibly prioritized at the expense of other list positions and that this is directly tied to improvements in LTM.

Cognitive reserve and working memory in cognitive performance of adults with subjective cognitive complaints: longitudinal structural equation modeling

OBJECTIVE

To study the influence of cognitive reserve (CR) on cognitive performance of individuals with subjective cognitive complaints (SCCs) within a period of 36 months.

DESIGN

We used a general linear model repeated measures procedure to analyze the differences in performance between three assessments. We used a longitudinal structural equation modeling to analyze the relationship between CR and cognitive performance at baseline and at two follow-up assessments.

SETTING

Participants with SCCs were recruited and assessed in primary care health centers.

PARTICIPANTS

A total of 212 participants older than 50 years with SCCs.

MEASUREMENTS

Cognitive reserve data were collected with an ad hoc questionnaire administered to the subjects in an interview. General cognitive performance (GCP), episodic memory (EM), and working memory (WM) have been evaluated. The Mini-Mental State Examination and the total score of Spanish version of the Cambridge Cognitive Examination evaluated the GCP. Episodic memory was assessed with the Spanish version of the California Verbal Learning. Working memory was evaluated by the counting span task and the listening span task.

RESULTS

The satisfactory fit of the proposed model confirmed the direct effects of CR on WM and GCP at baseline, as well as indirect effects on EM and WM at first and second follow-up. Indirect effects of CR on other cognitive constructs via WM were observed over time.

CONCLUSION

The proposed model is useful for measuring the influence of CR on cognitive performance over time. Cognitive response acquired throughout life may influence cognitive performance in old age and prevent cognitive deterioration, thus increasing processing resources via WM.

Cognitive Reserve as an Emerging Concept in Stroke Recovery

Stroke is a leading cause of death and disability. It is a complex and largely heterogeneous condition. Prognosis for variations in impairment and recovery following stroke continues to be challenging and inaccurate, highlighting the need to examine the influence of other currently unknown variables to better predict and understand interindividual differences in stroke impairment and recovery. The concept of "cognitive reserve," a feature of brain function said to moderate the relationship between brain pathology and clinical outcomes, might provide a partial explanation. This review discusses the potential significance of cognitive reserve in the context of stroke, with reference to reduced burden of disability poststroke, health promotion, intervention and secondary prevention of cognitive impairment, ease and challenges of translation into clinical practice, prognosis and prediction of recovery, and clinical decisions and trial stratification. Discussions from the review aim to encourage stroke clinicians and researchers to better consider the role of premorbid, lifestyle-related variables, such as cognitive reserve, in facilitating successful neurological outcomes and recovery following stroke.

The Association of Cognitive Reserve in Chronic-Phase Functional and Neuropsychological Outcomes Following Traumatic Brain Injury

OBJECTIVE

Examine the association of cognitive reserve (CR) factors (estimated premorbid intelligence quotient [IQ], years of education, and occupational attainment) and traumatic brain injury (TBI) severity with functional and neuropsychological outcomes 1 to 5 years following TBI.

PARTICIPANTS

Patients with mild (N = 58), moderate (N = 25), or severe (N = 17) TBI.

MAIN MEASURES

Cognitive reserve factors (estimated premorbid IQ, years of education, and occupational attainment); neuropsychological test battery; Glasgow Outcome Scale-Extended; Short Form-36 Health Survey.

ANALYSES

Spearman-Brown correlations, linear regression models, and analyses of covariance were used to analyze the relation between CR factors and outcome measures.

RESULTS

Analyses revealed significant relations between estimated premorbid IQ and neuropsychological outcomes (P < .004): California Verbal Learning Test, Wechsler Adult Intelligence Scale-Fourth Edition working memory, Booklet Category Test, Trail Making Test B, and Grooved Pegboard Test. There was also a significant correlation between estimated premorbid IQ and Wechsler Adult Intelligence Scale-Fourth Edition processing speed. Years of education had significant relations with California Verbal Learning Test and Wechsler Adult Intelligence Scale-Fourth Edition working memory and processing speed scores. There were significant differences between TBI severity groups and performance on the Trail Making Test A, Grooved Pegboard Test, and Finger Tapping Test.

CONCLUSIONS

Cognitive reserve factors may be associated with outcomes following TBI. Additional alternatives to TBI severity are needed to help guide rehabilitative planning postinjury.

Structural changes in white matter lesion patients and their correlation with cognitive impairment

BACKGROUND

White matter lesions (WMLs) play a role in cognitive decline and dementia. Little is known about gray matter (GM) changes in WMLs. This study aimed to investigate GM changes in WML patients.

MATERIALS AND METHODS

Correlations between altered structural volume and cognitive assessment scores were investigated. GM and white matter (WM) changes in 23 WML-vascular dementia (VaD) patients, 22 WML-non-dementia vascular cognitive impairment (VCIND) patients, and 23 healthy control (HC) subjects were examined. Gray matter density (GMD) was calculated by measuring local proportions of GM at thousands of homologous cortical locations. WM volume was obtained by fully automated software using voxel-based morphometry (VBM).

RESULTS

Widespread GMD was significantly lower in WML patients compared to control subjects in cortical and subcortical regions (p<0.05). Greatest differences were found in the bilateral anterior cingulate cortex, inferior frontal gyrus, insula, angular gyrus, caudate, precentral gyrus, and right middle temporal gyrus, right thalamus. Secondary region of interest (ROI) analysis indicated significantly greater GMD in the bilateral caudate among WML-VCIND patients (n=22) compared to HCs (p<0.05). There was a significant difference in WM volume between WML patients and control subjects (p<0.05). Greatest differences were located in the genu/body/splenium of the corpus callosum and superior corona radiata L, and posterior corona radiata L. There was a significant association between structural changes and cognitive scores (Montreal Cognitive Assessment [MoCA] score) (p<0.05). There was no significant correlation between structural changes and Mini Mental State Examination (MMSE) scores (p>0.05).

CONCLUSION

GMD and WM volume were changed in WMLs, and the changes were detectable. Correlation between structural changes and cognitive function was promising in understanding the pathological and physiological mechanisms of WMLs.

Comprehension of Legal Language by Adults With and Without Traumatic Brain Injury

OBJECTIVE

To characterize comprehension of written legal language in adults with and without traumatic brain injury (TBI).

PARTICIPANTS

Nineteen adults with moderate-to-severe TBI (11 females) and 21 adults without TBI (13 females), aged 24 to 64 years.

METHODS

Participants completed a multiple-choice assessment of legal-language comprehension, with written stimuli either presented in their original legal form or manipulated to simplify syntax or use more frequently occurring words.

RESULTS

Across stimulus types, TBI group participants were significantly less accurate and slower than comparison peers, with no effect of linguistic manipulation. Working memory and reading fluency test scores correlated with task accuracy and speed in both groups.

CONCLUSIONS

Adults with TBI underperformed their uninjured peers in both accuracy and speed on a task of legal-language comprehension, and these differences were attributable in part to differences in working memory and reading fluency. Results highlight the potential costs of TBI-related communication problems in criminal proceedings and the need to formally evaluate language comprehension in individuals with TBI who are in the criminal justice system.

Effects of Cognitive Reserve on Cognitive Performance in a Follow-Up Study in Older Adults With Subjective Cognitive Complaints. The Role of Working Memory

Objective: Analyze the effects of CR on cognitive performance in adults with subjective cognitive complaints at follow-up. Method: We analyzed the factorial structure of the three constructs defined in cognitive performance (Episodic memory, Working memory, and General cognitive performance) separately to search for evidence of the invariance of the measurement model. We then developed four structural nested models to analyze the relationship between CR and cognitive performance, measured at baseline and after approximately 18 months, in 266 participants older than 50 years with subjective cognitive complaints. Results: The nested models revealed the following main results: direct effects of CR on all cognitive constructs at baseline and also indirect effects on the same constructs at follow-up, and indirect effects of CR on other cognitive constructs at follow-up via working memory at follow-up. Conclusion: The findings show that the proposed model is useful for measuring the influence of CR on cognitive performance in follow-up studies and that CR has a positive influence on cognitive performance at follow-up via working memory. CR may enhance mechanisms of information processing, favoring performance of tasks involving other cognitive constructs in older adults with subjective cognitive complaints.

Granulocyte-colony stimulating factor and umbilical cord blood cell transplantation: Synergistic therapies for the treatment of traumatic brain injury

Traumatic brain injury (TBI) is now characterized as a progressive, degenerative disease and continues to stand as a prevalent cause of death and disability. The pathophysiology of TBI is complex, with a variety of secondary cell death pathways occurring which may persist chronically following the initial cerebral insult. Current therapeutic options for TBI are minimal, with surgical intervention or rehabilitation therapy existing as the only viable treatments. Considering the success of stem-cell therapies in various other neurological diseases, their use has been proposed as a potential potent therapy for patients suffering TBI. Moreover, stem cells are highly amenable to adjunctive use with other therapies, providing an opportunity to overcome the inherent limitations of using a single therapeutic agent. Our research has verified this additive potential by demonstrating the efficacy of co-delivering human umbilical cord blood (hUCB) cells with granulocyte-colony stimulating factor (G-CSF) in a murine model of TBI, providing encouraging results which support the potential of this approach to treat patients suffering from TBI. These findings justify ongoing research toward uncovering the mechanisms which underlie the functional improvements exhibited by hUCB + G-CSF combination therapy, thereby facilitating its safe and effect transition into the clinic. This paper is a review article. Referred literature in this paper has been listed in the reference section. The datasets supporting the conclusions of this article are available online by searching various databases, including PubMed. Some original points in this article come from the laboratory practice in our research center and the authors’ experiences.

Balanced bifrontal transcranial direct current stimulation enhances working memory in adults with high-functioning autism: a sham-controlled crossover study

Background

Working memory (WM) often is impaired in autism spectrum disorder (ASD). Such impairment may underlie core deficits in cognition and social functioning. Transcranial direct current stimulation (tDCS) has been shown to enhance WM in both healthy adults and clinical populations, but its efficacy in ASD is unknown. We predicted that bifrontal tDCS would improve WM performances of adults with high-functioning autism during active stimulation compared to sham stimulation and that such enhancement would generalize to an untrained task.

Methods

Twelve adults with high-functioning ASD engaged in a battery of WM tasks that included backward spatial span, backward digit span, spatial n-back and letter n-back. While engaged, 40 min of 1.5 mA bifrontal stimulation was applied over the left and the right dorsolateral prefrontal cortices (DLPFC). Using a single-blind crossover design, each participant received left anodal/right cathodal stimulation, right anodal/left cathodal stimulation, or sham stimulation, in randomized counterbalanced order on three separate days. Following tDCS, participants again engaged in letter and spatial n-back tasks before taking the Brief Test of Attention (BTA). We used repeated-measures ANOVA to compare overall performance on the WM battery as measured by a composite of z-scores for all five measures. Post hoc ANOVAs, t tests, Friedman’s tests, and Wilcoxon signed-rank tests were used to measure the online and offline effects of tDCS and to assess performances on individual measures.

Results

Compared to sham stimulation, both left DLPFC anodal stimulation (t₁₁ = 5.4, p = 0.0002) and right DLPFC anodal stimulation (t₁₁ = 3.57, p = 0.004) improved overall WM performance. Left anodal stimulation (t₁₁ = 3.9, p = 0.003) and right anodal stimulation (t₁₁ = 2.7, p = 0.019) enhanced performances during stimulation. Enhancement transferred to an untrained task 50 min after right anodal stimulation (z₁₁ = 2.263, p = 0.024). The tasks that showed the largest effects of active stimulation were spatial span backward (z₁₁ = 2.39, p = 0.017) and BTA (z₁₁ = 2.263, p = 0.024).

Conclusions

In adults with high-functioning ASD, active bifrontal tDCS given during WM tasks appears to improve performance. TDCS benefits also transferred to an untrained task completed shortly after stimulation. These results suggest that tDCS can improve WM task performance and could reduce some core deficits of autism.

Trial registration

NCT01602263

Individual Differences in Working Memory Capacity Predicts Responsiveness to Memory Rehabilitation After Traumatic Brain Injury

OBJECTIVE

To explore how individual differences affect rehabilitation outcomes by specifically investigating whether working memory capacity (WMC) can be used as a cognitive marker to identify who will and will not improve from memory rehabilitation.

DESIGN

Post hoc analysis of a randomized controlled clinical trial designed to treat learning and memory impairment after traumatic brain injury (TBI): 2 × 2 between-subjects quasiexperimental design (2 [group: treatment vs control] × 2 [WMC: high vs low]).

SETTING

Nonprofit medical rehabilitation research center.

PARTICIPANTS

Participants (N=65) with moderate to severe TBI with pre- and posttreatment data.

INTERVENTIONS

The treatment group completed 10 cognitive rehabilitation sessions in which subjects were taught a memory strategy focusing on learning to use context and imagery to remember information. The placebo control group engaged in active therapy sessions that did not involve learning the memory strategy.

MAIN OUTCOME MEASURE

Long-term memory percent retention change scores for an unorganized list of words from the California Verbal Learning Test-II.

RESULTS

Group and WMC interacted (P=.008, ηp(2)=.12). High WMC participants showed a benefit from treatment compared with low WMC participants. Individual differences in WMC accounted for 45% of the variance in whether participants with TBI in the treatment group benefited from applying the compensatory treatment strategy to learn unorganized information.

CONCLUSIONS

Individuals with higher WMC showed a significantly greater rehabilitation benefit when applying the compensatory strategy to learn unorganized information. WMC is a useful cognitive marker for identifying participants with TBI who respond to memory rehabilitation with the modified Story Memory Technique.