Intraindividual Variability in Inhibition and Prospective Memory in Healthy Older Adults: Insights from Response Regularity and Rapidity

Analysis of modulations of mental fatigue on intra-individual variability from single-trial event related potentials

BACKGROUND

Intra-individual variability (IIV), a measure of variance within an individual's performance, has been demonstrated as metrics of brain responses for neural functionality. However, how mental fatigue modulates IIV remains unclear. Consequently, the development of robust mental fatigue detection methods at the single-trial level is challenging.

NEW METHODS

Based on a long-duration flanker task EEG dataset, the modulations of mental fatigue on IIV were explored in terms of response time (RT) and trial-to-trial latency variations of event-related potentials (ERPs). Specifically, latency variations were quantified using residue iteration decomposition (RIDE) to reconstruct latency-corrected ERPs. We compared reconstructed ERPs with raw ERPs by means of temporal principal component analysis (PCA). Furthermore, a single-trial classification pipeline was developed to detect the changes of mental fatigue levels.

RESULTS

We found an increased IIV in the RT metric in the fatigue state compared to the alert state. The same sequence of ERPs (N1, P2, N2, P3a, P3b, and slow wave, or SW) was separated from both raw and reconstructed ERPs using PCA, whereas differences between raw and reconstructed ERPs in explained variances for separated ERPs were found owing to IIV. Particularly, a stronger N2 was detected in the fatigue than alert state after RIDE. The single-trial fatigue detection pipeline yielded an acceptable accuracy of 73.3%.

COMPARISON WITH EXISTING METHODS

The IIV has been linked to aging and brain disorders, and as an extension, our finding demonstrates IIV as an efficient indicator of mental fatigue.

CONCLUSIONS

This study reveals significant modulations of mental fatigue on IIV at the behavioral and neural levels and establishes a robust mental fatigue detection pipeline.

Relationship between reaction time variability on go/no go tasks and neuropsychological functioning in younger and older adults

INTRODUCTION

Early detection of cognitive impairment in older adults is important for the prevention of dementia. Intra-individual variability in reaction time (IIV-RT) during go/no-go tasks can be used for the early detection of cognitive impairment in older adults living in the community. This study aimed to determine the relationship between IIV-RT and cognitive function during go/no-go tasks and the cutoff values for determining the risk of cognitive impairment in community-dwelling older adults.

METHODS

This study included 31 older adults without cognitive impairment, 15 community-dwelling older adults with cognitive impairment, and 34 healthy young adults. All participants performed a go/no-go task to assess the IIV-RT. Additionally, older adults underwent neuropsychological testing. Based on the results of the Japanese version of the Montreal Test of Cognitive Abilities (MoCA-J), older adults were divided into those with normal cognition and those with cognitive impairment.

RESULTS

There were significant differences in the IIV-RT among groups, including a higher IIV in the cognitively impaired group than in young adults and cognitively normal older adults. Moreover, the IIV-RT was correlated with the MoCA-J (r =  -0.531, p < 0.001), Trail Making Test Part A (r = 0.571, p < 0.001), and Verbal Fluency Test scores (r =  -0.442, p = 0.002). Receiver operating curve analysis showed that the area under the curve for IIV-RT was 0.935, and the cutoff value at which the IIV-RT identified cognitive impairment was 25.37%.

CONCLUSIONS

These findings indicate that the IIV-RT during go/no-go tasks is a useful early indicator of cognitive impairment in community-dwelling older adults.

Modulating prospective memory and attentional control with high-definition transcranial current stimulation: Study protocol of a randomized, double-blind, and sham-controlled trial in healthy older adults

The ability to remember future intentions (i.e., prospective memory) is influenced by attentional control. At the neuronal level, frontal and parietal brain regions have been related to attentional control and prospective memory. It is debated, however, whether more or less activity in these regions is beneficial for older adults' performance. We will test that by systematically enhancing or inhibiting activity in these regions with anodal or cathodal high-definition transcranial direct current stimulation in older adults. We will include n = 105 healthy older volunteers (60-75 years of age) in a randomized, double-blind, sham-controlled, and parallel-group design. The participants will receive either cathodal, anodal, or sham high-definition transcranial direct current stimulation of the left or right inferior frontal gyrus, or the right superior parietal gyrus (1mA for 20 min). During and after stimulation, the participants will complete tasks of attentional control and prospective memory. The results of this study will clarify how frontal and parietal brain regions contribute to attentional control and prospective memory in older healthy adults. In addition, we will elucidate the relationship between attentional control and prospective memory in that age group. The study has been registered with ClinicalTrials.gov on the 12th of May 2021 (trial identifier: NCT04882527).

Lower prospective memory is associated with higher neurocognitive dispersion in two samples of people with HIV: A conceptual replication study

OBJECTIVES

People living with HIV (PLWH) often experience deficits in the strategic/executive aspects of prospective memory (PM) that can interfere with instrumental activities of daily living. This study used a conceptual replication design to determine whether cognitive intraindividual variability, as measured by dispersion (IIV-dispersion), contributes to PM performance and symptoms among PLWH.

METHODS

Study 1 included 367 PLWH who completed a comprehensive clinical neuropsychological test battery, the Memory for Intentions Test (MIsT), and the Prospective and Retrospective Memory Questionnaire (PRMQ). Study 2 included 79 older PLWH who completed the Cogstate cognitive battery, the Cambridge Prospective Memory Test (CAMPROMPT), an experimental measure of time-based PM, and the PRMQ. In both studies, a mean-adjusted coefficient of variation was derived to measure IIV-dispersion using normative T-scores from the cognitive battery.

RESULTS

Higher IIV-dispersion was significantly associated with lower time-based PM performance at small-to-medium effect sizes in both studies (mean r s  = -0.30). The relationship between IIV-dispersion and event-based PM performance was comparably small in magnitude in both studies (r s  = -0.19, -0.20), but it was only statistically significant in Study 1. IIV-dispersion showed very small, nonsignificant relationships with self-reported PM symptoms in both samples (r s < 0.10).

CONCLUSIONS

Extending prior work in healthy adults, these findings suggest that variability in performance across a cognitive battery contributes to laboratory-based PM accuracy, but not perceived PM symptoms, among PLWH. Future studies might examine whether daily fluctuations in cognition or other aspects of IIV (e.g., inconsistency) play a role in PM failures in everyday life.

Inhibitory dysfunction may cause prospective memory impairment in temporal lobe epilepsy (TLE) patients: an event-related potential study

Introduction

Prospective memory (PM) is the ability to remember future intentions, and PM function is closely related to independence in daily life, particularly in patients with temporal lobe epilepsy (TLE). As PM involves various cognitive components of attention, working memory, inhibition and other executive functions, this study investigated how TLE may affect PM components and the underlying neural mechanisms.

Methods

Sixty-four subjects were recruited, including 20 refractory TLE patients, 18 well-controlled TLE patients and 26 age-matched healthy controls. A set of neuropsychological tests was administered to assess specific brain functions. An event-related potential (ERP) task was used to further explore how PM and its components would be differentially affected in the two TLE types.

Results

Our findings revealed that: (1) refractory TLE patients scored lower than the healthy controls in the digit span, Verbal Fluency Test and Symbol Digit Modalities Test; (2) refractory TLE patients exhibited impaired PM performance and reduced prospective positivity amplitudes over the frontal, central and parietal regions in ERP experiments when compared to the healthy controls; and (3) decreased P3 amplitudes in the nogo trials were observed over the frontal-central sites in refractory but not in well-controlled TLE patients.

Discussion

To our knowledge, this is the first ERP study on PM that has specifically identified PM impairment in refractory but not in well-controlled TLE patients. Our finding of double dissociation in PM components suggests that inhibition dysfunction may be the main reason for PM deficit in refractory TLE patients. The present results have clinical implications for neuropsychological rehabilitation in TLE patients.

Aging and task design shape the relationship between response time variability and emotional response inhibition

Intra-individual variability (IIV) refers to within-person variability in behavioural task responses. Several factors can influence IIV, including aging and cognitive demands. The present study investigated effects of aging on IIV of response times during executive functioning tasks. Known age-related differences in cognitive control and emotion processing motivated evaluating how varying the design of emotional response inhibition tasks would influence IIV in older and younger adults. We also tested whether IIV predicted inhibitory control across task designs and age groups. Older and younger adults (N = 237) completed one of three versions of a stop-signal task, which all displayed happy, fearful, or neutral faces in Stop trials. An independent group of older and younger adults (N = 80) completed a go/no-go task also employing happy, fearful and neutral faces. Results showed older adults had more consistent responses (lower IIV) than younger adults in the stop-signal task, but not the go/no-go task. Lower IIV predicted more efficient emotional response inhibition for fear faces in the stop-signal task, but only when attention to emotion was task-relevant. Collectively, this study clarifies effects of aging and task design on IIV and illustrates how task design impacts the relationship between IIV and emotional response inhibition in younger and older adults.

Inferring Cognitive Abilities from Response Times to Web-Administered Survey Items in a Population-Representative Sample

Monitoring of cognitive abilities in large-scale survey research is receiving increasing attention. Conventional cognitive testing, however, is often impractical on a population level highlighting the need for alternative means of cognitive assessment. We evaluated whether response times (RTs) to online survey items could be useful to infer cognitive abilities. We analyzed >5 million survey item RTs from >6000 individuals administered over 6.5 years in an internet panel together with cognitive tests (numerical reasoning, verbal reasoning, task switching/inhibitory control). We derived measures of mean RT and intraindividual RT variability from a multilevel location-scale model as well as an expanded version that separated intraindividual RT variability into systematic RT adjustments (variation of RTs with item time intensities) and residual intraindividual RT variability (residual error in RTs). RT measures from the location-scale model showed weak associations with cognitive test scores. However, RT measures from the expanded model explained 22−26% of the variance in cognitive scores and had prospective associations with cognitive assessments over lag-periods of at least 6.5 years (mean RTs), 4.5 years (systematic RT adjustments) and 1 year (residual RT variability). Our findings suggest that RTs in online surveys may be useful for gaining information about cognitive abilities in large-scale survey research.

Cognitive risk factors and the experience of acute anxiety following social stressors: An ecological momentary assessment study

To better understand how social anxiety develops, it is crucial to identify mechanisms that influence anxiety following social stressors. Anxiety sensitivity social concerns (ASSC; fear of publicly observable anxiety symptoms) and fear of negative evaluation (FNE; distress arising from concerns about negative judgment) are constructs that amplify anxiety following social stressors. However, it is unclear how ASSC and FNE influence acute anxiety following stressors in naturalistic settings. In the current study, the impact of ASSC and FNE on anxious arousal and anxious apprehension following stressors was examined in community adults (N = 83; M age = 29.66 years, SD = 12.49, 59.0% female) who completed questionnaires five times per day for two-weeks. Dynamic structural equation modeling was used to examine predictors of overall levels of anxiety as well as anxiety following social and nonsocial stressors. ASSC interacted with the presence of social stressors, such that ASSC positively predicted anxious arousal following social stressors. FNE interacted with the presence of nonsocial stressors to predict both forms of anxiety, such that FNE positively predicted anxiety following nonsocial stressors. These findings suggest ASSC may specifically amplify anxious arousal following social stressors, whereas FNE may broadly amplify anxiety following nonsocial stressors.

Longitudinal Study on Sustained Attention to Response Task (SART): Clustering Approach for Mobility and Cognitive Decline

The Sustained Attention to Response Task (SART) is a computer-based go/no-go task to measure neurocognitive function in older adults. However, simplified average features of this complex dataset lead to loss of primary information and fail to express associations between test performance and clinically meaningful outcomes. Here, we combine a novel method to visualise individual trial (raw) information obtained from the SART test in a large population-based study of ageing in Ireland and an automatic clustering technique. We employed a thresholding method, based on the individual trial number of mistakes, to identify poorer SART performances and a fuzzy clusters algorithm to partition the dataset into 3 subgroups, based on the evolution of SART performance after 4 years. Raw SART data were available for 3468 participants aged 50 years and over at baseline. The previously reported SART visualisation-derived feature ‘bad performance’, indicating the number of SART trials with at least 4 mistakes, and its evolution over time, combined with the fuzzy c-mean (FCM) algorithm, individuated 3 clusters corresponding to 3 degrees of physiological dysregulation. The biggest cluster (94% of the cohort) was constituted by healthy participants, a smaller cluster (5% of the cohort) by participants who showed improvement in cognitive and psychological status, and the smallest cluster (1% of the cohort) by participants whose mobility and cognitive functions dramatically declined after 4 years. We were able to identify in a cohort of relatively high-functioning community-dwelling adults a very small group of participants who showed clinically significant decline. The selected smallest subset manifested not only mobility deterioration, but also cognitive decline, the latter being usually hard to detect in population-based studies. The employed techniques could identify at-risk participants with more specificity than current methods, and help clinicians better identify and manage the small proportion of community-dwelling older adults who are at significant risk of functional decline and loss of independence.

Reaction time intra-individual variability reveals inhibitory deficits in single- and multiple-domain amnestic mild cognitive impairment

OBJECTIVES

Amnestic mild cognitive impairment (aMCI), a prodromal stage of Alzheimer's disease and other dementias, is characterized by episodic memory impairment. Recent evidence has shown inhibitory control deficits in aMCI, but the extent of these deficits across inhibitory domains (i.e., response inhibition and interference control) and aMCI subtypes (i.e., single- versus multiple-domain) remains unclear. Few studies have included response time intra-individual variability (RT IIV) in these efforts. The aim of this study was to compare response inhibition and interference control between aMCI subtypes using measures of accuracy, mean RT, and RT IIV.

METHOD

We report data from 34 individuals with single-domain aMCI (sdaMCI, 66-86 years), 20 individuals with multiple-domain aMCI (mdaMCI, 68-88 years), and 52 healthy controls (64-88 years) who completed tasks of response inhibition (Go-NoGo) and interference control (Flanker). Group differences in accuracy, mean RT, and RT IIV were examined for both tasks.

RESULTS

Individuals with mdaMCI had higher RT IIV than the other groups on both tasks. In RT IIV, we observed an interference control deficit in mdaMCI and sdaMCI relative to healthy controls, a finding not observed through accuracy or mean RT.

DISCUSSION

RT IIV may detect subtle differences in inhibition deficits between aMCI subtypes that may not be evident with conventional behavioral measures. Findings support the supplementary use of RT IIV when assessing early executive function deficits.

The Impact of a Sustained Cognitive Engagement Intervention on Cognitive Variability: The Synapse Project

Background

Interest in maintaining one's cognitive ability and quality of life through older adulthood has greatly increased in recent years. However, research examining the effectiveness of cognitive engagement interventions on older adults is mixed and the mechanisms behind improving cognition in older age are unknown. It is possible that traditional measures of cognitive outcomes, such as average reaction time, may overlook potential benefits due to a lack of sensitivity in these measures. One alternative metric is intraindividual variability (IIV) in response speed (short-term variations in performance on reaction time tasks), which reflects fluctuations in attention and is a sensitive behavioral measure of neurological integrity that is predictive of future cognitive decline and impairment.

Objective

The current study aimed to investigate whether IIV was improved in older adults through productive cognitive engagement (i.e., acquisition of new skills) in comparison to receptive engagement (activities that rely upon existing knowledge).

Methods

Participants were 173 typically aging adults aged 60-90 years who were recruited to the Synapse Project and randomly allocated to a productive engagement activity (learning to quilt and/or conduct digital photography) or receptive engagement activity (socializing, or placebo cognitive tasks such as completing crosswords). Participants completed three flanker tasks at baseline and after completing the 14-week intervention program. IIV was calculated as the trial-to-trial variability in responding to congruent and incongruent trials in each task.

Results

Neither traditional intent-to-treat nor complier average causal effect modeling analyses showed any significant improvements in IIV for either intervention group. Further, Bayesian analyses showed that there was moderate evidence in favor of the null hypothesis.

Conclusion

An intensive cognitive activity intervention did not result in a reduction in IIV. We suggest that intervention programs may need to specifically engage cognitive domains associated with IIV (i.e., attention, executive control) for improvements to be observed. Additionally, other design factors such as using a longer duration and/or applying the intervention to atypically aging groups, such as those with mild cognitive impairment, may increase the likelihood of significantly reducing IIV via an intervention.