Longitudinal intra-individual variability in neuropsychological performance relates to white matter changes in HIV

Cognitive Intra-individual Variability in the Laboratory Is Associated With Greater Executive Dysfunction in the Daily Lives of Older Adults With HIV

BACKGROUND

Executive dysfunction, which is common among persons with HIV (PWH), can have an adverse impact on health behaviors and quality of life. Intra-individual variability (IIV) is a measure of within-person variability across cognitive tests that is higher in PWH and is thought to reflect cognitive dyscontrol.

OBJECTIVE

To assess whether cognitive IIV in the laboratory is associated with self-reported executive dysfunction in daily life among older PWH.

METHOD

Participants included 71 PWH aged ≥50 years who completed six subtests from the Cogstate battery and two subscales from the Frontal Systems Behavior Scale (FrSBe; self-report version). Cognitive IIV was calculated from the Cogstate as the coefficient of variation derived from age-adjusted normative T scores.

RESULTS

Cognitive IIV as measured by the Cogstate showed a significant, positive, medium-sized association with current FrSBe ratings of executive dysfunction but not disinhibition.

CONCLUSION

Higher cognitive IIV in the laboratory as measured by the Cogstate may be related to the expression of HIV-associated symptoms of executive dysfunction in daily life for older PWH.

Ecological validity of cognitive fluctuations in dementia with Lewy bodies

OBJECTIVES

Cognitive fluctuations are a core clinical feature of dementia with Lewy bodies (DLB), but their contribution to the everyday functioning difficulties evident DLB are not well understood. The current study evaluated whether intraindividual variability across a battery of neurocognitive tests (intraindividual variability-dispersion) and daily cognitive fluctuations as measured by informant report are associated with worse daily functioning in DLB.

METHODS

The study sample included 97 participants with consensus-defined DLB from the National Alzheimer's Coordinating Center (NACC). Intraindividual variability-dispersion was measured using the coefficient of variation, which divides the standard deviation of an individual's performance scores across 12 normed neurocognitive indices from the NACC neuropsychological battery by that individual's performance mean. Informants reported on daily cognitive fluctuations using the Mayo Fluctuations Scale (MFS) and on daily functioning using the functional activities questionnaire (FAQ).

RESULTS

Logistic regression identified a large univariate association of intraindividual variability-dispersion and presence of daily cognitive fluctuations on the MFS (Odds Ratio = 73.27, 95% Confidence Interval = 1.38, 3,895.05). Multiple linear regression demonstrated that higher intraindividual variability-dispersion and presence of daily cognitive fluctuations as assessed by the MFS were significantly and independently related to worse daily functioning (FAQ scores).

CONCLUSIONS

Among those with DLB, informant-rated daily cognitive fluctuations and cognitive fluctuations measured in the clinic (as indexed by intraindividual variability-dispersion across a battery of tests) were independently associated with poorer everyday functioning. These data demonstrate ecological validity in measures of cognitive fluctuations in DLB.

Cognitive intra-individual variability in breast cancer survivors: A systematic review

Subjective and objective cognitive impairments in Breast Cancer Survivors (BCS) often do not correlate. One important contribution to the reported disparities may be the reliance on mean-based cognitive performance. Cognitive intra-individual variability (IIV) may provide important insights into these reported disparities. Cognitive IIV refers to the fluctuation in performance for an individual on either one cognitive task across a trial or dispersed across tasks within a neuropsychological test battery. The purpose of this systematic review was to search for and examine the literature on cognitive IIV in BCS. The PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) approach was used to search for all articles related to cognitive IIV in BCS. MEDLINE (via PubMed), Embase, and Scopus databases were searched using detailed search terms and strategies. Initially, 164 articles were retrieved but only 4 articles met the criteria for this systematic review. BCS differed from healthy controls in similar ways across the four studies, generally demonstrating similar performance but showing increased cognitive IIV for the more difficult tasks. Differences were enhanced later during chemotherapy. The four studies provide support for cognitive IIV as a useful measure to detect the subtle objective cognitive change often reported by BCS but frequently not detected by standard normed-based cognitive testing. Unexpectedly, measures of cognitive IIV were not consistently associated with self-reported measures of cognition.

Recent Advances in Neuropsychological Test Interpretation for Clinical Practice

Much attention in the field of clinical neuropsychology has focused on adapting to the modern healthcare environment by advancing telehealth and promoting technological innovation in assessment. Perhaps as important (but less discussed) are advances in the development and interpretation of normative neuropsychological test data. These techniques can yield improvement in diagnostic decision-making and treatment planning with little additional cost. Brooks and colleagues (Can Psychol 50: 196-209, 2009) eloquently summarized best practices in normative data creation and interpretation, providing a practical overview of norm development, measurement error, the base rates of low scores, and methods for assessing change. Since the publication of this seminal work, there have been several important advances in research on development and interpretation of normative neuropsychological test data, which may be less familiar to the practicing clinician. Specifically, we provide a review of the literature on regression-based normed scores, item response theory, multivariate base rates, summary/factor scores, cognitive intraindividual variability, and measuring change over time. For each topic, we include (1) an overview of the method, (2) a rapid review of the recent literature, (3) a relevant case example, and (4) a discussion of limitations and controversies. Our goal was to provide a primer for use of normative neuropsychological test data in neuropsychological practice.

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.

Moving intra-individual variability (IIV) towards clinical utility: IIV measured using a commercial testing platform

OBJECTIVES

Intra-individual variability (IIV), measured across repeated response times (RT) during continuous psychomotor tasks, is an early marker of cognitive change in the context of neurodegeneration. To advance IIV towards broader application in clinical research, we evaluated IIV from a commercial cognitive testing platform and compared it to the calculation approaches used in experimental cognitive studies.

METHODS

Cognitive assessment was administered in participants with multiple sclerosis (MS) during the baseline of an unrelated study. Cogstate was used for computer-based measures providing three timed-trial tasks measuring simple (Detection; DET) and choice (Identification; IDN) RT and working memory (One-Back; ONB). IIV for each task was automatically output by the program (calculated as a log₁₀-transformed standard deviation or "LSD"). We calculated IIV from the raw RTs using coefficient of variation (CoV), regression-based, and ex-Gaussian methods. The IIV from each calculation was then compared by rank across participants.

RESULTS

A total of n = 120 participants with MS aged 20-72 (Mean ± SD, 48.99 ± 12.09) completed the baseline cognitive measures. For each task, the interclass correlation coefficient was generated. Each ICC showed that LSD, CoV, ex-Gaussian, and regression methods clustered strongly (Average ICC for DET: 0.95 with 95% CI [0.93, 0.96]; Average ICC for IDN: 0.92 with 95% CI [0.88 to 0.93]; Average ICC for ONB: 0.93 with 95% CI [0.90 to 0.94]). Correlational analyses indicated the strongest correlation between LSD and CoV for all tasks (rs ≥ 0.94).

CONCLUSION

The LSD was consistent with research-based methods for IIV calculations. These findings support the use of LSD for the future measurement of IIV for clinical studies.

Neuroimaging and immunological features of neurocognitive function related to substance use in people with HIV

This study sought to identify neuroimaging and immunological factors associated with substance use and that contribute to neurocognitive impairment (NCI) in people with HIV (PWH). We performed cross-sectional immunological phenotyping, neuroimaging, and neurocognitive testing on virally suppressed PWH in four substance groups: cocaine only users (COC), marijuana only users (MJ), dual users (Dual), and Non-users. Participants completed substance use assessments, multimodal MRI brain scan, neuropsychological testing, and blood and CSF sampling. We employed a two-stage analysis of 305 possible biomarkers of cognitive function associated with substance use. Feature reduction (Kruskal Wallis p-value < 0.05) identified 53 biomarkers associated with substance use (22 MRI and 31 immunological) for model inclusion along with clinical and demographic variables. We employed eXtreme Gradient Boosting (XGBoost) with these markers to predict cognitive function (global T-score). SHapley Additive exPlanations (SHAP) values were calculated to rank features for impact on model output and NCI. Participants were 110 PWH with sustained HIV viral suppression (33 MJ, 12 COC, 22 Dual, and 43 Non-users). The ten highest ranking biomarkers for predicting global T-score were 4 neuroimaging biomarkers including functional connectivity, gray matter volume, and white matter integrity; 5 soluble biomarkers (plasma glycine, alanine, lyso-phosphatidylcholine (lysoPC) aC17.0, hydroxy-sphingomyelin (SM.OH) C14.1, and phosphatidylcholinediacyl (PC aa) C28.1); and 1 clinical variable (nadir CD4 count). The results of our machine learning model suggest that substance use may indirectly contribute to NCI in PWH through both metabolomic and neuropathological mechanisms.

Cognitive Intra-individual Variability in HIV: an Integrative Review

Nearly 30-50% of people living with HIV experience HIV-Associated Neurocognitive Disorder (HAND). HAND indicates performance at least one standard deviation below the normative mean on any two cognitive domains. This method for diagnosing or classifying cognitive impairment has utility, however, cognitive intraindividual variability provides a different way to understand cognitive impairment. Cognitive intraindividual variability refers to the scatter in cognitive performance within repeated measures of the same cognitive test (i.e., inconsistency) or across different cognitive tests (i.e., dispersion). Cognitive intraindividual variability is associated with cognitive impairment and cognitive decline in various clinical populations. This integrative review of 13 articles examined two types of cognitive intraindividual variability in people living with HIV, inconsistency and dispersion. Cognitive intraindividual variability appears to be a promising approach to detect subtle cognitive impairments that are not captured by traditional mean-based neuropsychological testing. Greater intraindividual variability in people living with HIV has been associated with: 1) poorer cognitive performance and cognitive decline, 2) cortical atrophy, both gray and white matter volume, 3) poorer everyday functioning (i.e., driving simulation performance), specifically medication adherence, and 4) even mortality. This inspires future directions for research. First, greater cognitive intraindividual variability may reflect a greater task demand on executive control to harness and regulate cognitive control over time. By improving executive functioning through cognitive training, it may reduce cognitive intraindividual variability which could slow down cognitive decline. Second, cognitive intraindividual variability may be reconsidered in prior cognitive intervention studies in which only mean-based cognitive outcomes were used. It is possible that such cognitive interventions may actually improve cognitive intraindividual variability, which could have clinical relevance.

Intraindividual variability in neuropsychological performance predicts longitudinal cortical volume loss in early Parkinson's disease

OBJECTIVE

Cognitive impairment is common among individuals with Parkinson's disease (PD). Intraindividual variability (IIV) is a measure of variability across multiple tasks of cognitive functioning. Due to the limited amount of research, particularly among individuals with PD, IIV has been an underutilized metric of cognitive functioning both in research and clinical practice. Previous research demonstrated that individuals with PD have greater variability in cognitive performance relative to controls, and that IIV is predictive of future cognitive impairments. The aim of this study is to investigate the association between baseline IIV and change in cortical and subcortical volumes among individuals with PD.

METHOD

The present study used data from 80 newly diagnosed PD patients who were part of a longitudinal cohort study (Parkinson progression marker initiative [PPMI]). Participants completed neuropsychological measures and underwent T1 structural magnetic resonance imaging (MRI) at baseline and the first annual follow-up. Neuropsychological tests assessed attention, processing speed, visuospatial functioning, verbal fluency learning, and memory. T1 scans were processed using standard Freesurfer protocols for extraction of regional volumes.

RESULTS

Greater IIV at baseline was predictive of change in cortical volume in posterior temporal/parietal regions over the 1-year period. Baseline IIV predicted cortical volume changes above and beyond the main effect of motor severity and the baseline statistical mean/global cognition score.

CONCLUSION

Our results provide initial evidence that IIV is a marker of longitudinal cortical volume loss. Evidence is building that IIV is a sensitive marker of cognitive impairment and the underlying neurodegeneration among individuals with PD. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Longitudinal Intraindividual Cognitive Variability Is Associated With Reduction in Regional Cerebral Blood Flow Among Alzheimer's Disease Biomarker-Positive Older Adults

Intraindividual variability (IIV) across neuropsychological measures within a single testing session is a promising marker predictive of cognitive decline and development of Alzheimer's disease (AD). We have previously shown that greater IIV is cross-sectionally associated with reduced cerebral blood flow (CBF), but not with cortical thickness or brain volume, in older adults without dementia who were amyloid beta (Aβ) positive. However, there is little known about the association between change in IIV and CBF over time. Therefore, we examined 12-month longitudinal change in IIV and interactions of IIV and AD biomarker status on changes in regional CBF. Fifty-three non-demented Alzheimer's Disease Neuroimaging Initiative (ADNI) participants underwent lumbar puncture to obtain cerebrospinal fluid (CSF) at baseline and neuropsychological testing and magnetic resonance imaging (MRI) exams at baseline and 12-month follow-up evaluation. IIV was calculated as the intraindividual standard deviation across 6 demographically-corrected neuropsychological measures. Pulsed arterial spin labeling (ASL) MRI was acquired to quantify CBF and FreeSurfer-derived a priori CBF regions of interest (ROIs) were examined. AD biomarker positivity was determined using a published CSF p-tau/Aβ ratio cut-score. Change scores were calculated for IIV, CBF, and mean neuropsychological performance from baseline to 12 months. Hierarchical linear regression models showed that after adjusting for age and gender, there was a significant interaction between IIV change and biomarker-positivity (p-tau/Aβ+) for change in entorhinal and hippocampal CBF but not for the other ROIs. Specifically, increases in IIV were associated with reductions in entorhinal and hippocampal CBF among individuals who were biomarker-positive (n = 21). In contrast, there were no significant associations between change in IIV and CBF among those who were biomarker-negative (n = 32). Findings remained similar when analyses were performed adjusting for change in mean level of neuropsychological performance. Changes in IIV may be sensitive to changes in regional hypoperfusion in AD-vulnerable regions among AD biomarker-positive individuals, above and beyond demographics and mean neuropsychological performance. These findings provide further evidence supporting IIV as a potential marker of cerebrovascular brain changes in individuals at risk for dementia.

Machine Learning Quantifies Accelerated White-Matter Aging in Persons With HIV

BACKGROUND

Persons with HIV (PWH) undergo white matter changes, which can be quantified using the brain-age gap (BAG), the difference between chronological age and neuroimaging-based brain-predicted age. Accumulation of microstructural damage may be accelerated in PWH, especially with detectable viral load (VL).

METHODS

In total, 290 PWH (85% with undetectable VL) and 165 HIV-negative controls participated in neuroimaging and cognitive testing. BAG was measured using a Gaussian process regression model trained to predict age from diffusion magnetic resonance imaging in publicly available normative controls. To test for accelerated aging, BAG was modeled as an age × VL interaction. The relationship between BAG and global neuropsychological performance was examined. Other potential predictors of pathological aging were investigated in an exploratory analysis.

RESULTS

Age and detectable VL had a significant interactive effect: PWH with detectable VL accumulated +1.5 years BAG/decade versus HIV-negative controls (P = .018). PWH with undetectable VL accumulated +0.86 years BAG/decade, although this did not reach statistical significance (P = .052). BAG was associated with poorer global cognition only in PWH with detectable VL (P < .001). Exploratory analysis identified Framingham cardiovascular risk as an additional predictor of pathological aging (P = .027).

CONCLUSIONS

Aging with detectable HIV and cardiovascular disease may lead to white matter pathology and contribute to cognitive impairment.

Human immunodeficiency virus-related decreases in corpus callosal integrity and corresponding increases in functional connectivity

People living with human immunodeficiency virus (PLWH) often have neurocognitive impairment. However, findings on HIV-related differences in brain network function underlying these impairments are inconsistent. One principle frequently absent from these reports is that brain function is largely emergent from brain structure. PLWH commonly have degraded white matter; we hypothesized that functional communities connected by degraded white matter tracts would show abnormal functional connectivity. We measured white matter integrity in 69 PLWH and 67 controls using fractional anisotropy (FA) in 24 intracerebral white matter tracts. Then, among tracts with degraded FA, we identified gray matter regions connected to these tracts and measured their functional connectivity during rest. Finally, we identified cognitive impairment related to these structural and functional connectivity systems. We found HIV-related decreased FA in the corpus callosum body (CCb), which coordinates activity between the left and right hemispheres, and corresponding increases in functional connectivity. Finally, we found that individuals with impaired cognitive functioning have lower CCb FA and higher CCb functional connectivity. This result clarifies the functional relevance of the corpus callosum in HIV and provides a framework in which abnormal brain function can be understood in the context of abnormal brain structure, which may both contribute to cognitive impairment.

Elevated Intraindividual Variability in Executive Functions and Associations with White Matter Microstructure in Veterans with Mild Traumatic Brain Injury

OBJECTIVE

We examined whether intraindividual variability (IIV) across tests of executive functions (EF-IIV) is elevated in Veterans with a history of mild traumatic brain injury (mTBI) relative to military controls (MCs) without a history of mTBI. We also explored relationships among EF-IIV, white matter microstructure, and posttraumatic stress disorder (PTSD) symptoms.

METHOD

A total of 77 Veterans (mTBI = 43, MCs = 34) completed neuropsychological testing, diffusion tensor imaging (DTI), and PTSD symptom ratings. EF-IIV was calculated as the standard deviation across six tests of EF, along with an EF-Mean composite. DSI Studio connectometry analysis identified white matter tracts significantly associated with EF-IIV according to generalized fractional anisotropy (GFA).

RESULTS

After adjusting for EF-Mean and PTSD symptoms, the mTBI group showed significantly higher EF-IIV than MCs. Groups did not differ on EF-Mean after adjusting for PTSD symptoms. Across groups, PTSD symptoms significantly negatively correlated with EF-Mean, but not with EF-IIV. EF-IIV significantly negatively correlated with GFA in multiple white matter pathways connecting frontal and more posterior regions.

CONCLUSIONS

Veterans with mTBI demonstrated significantly greater IIV across EF tests compared to MCs, even after adjusting for mean group differences on those measures as well as PTSD severity. Findings suggest that, in contrast to analyses that explore effects of mean performance across tests, discrepancy analyses may capture unique variance in neuropsychological performance and more sensitively capture cognitive disruption in Veterans with mTBI histories. Importantly, findings show that EF-IIV is negatively associated with the microstructure of white matter pathways interconnecting cortical regions that mediate executive function and attentional processes.

Loss of Consciousness is Associated with Elevated Cognitive Intra-Individual Variability Following Sports-Related Concussion

OBJECTIVE

The purpose of this study was to evaluate whether loss of consciousness (LOC), retrograde amnesia (RA), and anterograde amnesia (AA) independently influence a particular aspect of post-concussion cognitive functioning-across-test intra-individual variability (IIV), or cognitive dispersion.

METHOD

Concussed athletes (N = 111) were evaluated, on average, 6.04 days post-injury (SD = 5.90; Mdn = 4 days; Range = 1-26 days) via clinical interview and neuropsychological assessment. Primary outcomes of interest included two measures of IIV-an intra-individual standard deviation (ISD) score and a maximum discrepancy (MD) score-computed from 18 norm-referenced variables.

RESULTS

Analyses of covariance (ANCOVAs) adjusting for time since injury and sex revealed a significant effect of LOC on the ISD (p = .018, ηp2 = .051) and MD (p = .034, ηp2 = .041) scores, such that athletes with LOC displayed significantly greater IIV than athletes without LOC. In contrast, measures of IIV did not significantly differ between athletes who did and did not experience RA or AA (all p > .05).

CONCLUSIONS

LOC, but not RA or AA, was associated with greater variability, or inconsistencies, in cognitive performance acutely following concussion. Though future studies are needed to verify the clinical significance of these findings, our results suggest that LOC may contribute to post-concussion cognitive dysfunction and may be a risk factor for less efficient cognitive functioning.

Vagal Flexibility Mediates the Association Between Resting Vagal Activity and Cognitive Performance Stability Across Varying Socioemotional Demands

Vagal flexibility describes the ability to modulate cardiac vagal responses to fit a dynamic range of challenges. Extant theory on vagal function implies that vagal flexibility is a mediating mechanism through which resting vagal activity, a putative individual difference related to self-regulation, affects adaptive behavior and cognition. Nevertheless, little research has directly tested this hypothesis, thereby leaving fundamental mechanisms of vagal function and adaptability unclear. To this end, 47 healthy subjects completed a 5 min baseline followed by Stroop tasks combined with concurrent auditory distractors. There were four different Stroop task conditions that varied the social and emotional content of the auditory distractors. Electrocardiogram was continuously recorded to assess vagal responses to each condition as heart rate variability [root mean square of successive differences (RMSSDs)] reactivity. Vagal flexibility significantly mediated the association between resting vagal activity and stability of inhibition performance (Stroop interference) scores. In particular, higher resting RMSSD was related to higher standard deviation of RMSSD reactivity scores, reflecting greater differences in RMSSD reactivity between distractor conditions (i.e., greater vagal flexibility). Greater vagal flexibility was in turn related to more stability in Stroop interference across the same conditions. The mean of RMSSD reactivity scores across conditions was not significantly related to resting RMSSD or stability in Stroop performance, and mean RMSSD reactivity did not mediate relations between resting RMSSD and stability in Stroop performance. Overall, findings suggest that vagal flexibility may promote the effects of resting vagal activity on stabilizing cognitive inhibition in the face of environmental perturbations.

The association of white matter free water with cognition in older adults

BACKGROUND

Extracellular free water within cerebral white matter tissue has been shown to increase with age and pathology, yet the cognitive consequences of free water in typical aging prior to the development of neurodegenerative disease remains unclear. Understanding the contribution of free water to cognitive function in older adults may provide important insight into the neural mechanisms of the cognitive aging process.

METHODS

A diffusion-weighted MRI measure of extracellular free water as well as a commonly used diffusion MRI metric (fractional anisotropy) along nine bilateral white matter pathways were examined for their relationship with cognitive function assessed by the NIH Toolbox Cognitive Battery in 47 older adults (mean age ​= ​74.4 years, SD ​= ​5.4 years, range ​= ​65-85 years). Probabilistic tractography at the 99th percentile level of probability (Tracts Constrained by Underlying Anatomy; TRACULA) was utilized to produce the pathways on which microstructural characteristics were overlaid and examined for their contribution to cognitive function independent of age, education, and gender.

RESULTS

When examining the 99th percentile probability core white matter pathway derived from TRACULA, poorer fluid cognitive ability was related to higher mean free water values across the angular and cingulum bundles of the cingulate gyrus, as well as the corticospinal tract and the superior longitudinal fasciculus. There was no relationship between cognition and mean FA or free water-adjusted FA across the 99th percentile core white matter pathway. Crystallized cognitive ability was not associated with any of the diffusion measures. When examining cognitive domains comprising the NIH Toolbox Fluid Cognition index relationships with these white matter pathways, mean free water demonstrated strong hemispheric and functional specificity for cognitive performance, whereas mean FA was not related to age or cognition across the 99th percentile pathway.

CONCLUSIONS

Extracellular free water within white matter appears to increase with normal aging, and higher values are associated with significantly lower fluid but not crystallized cognitive functions. When using TRACULA to estimate the core of a white matter pathway, a higher degree of free water appears to be highly specific to the pathways associated with memory, working memory, and speeded decision-making performance, whereas no such relationship existed with FA. These data suggest that free water may play an important role in the cognitive aging process, and may serve as a stronger and more specific indicator of early cognitive decline than traditional diffusion MRI measures, such as FA.

Neurocognitive intra-individual variability within HIV+ adults with and without current substance use

OBJECTIVE

HIV infection and current substance use (SU) are linked to cognitive and functional deficits, yet findings on their combined effects are mixed. Neurocognitive intraindividual variability, measured as dispersion of scores across a neuropsychological battery, is associated with worse cognitive outcomes and functional deficits among HIV+ adults but has not been studied in the context of HIV+ adults with current SU. We hypothesized that, among HIV+ adults, current SU would be associated with greater dispersion, that greater dispersion would be associated with worse medication adherence, and that this relationship would be worse among substance users.

METHOD

Forty HIV+ adults completed neuropsychological, psychiatric, SU, and medical evaluations and an electronic medication adherence measure. General linear models evaluated the main effect of SU status on neurocognitive dispersion, and models stratified by SU status evaluated the effect of dispersion on medication adherence, adjusting for relevant covariates.

RESULTS

The SU+ group showed greater dispersion than did the SU- group, t(38) = 2.74, p = .049, d = 0.81, but this association did not survive multiple comparisons. Stratified analyses indicated a negative relationship between dispersion and medication adherence among the SU+ group but not in the SU- group; however, this effect was reduced after accounting for depressive symptoms.

CONCLUSIONS

We found preliminary evidence that current SU is associated with greater neurocognitive dispersion among HIV+ adults. SU and neurocognitive dispersion may have a synergistic effect on medication adherence; however, this effect is largely accounted for by depressive symptoms. Future research should examine progression of dispersion in HIV and consequent neurocognitive and functional deficits in those with current SU. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Greater intraindividual variability in neuropsychological performance predicts cognitive impairment in de novo Parkinson's disease

INTRODUCTION

Parkinson's disease (PD) is a neurodegenerative disorder that commonly results in cognitive impairments and dementia. Intraindividual variability of neuropsychological performance is a sensitive marker of cognitive decline in other neurologic populations. However, studies have not examined the longitudinal utility of intraindividual variability in predicting future cognitive impairments among individuals with PD. In the current study, we hypothesized that increased intraindividual variability would predict future cognitive decline independent of traditional neuropsychological markers of cognitive impairment.

METHODS

The sample included 423 newly diagnosed PD patients and 175 healthy controls, who were followed up to 5 years (baseline, first, second, third, fourth, and fifth annual follow-up). Participants underwent tests of learning, memory, processing speed, attention, verbal fluency, and visuospatial functioning. Cognitive status (cognitive intact, mild cognitive impairment, and dementia) was classified based on previously established criteria. Multilevel models were computed to examine the longitudinal relationship between intraindividual variability, cognitive status, and general cognitive functioning.

RESULTS

Analyses revealed that increased intraindividual variability was predictive of incident cognitive decline among individuals with PD. Specifically, greater dispersion in neuropsychological performance was associated with greater risk of transitioning from cognitively intact to mild cognitive impairment or transitioning from mild cognitive impairment to dementia. Additional analyses revealed a significant Intraindividual Variability × Group (PD or control) interaction, meaning that intraindividual variability was predictive of declines in cognitive functioning among PD participants only but not healthy controls.

CONCLUSION

Intraindividual variability may be a harbinger for future cognitive decline among individuals with PD. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Reliably Measuring Cognitive Change in the Era of Chronic HIV Infection and Chronic HIV-Associated Neurocognitive Disorders

HIV infection has become a chronic disease managed across the life span. In this context, the cognitive health of HIV infection needs to have methods for monitoring over time, in order to better anticipate HIV-associated neurocognitive disorder (HAND) trajectories in relation to biomarkers, and predict prognosis and especially the risk of dementia as People Living with HIV (PLHIV) age. In this chapter, we critically review several statistical frameworks to quantify cognitive change. We then provide a critical review of naturalistic longitudinal studies and selected randomized clinical trials assessing neurocognitive change as a primary outcome in PLHIV, conducted since the advent of the combined antiretroviral therapy era (censored January 2019). Doing so, we distinguish between PLHIV who were treated early and did not experience AIDS (CDC 1993), versus treated late, after experiencing AIDS and more severe immune compromise. Highlighting strengths and limitations of these studies, we emphasize that issues of reliability pertaining to the use of neuropsychological tests need careful consideration for the robust quantification of cognitive change, including measurement error, practice effect, inter-individual variability, baseline level of functioning, demographic effects, timeframe between testing intervals, normative longitudinal data, and operationalization of clinically meaningful neurocognitive change. In addition, issues pertaining to longitudinal analyses including type, amount and pattern of missing data and/or participant attrition, regression toward the mean, and survivor bias need to be properly addressed. We conclude by proposing future research directions with emphasis on research translation to clinical participants.

Intraindividual variability in neuropsychological performance predicts cognitive decline and death in HIV

OBJECTIVE

HIV-associated neurocognitive disorder (HAND) occurs in a significant percentage of HIV-infected (HIV+) adults. Increased intraindividual variability (IIV) in cognitive function may be an early marker of emerging neurocognitive disorder, which suggests that IIV may be a sensitive measure of neurologic compromise in HIV. In the current study, we hypothesize that increased IIV may predict impending morbidity, including future cognitive decline and death.

METHOD

In 708 HIV+ participants followed longitudinally for up to 14 years, we assessed the role of dispersion in forecasting death and cognitive decline. Incident neurocognitive impairment was predicted in a mixed-effects ordinal logistic regression model using age, gender, baseline mean cognitive functioning, CD4+, time followed, years of education, and dispersion at the previous visit. Death before the next visit was predicted in a binomial mixed-effects regression model using age, gender, baseline mean cognitive functioning, CD4+, time followed, years of education, and dispersion.

RESULTS

Point-in-time dispersion and change in dispersion between visits predict future cognitive decline and death in HIV+ individuals. Individuals with greater dispersion at a visit or who had larger changes in dispersion between visits were more likely to demonstrate greater neurocognitive impairment at the subsequent visit. Greater IIV was also associated with an increased risk of death prior to the subsequent visit, even after controlling for HAND severity and global cognitive functioning.

CONCLUSIONS

We conclude that the IIV in cognitive functioning may be more predictive of future disease consequence than mean level of cognitive functioning. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

The Impact of Alcohol Use on Frontal White Matter in HIV

BACKGROUND

Alcohol use disorder (AUD) is prevalent among individuals diagnosed with human immunodeficiency virus (HIV), and both HIV and alcohol use have been shown to negatively affect the integrity of white matter pathways in the brain. Behavioral, functional, and anatomical impairments have been linked independently to HIV and alcohol use, and these impairments have bases in specific frontally mediated pathways within the brain.

METHODS

Magnetic resonance imaging data were acquired for 37 HIV+ participants without dementia or hepatitis C. Imaging data were processed through the FreeSurfer and TraCULA pipelines to obtain 4 bilateral frontal white matter tracts for each participant. Diffusion metrics of white matter integrity along the highest probability pathway for each tract were analyzed with respect to demographics, disease-specific variables, and reported substance use.

RESULTS

Significantly increased axial diffusivity (decreased axonal integrity) and a trending increase in mean diffusivity were observed along the anterior thalamic radiation (ATR) in participants with a history of AUD. A diagnosis of AUD explained over 36% of the variance in diffusivity along the ATR overall when accounting for clinical variables including nadir CD4 and age-adjusted HIV infection length.

CONCLUSIONS

This study provides evidence of HIV-related associations between alcohol use and indicators of axonal integrity loss along the ATR, a frontal pathway involved in the inhibition of addictive or unwanted behaviors. Reduced axonal integrity of this pathway was greatest in HIV+ participants with an AUD, even when considering the effect of age-adjusted disease length and severity (nadir CD4). This finding implicates a potential biological mechanism linking reduced integrity of frontal white matter to the high prevalence of AUD in an HIV+ population without dementia or hepatitis C.