Cognitive Intraindividual Variability Research Articles

Unemployment Status Is Associated With Greater Cognitive Intraindividual Variability in Veterans With a History of Remote Mild TBI.

To examine the association between employment status and neuropsychological functioning in veterans with a history of remote mild traumatic brain injury (mTBI) using 2 approaches to assess cognitive performance: (a) standard, traditional mean cognitive performance; and (b) across-test intraindividual variability (IIV). Outpatient Veterans Affairs (VA) hospital. Eligibility criteria included veterans with a history of mTBI who performed adequately on performance validity tests. Participants (N = 75; 37 employed, 38 unemployed) were evaluated, on average, about 5.5 years after their most recent mTBI. Observational cohort study; all participants completed a clinical interview and a comprehensive neuropsychological assessment. Primary outcomes of interest included mean cognitive composite test scores and IIV scores on tasks of memory, attention/processing speed, and executive functioning. Logistic regression models showed that mean cognitive performance was not predictive of employment status; however, IIV indices were ( = 7.88, P = .048) and accounted for 13% of the variance. Greater memory-IIV was significantly associated with being unemployed (β = -.16, SE = .07, P = .020, Exp(B) = 0.85; 95% CI, 0.74-0.98). These findings build upon prior work showing that IIV, or cognitive dispersion, is associated with important functional outcomes following mTBI, including employment status. Future studies are needed to verify these findings, but the present study suggests that IIV indices offer a clinically meaningful marker of cognitive functioning and should be considered when evaluating functional outcomes following head trauma.

Cerebrospinal fluid Aβ42 moderates the relationship between brain functional network dynamics and cognitive intraindividual variability

As Alzheimer’s disease (AD) pathology accumulates, resting-state functional connectivity (rs-fc) within and between brain networks decreases, and fluctuations in cognitive performance known as intraindividual variability (IIV) increase. Here, we assessed the relationship between IIV and anticorrelations in rs-fc between the default mode network (DMN)-dorsal attention network (DAN) in cognitively normal older adults and symptomatic AD participants. We also evaluated the relationship between cerebrospinal fluid (CSF) biomarkers of AD (amyloid-beta [Aβ42] and tau) and IIV-anticorrelation in rs-fc. We observed that cognitive IIV and anticorrelations between DMN × DAN were higher in individuals with AD compared with cognitively normal participants. As DMN × DAN relationship became more positive, cognitive IIV increased, indicating that stronger anticorrelations between networks support more consistent cognitive performance. Moderation analyses indicated that continuous CSF Aβ42, but not CSF total tau, moderated the relationship between cognitive IIV and DMN × DAN, collectively demonstrating that greater amyloid burden and alterations in functional network dynamics are associated with cognitive changes seen in AD. These findings are valuable, as they suggest that amyloid affects cognitive functioning during the early stages of AD.

A-012 Meta-Analysis of Neuropsychological Intra-Individual Variability in Dementia and Mild-Cognitive Impairment

Abstract Objective Neuropsychological intra-individual variability (IIV) refers to within-person cognitive fluctuation. It is often measured within-task (i.e., consistency) and across-tasks (i.e., dispersion). This investigation meta-analyzed studies comparing cognitive IIV of dementia and mild cognitive impairment (MCI) participants to normal controls. Method Eight databases within the EBSCO network as well as ProQuest Dissertations & Theses were searched for original research comparing cognitive IIV between clinical and control samples. Studies were coded using a complex multi-comparison, outcome, and subgroup schema. All data were analyzed under random-effects modeling using Comprehensive Meta-Analysis. Main index of effect size was Hege’s g. The Q and I2 statistics were used to formally assess heterogeneity. Continuous and categorical moderator variables were tested using meta-regression and subgroup analysis, respectively. Results This study was a part of a broader meta-analysis looking at IIV across all clinical samples. The initial search strategy yielded 2,962 results, which were reduced to 87 studies for final inclusion. From which, the current meta-analysis included 28 consistency studies (dementia: k = 13, 88 effect sizes; MCI: k = 15, 110 effect sizes) and 16 dispersion studies (dementia: k = 10, 36 effect sizes; MCI: k = 6, 14 effect sizes). Meta-analysis revealed a greater combined effect size for dementia samples (consistency: g = 0.92; dispersion: g = 1.11) than MCI (consistency: g = 0.33; dispersion: g = 0.56). Significant between-study heterogeneity was noted across analyses. Age and education were the only notable moderators. Conclusions All clinical subgroups demonstrated significantly elevated IIV compared to controls. The extent of IIV was proportionate to neurologic burden. Dispersion-based IIV may be a more sensitive marker of neural integrity than consistency.

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

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. 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. 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). 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.

The role of intraindividual cognitive variability in posttraumatic stress syndromes and cognitive aging: a literature search and proposed research agenda.

Cognitive impairments are directly related to severity of symptoms and are a primary cause for functional impairment. Intraindividual cognitive variability likely plays a role in both risk and resiliency from symptoms. In fact, such cognitive variability may be an earlier marker of cognitive decline and emergent psychiatric symptoms than traditional psychiatric or behavioral symptoms. Here, our objectives were to survey the literature linking intraindividual cognitive variability, trauma, and dementia and to suggest a potential research agenda. A wide body of literature suggests that exposure to major stressors is associated with poorer cognitive performance, with intraindividual cognitive variability in particular linked to the development of posttraumatic stress disorder (PTSD) in the aftermath of severe trauma. In this narrative review, we survey the empirical studies to date that evaluate the connection between intraindividual cognitive variability, PTSD, and pathological aging including dementia. The literature suggests that reaction time (RT) variability within an individual may predict future cognitive impairment, including premature cognitive aging, and is significantly associated with PTSD symptoms. Based on our findings, we argue that intraindividual RT variability may serve as a common pathological indicator for trauma-related dementia risk and should be investigated in future studies.

Using Cognitive Intraindividual Variability to Measure Intervention Effectiveness: Results from the Baltimore Experience Corps Trial.

Studies investigating the effectiveness of intervention programs on cognitive ability in older adults are inconsistent; however, these studies generally focus on traditional measures of cognition, and therefore may miss some improvements by not utilizing alternate measures. We evaluate the potential for intraindividual variability in cognitive speed (IIV), a demonstrated sensitive indicator of cognitive functioning, to be used as an index of cognitive plasticity from an intervention. The current study evaluated whether older adults in a school volunteering program showed a reduction in IIV, compared to a low-activity control group over 2 years of exposure. Nondemented older adults (n = 336) participated in the Baltimore Experience Corps Trial, an evaluation of a volunteering program conducted at elementary schools designed to increase older adults' physical, cognitive, and social engagement. Participants completed a cognitive battery that included a Stroop task at baseline and after 12 and 24 months. Traditional intent-to-treat analyses did not report significant improvements. Participants who complied at the 80th percentile or above showed a significant reduction in IIV at 24 months, with an additional trend of improved IIV with increased compliance to the treatment protocol, both at 12 months, and at 24 months. Men also showed dose-dependent improvements after 12 months. The Experience Corps program resulted in an improvement in cognitive performance as measured by IIV. Analyzing previously collected data with nontraditional measures of cognition, such as IIV, may be a potentially fruitful and cost-effective method for understanding how interventions impact cognition in aging populations.

C-13 Sex Differences in Cognitive and Neurobiological Markers of Alzheimer's Disease

Abstract Objective Previous work has demonstrated that intra-individual cognitive variability (IICV) has predictive power similar to traditional Alzheimer’s disease (AD) biomarkers, such as CSF or hippocampal volume (HV) loss. Genetic factors, such as sex, have been identified as predictors of cognitive decline. Analysis of sex differences in IICV and other biomarkers may elucidate additional dimensions of this metric. Method Baseline neurocognitive test and neuroimaging data from 335 participants with ≥2 visits enrolled in the Wisconsin Alzheimer’s Disease Research Center Clinical Core were included. Z-scores were calculated comparing individual performance to group performance by test (Rey Auditory Verbal Learning Test (Learning and Delayed Recall), Trail Making Test (A and B), and either Boston Naming Test (BNT) or Multilingual Naming Test (MINT)). MINT scores were converted to BNT scores using the NACC Crosswalk Study. The standard deviation of z-scores across tests was calculated to determine IICV. Characteristics by sex were compared using Mann-Whitney and Fisher’s Exact tests. Spearman’s Rho was calculated to compare IICV and HV (relative to intercranial volume). Results At baseline (Table 1): (1) Males had more education than females; (2) females had both higher relative HV and IICV; and (3) in females, relative HV demonstrated a weak positive correlation with baseline IICV (Figure 1). Conclusions IICV has previously demonstrated potential as a cost-effective non-invasive marker of preclinical AD. In females, larger relative HV and its correlation with IICV may be due to differences in metabolic brain age or concurrent progression of HV and IICV through the AD process. Analyses of other biopsychosocial factors are needed.

Cognitive dispersion is a sensitive marker for early neurodegenerative changes and functional decline in nondemented older adults.

Intraindividual cognitive variability (IIV), a measure of within-person variability across cognitive measures at a single time point, is associated with mild cognitive impairment (MCI) and Alzheimer's disease (AD). Little is known regarding brain changes underlying IIV, or the relationship between IIV and functional ability. Therefore, we investigated the association between IIV and cerebral atrophy in AD-vulnerable regions and everyday functioning in nondemented older adults. 736 Alzheimer's Disease Neuroimaging Initiative (ADNI) participants (285 cognitively normal [CN]; 451 MCI) underwent neuropsychological testing and serial MRI over 2 years. Linear mixed effects models examined the association between baseline IIV and change in entorhinal cortex thickness, hippocampal volume, and everyday functioning. Adjusting for age, sex, apolipoprotein E genotype, amyloid-β positivity, and mean level of cognitive performance, higher baseline IIV predicted faster rates of entorhinal and hippocampal atrophy, as well as functional decline. Higher IIV was associated with both entorhinal and hippocampal atrophy among MCI participants but selective vulnerability of the entorhinal cortex among CN individuals. IIV was associated with more widespread medial temporal lobe (MTL) atrophy in individuals with MCI relative to CN, suggesting that IIV may be tracking advancing MTL pathologic changes across the continuum of aging, MCI, and dementia. Findings suggest that cognitive dispersion may be a sensitive marker of neurodegeneration and functional decline in nondemented older adults. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Intraindividual cognitive variability: An examination of ANAM4 TBI-MIL simple reaction time data from service members with and without mild traumatic brain injury – RETRACTION

Intraindividual cognitive variability: An examination of ANAM4 TBI-MIL simple reaction time data from service members with and without mild traumatic brain injury – RETRACTION

Intraindividual Cognitive Variability: An Examination of ANAM4 TBI-MIL Simple Reaction Time Data from Service Members with and without Mild Traumatic Brain Injury.

The Automated Neuropsychological Assessment Metrics 4 TBI-MIL (ANAM4) is a computerized cognitive test often used in post-concussion assessments with U.S. service members (SMs). However, existing evidence remains mixed regarding ANAM4's ability to identify cognitive issues following mild traumatic brain injury (mTBI). Studies typically examine ANAM4 using standardized scores and/ or comparisons to a baseline. A more fine-grained approach involves examining inconsistency within an individual's performance (i.e., intraindividual variability). Data from 237 healthy control SMs and 105 SMs within seven days of mTBI who took the ANAM4 were included in analyses. Using each individual's raw scores on a simple reaction time (RT) subtest (SRT1) that is repeated at the end of the battery (SRT2), we calculated mean raw RT and the intraindividual standard deviation (ISD) of trial-by-trial RT. Analyses investigated differences between groups in mean RT, RT variability (i.e., ISD), and change in ISD from SRT1 and SRT2. Using regression residuals to control for demographic variables, analysis of variance, and pairwise comparisons revealed the control group had faster mean RT and smaller ISD compared to the mTBI group. Furthermore, the mTBI group had a significant increase in ISD from SRT1 to SRT2, with effect sizes exceeding the minimum practical effect for comparisons of ISD in SRT2 and change in ISD from SRT1 to SRT2. While inconsistencies in performance are often viewed as test error, the results suggest intraindividual cognitive variability may be more sensitive than traditional metrics in detecting changes in cognitive function after mTBI. Additionally, the findings highlight the utility of the ANAM4's repeating a RT subtest at two points in the same session for exploring within-subject differences in performance variability. (JINS, 2018, 24, 156-162).

Cognitive Variability Predicts Incident Alzheimer's Disease and Mild Cognitive Impairment Comparable to a Cerebrospinal Fluid Biomarker.

Alzheimer's disease (AD) biomarkers are emerging as critically important for disease detection and monitoring. Most biomarkers are obtained through invasive, resource-intense procedures. A cognitive marker, intra-individual cognitive variability (IICV) may provide an alternative or adjunct marker of disease risk for individuals unable or disinclined to undergo lumbar puncture. To contrast risk of incident AD and mild cognitive impairment (MCI) associated with IICV to risk associated with well-established biomarkers: cerebrospinal fluid (CSF) phosphorylated tau protein (p-tau181) and amyloid-β 42 (Aβ42) peptide. Dispersion in cognitive performance, IICV, was estimated with a published algorithm, and included Trail Making Test A and B, Rey Auditory Verbal Learning Test (RAVLT), and the American National Adult Reading Test (ANART). CSF biomarkers were expressed as a ratio: p-tau181/Aβ42, wherein high values signified pathognomonic profiles. Logistic regression models included longitudinal data from 349 Alzheimer's Disease Neuroimaging Initiative (ADNI) participants who completed lumbar puncture. All subjects were cognitively healthy (n = 105) or diagnosed with MCI (n = 244) at baseline. We examined odds of conversion associated with baseline elevations in IICV and/or ratio of CSF p-tau181/Aβ42. When included in models alone or in combination with CSF p-tau181/Aβ42, one standard IICV unit higher was associated with an estimated odds ratio for incident AD or MCI of 2.81 (95% CI: 1.83-4.33) in the most inclusive sample, and an odds ratio of 3.41 (95% CI: 2.03-5.73) when restricted to participants with MCI. Iterative analyses suggested that IICV independently improved model fit even when individual index components were included in comparative models. These analyses provide preliminary support for IICV as a marker of incident AD and MCI. This easily-disseminated, non-invasive marker compared favorably to well-established CSF biomarkers.

RETRACTED - Intra-individual Cognitive Variability: An Examination of ANAM4 TBI-MIL Simple Reaction Time Data from Service Members with and without Mild Traumatic Brain Injury.

Objectives: The Automated Neuropsychological Assessment Metrics 4 TBI-MIL (ANAM4) is a computerized cognitive test often used in post-concussion assessments with U.S. service members (SMs). Existing evidence, however, remains mixed regarding ANAM4's ability to identify cognitive issues following mild traumatic brain injury (mTBI). Studies typically examine ANAM4 by comparing mean scores to baseline or normative scores. A more fine-grained approach involves examining inconsistency within an individual's performance. Methods: Data from a sample of 231 were healthy control SMs and 100 SMs within 7 days of mTBI who took the ANAM4 were included in analyses. We examine each individual's performance on a simple reaction time (SRT) subtest that is administered at the beginning (SRT1) and end (SRT2) of the ANAM4 battery, and calculate the standard deviation of difference scores by trial across administrations. Results: Multivariate analysis of variance and univariate analyses revealed group differences across all comparisons (p<.001) with pairwise comparisons revealing higher intra-individual variability and slower raw reaction time for the mTBI group compared with controls. Effect sizes were small though exceeded the recommended minimum practical effect size (ES>0.41). Conclusions: While inconsistencies in performance are often viewed as noise or test error, the results suggest intra-individual cognitive variability may be more sensitive than central tendency measures (i.e., comparison of means) in detecting changes in cognitive function in mTBI. Additionally, the findings highlight the utility of ANAM4's repeating a subtest at two points in a battery to explore within-subject differences in performance. (JINS, 2017, 23, 1-6).

C-54Physiological and Cognitive Intra-individual Variability are Negatively Associated

C-54Physiological and Cognitive Intra-individual Variability are Negatively Associated

A COMPARISON OF METHODS TO MEASURE INTRA-INDIVIDUAL COGNITIVE VARIABILITY IN NON-HISPANIC WHITES AND AFRICAN AMERICANS IN THE WISCONSIN REGISTRY FOR ALZHEIMER'S PREVENTION (WRAP)

Inexpensive, easily-disseminated, and reliable markers are needed to detect preclinical Alzheimer's disease (AD). Intra-individual cognitive variability (IICV) in cognitively healthy individuals, calculated as the standard deviation of cognitive scores, predicts later cognitive impairment; yet little is known about how IICV performs in groups typically underrepresented in research. Recent research suggests that incorporating the pattern or direction of discrepancies may yield stronger IICV indicators for AD risk. In this study, we compared novel approaches for estimating IICV, which considered the direction and pattern of differences (Pattern-IICV) to a previously-used simple dispersion IICV, estimating only the magnitude of variability (Dispersion-IICV). Secondly, we compared performance of the IICV indices in African Americans (AA) and non-Hispanic whites. Participants were from the Wisconsin Registry for Alzheimer's Prevention (WRAP) and included non-Hispanic whites (n=1154) and AA (n=48) with >2 study visits. IICV estimates included a previously-studied Dispersion-IICV and Pattern-informed IICVs, using either robust normed z-scores or z-scores derived from raw scores. Table 1 describes IICV estimates. IICV indices were compared across race. Associations between IICV indices and other midlife risk factors, and baseline (normal, early MCI) and later cognitive status (normal, early MCI, clinical MCI/Dementia) were examined. AAs showed significantly higher variability than whites on IICV indices. All IICV formulations predicted concurrent cognitive status; however, only Pattern-IICVs were associated with longitudinal cognitive status. See Table 2. Conversely, Dispersion-IICVs were associated with midlife AD risk factors. Comparing indices between whites and Blacks, a raw score Pattern-IICV predicted risks similarly; whereas Dispersion-IICVs appeared under-powered to detect risk in AAs. A non-invasive, easily-disseminated marker of preclinical AD would be a valuable tool to reach populations reticent to under-go procedures in academic medical centers. Overall, AAs demonstrated more cognitive variability at baseline than whites. Although, it is unclear whether IICV is detecting true elevated risk for later impairment or over-pathologizing normal dispersion in AAs’ cognitive performance. Validity checks suggest a mixed picture for the three IICVs. Pattern-IICVs hold promise for measuring risk for incident decline, whereas Dispersion-IICV was most closely associated with other midlife risk factors. Overall, IICV needs further validation, especially in underrepresented groups.

Intraindividual Cognitive Variability in Middle Age Predicts Cognitive Impairment 8-10 Years Later: Results from the Wisconsin Registry for Alzheimer's Prevention.

Intraindividual cognitive variability (IICV) has been shown to differentiate between groups with normal cognition, mild cognitive impairment (MCI), and dementia. This study examined whether baseline IICV predicted subsequent mild to moderate cognitive impairment in a cognitively normal baseline sample. Participants with 4 waves of cognitive assessment were drawn from the Wisconsin Registry for Alzheimer's Prevention (WRAP; n=684; 53.6(6.6) baseline age; 9.1(1.0) years follow-up; 70% female; 74.6% parental history of Alzheimer's disease). The primary outcome was Wave 4 cognitive status ("cognitively normal" vs. "impaired") determined by consensus conference; "impaired" included early MCI (n=109), clinical MCI (n=11), or dementia (n=1). Primary predictors included two IICV variables, each based on the standard deviation of a set of scores: "6 Factor IICV" and "4 Test IICV". Each IICV variable was tested in a series of logistic regression models to determine whether IICV predicted cognitive status. In exploratory analyses, distribution-based cutoffs incorporating memory, executive function, and IICV patterns were used to create and test an MCI risk variable. Results were similar for the IICV variables: higher IICV was associated with greater risk of subsequent impairment after covariate adjustment. After adjusting for memory and executive functioning scores contributing to IICV, IICV was not significant. The MCI risk variable also predicted risk of impairment. While IICV in middle-age predicts subsequent impairment, it is a weaker risk indicator than the memory and executive function scores contributing to its calculation. Exploratory analyses suggest potential to incorporate IICV patterns into risk assessment in clinical settings. (JINS, 2016, 22, 1016-1025).

Cognitive variability—A marker for incident MCI and AD: An analysis for the Alzheimer's Disease Neuroimaging Initiative

IntroductionThe potential of intra-individual cognitive variability (IICV) to predict incident mild cognitive impairment (MCI) or Alzheimer's disease (AD) was examined and compared to well-established neuroimaging and genetic predictors. MethodsIICV was estimated using four neuropsychological measures for n = 1324 Alzheimer's Disease Neuroimaging Initiative (ADNI) participants who were cognitively healthy or diagnosed with MCI at baseline. IICV was used to predict time to incident MCI or AD, and compared to hippocampal volume loss and APOE ε4 status via survival analysis. ResultsIn survival analyses, controlling for age, education, baseline diagonosis, and APOE ε4 status, likelihood ratio tests indicate that IICV is associated with time to cognitive status change in the full sample (P < .0001), and when the sample was restricted to individuals with MCI at baseline (P < .0001). DiscussionThese findings suggest IICV may be a low-cost, noninvasive alternative to traditional AD biomarkers.

Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) intraindividual variability in older adults: Associations with disease and mortality

Cognitive intraindividual variability (IIV), or dispersion, has been associated with pathological changes, including cognitive and functional decline. Dispersion is typically assessed with experimental cognitive measures or subtests selected from several batteries, and few studies have examined IIV from a single neuropsychological battery. Method: To address this gap, the current study examined the relationship between the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) IIV, mean cognitive performance, self-reported functioning, and death among 699 individuals between 64 and 94 years of age who were screened for neurological illness and living independently in the community. A coefficient of variation statistic served as the dispersion index and was derived by calculating the within-subject variability of the five RBANS indexes for each participant and dividing this value by the overall test battery mean. Results: Results revealed that increased dispersion and poorer mean performance simultaneously predicted self-reported memory problems. In addition, participants with elevated dispersion at baseline had increased rates of death nine years later, although this lost significance after controlling for comorbid heart disease. Cluster analysis of the higher dispersion scores revealed four distinct profile patterns that did not differ on the outcome variables. Conclusions: Elevated RBANS dispersion is a proxy of co-occurring health problems and may be a useful metric of functional decline and death within community-dwelling geriatric populations.

Intra-individual cognitive variability: An alternative to invasive Alzheimer’s disease biomarkers?

Intra-individual cognitive variability: An alternative to invasive Alzheimer’s disease biomarkers?

Midlife intra-individual cognitive variability in wrap is associated with psychometric mild cognitive impairment 2 to 8 years later

Midlife intra-individual cognitive variability in wrap is associated with psychometric mild cognitive impairment 2 to 8 years later

Neurocognitive intra-individual variability in mood disorders: effects on attentional response time distributions.

Attentional impairment is a core cognitive feature of major depressive disorder (MDD) and bipolar disorder (BD). However, little is known of the characteristics of response time (RT) distributions from attentional tasks. This is crucial to furthering our understanding of the profile and extent of cognitive intra-individual variability (IIV) in mood disorders. A computerized sustained attention task was administered to 138 healthy controls and 158 patients with a mood disorder: 86 euthymic BD, 33 depressed BD and 39 medication-free MDD patients. Measures of IIV, including individual standard deviation (iSD) and coefficient of variation (CoV), were derived for each participant. Ex-Gaussian (and Vincentile) analyses were used to characterize the RT distributions into three components: mu and sigma (mean and standard deviation of the Gaussian portion of the distribution) and tau (the 'slow tail' of the distribution). Compared with healthy controls, iSD was increased significantly in all patient samples. Due to minimal changes in average RT, CoV was only increased significantly in BD depressed patients. Ex-Gaussian modelling indicated a significant increase in tau in euthymic BD [Cohen's d = 0.39, 95% confidence interval (CI) 0.09-0.69, p = 0.011], and both sigma (d = 0.57, 95% CI 0.07-1.05, p = 0.025) and tau (d = 1.14, 95% CI 0.60-1.64, p < 0.0001) in depressed BD. The mu parameter did not differ from controls. Increased cognitive variability may be a core feature of mood disorders. This is the first demonstration of differences in attentional RT distribution parameters between MDD and BD, and BD depression and euthymia. These data highlight the utility of applying measures of IIV to characterize neurocognitive variability and the great potential for future application.