Justin E. Karr

The Neuropsychological Outcomes of Concussion: A Systematic Review of Meta-Analyses on the Cognitive Sequelae of Mild Traumatic Brain Injury

UNLABELLED Mild Traumatic Brain Injury (mTBI), also known as concussion, has become a growing public health concern, prevalent in both athletic and military settings. Many researchers have examined post-mTBI neuropsychological outcomes, leading to multiple meta-analyses amalgamating individual study results. OBJECTIVE Considering the plethora of meta-analytic findings, the next logical step stands as a systematic review of meta-analyses, effectively reporting key moderators that predict post-mTBI neuropsychological outcomes. METHOD A systematic review of reviews yielded 11 meta-analyses meeting inclusion criteria (i.e., English-language systematic reviews/meta-analyses covering post-mTBI observational cognitive research on late adolescents/adults), with their findings qualitatively synthesized based on moderator variables (i.e., cognitive domain, time since injury, past head injury, participant characteristics, comparison group, assessment technique, and persistent symptoms). RESULTS The overall effect sizes ranged for both general (range: .07-.61) and sports-related mTBI (range: .40-.81) and differed both between and within cognitive domains, with executive functions appearing most sensitive to multiple mTBI. Cognitive domains varied in recovery rates, but overall recovery occurred by 90 days postinjury for most individuals and by 7 days postinjury for athletes. Greater age/education and male gender produced smaller effects sizes, and high school athletes suffered the largest deficits post-mTBI. Control-group comparisons yielded larger effects than within-person designs, and assessment techniques had limited moderating effects. CONCLUSIONS Overall, meta-analytic review quality remained low with few studies assessing publication or study quality bias. Meta-analyses consistently identified adverse acute mTBI-related effects and fairly rapid symptom resolution. Future meta-analyses should better operationally define cognitive constructs to produce more consistent effect estimates across domains.

An empirical comparison of the therapeutic benefits of physical exercise and cognitive training on the executive functions of older adults: a meta-analysis of controlled trials.

UNLABELLED A robust body of aging-related research has established benefits of both physical exercise (PE) and cognitive training (CT) on executive functions related to the activities of daily living of older adults; however, no meta-analysis has compared these treatments. OBJECTIVE The current quantitative review involved a comparison of the overall effect sizes of PE and CT interventions on executive functions (Morris, 2008; pre-post-controlled effect size: d(ppc)), while also exploring contextual moderators of treatment outcomes. METHOD A systematic review identified 46 studies (23 PE, 21 CT, and 2 both) meeting inclusion criteria (i.e., controlled interventions, executive-related outcomes, mean ages 65+, information to calculate d(ppc)). RESULTS The weighted mean dppc values came to 0.12 (p < .01) for PE and 0.24 (p < .01) for CT. Treatment effects differed based on executive constructs for CT, with problem solving presenting the highest d(ppc) (0.47, p < .01). Notably, PE produced similar effect sizes across distinct executive functions. Treatment characteristics (e.g., session length/frequency) did not predict effect sizes. CT had a significant benefit on healthy participants (0.26, p < .01), but cognitively impaired samples did not experience a significant effect. CONCLUSIONS Both treatments improved executive functions, but CT presented a potential advantage at improving executive functions. Improvements in executive functions differed depending on construct for CT, whereas each construct produced similar, modest effect sizes for PE. Publication bias and study quality variability potentially bias these conclusions, as lower quality studies likely produced inflated effect sizes.

Blast-Related Mild Traumatic Brain Injury: A Bayesian Random-Effects Meta-Analysis on the Cognitive Outcomes of Concussion among Military Personnel

Throughout their careers, many soldiers experience repeated blasts exposures from improvised explosive devices, which often involve head injury. Consequentially, blast-related mild Traumatic Brain Injury (mTBI) has become prevalent in modern conflicts, often occuring co-morbidly with psychiatric illness (e.g., post-traumatic stress disorder [PTSD]). In turn, a growing body of research has begun to explore the cognitive and psychiatric sequelae of blast-related mTBI. The current meta-analysis aimed to evaluate the chronic effects of blast-related mTBI on cognitive performance. A systematic review identified 9 studies reporting 12 samples meeting eligibility criteria. A Bayesian random-effects meta-analysis was conducted with cognitive construct and PTSD symptoms explored as moderators. The overall posterior mean effect size and Highest Density Interval (HDI) came to d = −0.12 [−0.21, −0.04], with executive function (−0.16 [−0.31, 0.00]), verbal delayed memory (−0.19 [−0.44, 0.06]) and processing speed (−0.11 [−0.26, 0.01]) presenting as the most sensitive cognitive domains to blast-related mTBI. When dividing executive function into diverse sub-constructs (i.e., working memory, inhibition, set-shifting), set-shifting presented the largest effect size (−0.33 [−0.55, −0.05]). PTSD symptoms did not predict cognitive effects sizes, βPTSD = −0.02 [−0.23, 0.20]. The results indicate a subtle, but chronic cognitive impairment following mTBI, especially in set-shifting, a relevant aspect of executive attention. These findings are consistent with past meta-analyses on multiple mTBI and correspond with past neuroimaging research on the cognitive correlates of white matter damage common in mTBI. However, all studies had cross-sectional designs, which resulted in universally low quality ratings and limited the conclusions inferable from this meta-analysis.

Longitudinal applications of a behavioral screener of executive functioning: assessing factorial invariance and exploring latent growth.

This study included a replicated derivation of a behavioral screener for executive functions among children, longitudinal invariance analyses to evaluate measurement reliability across time, and latent growth modeling of 4 executive functions: problem solving, attentional control, behavioral control, and emotional control. The sample included 1,237 (52% female) participants age 6 to 11 years. Participants were tracked longitudinally for 3 years with 5 assessment waves, and new participants were recruited at each wave to compensate for attrition. As predicted, the 4-factor model was successfully replicated, with longitudinal invariance newly confirmed. These findings support this screener as a reliable childhood measure for executive functions, and latent growth modeling identified predictive qualities of gender and age on levels and changes in these constructs.

Executive functions and intraindividual variability following concussion.

The long-term outcomes of executive functions and intraindividual variability (IIV; i.e., trial-to-trial or across-task variability in cognitive performance) following concussion are unclear due to inconsistent and limited research findings, respectively. Objective: Responding to these gaps in scientific understanding, the current study aimed to assess the utility of both executive functions and IIV at predicting concussion history. Method: Altogether 138 self-identified athletes (Mage = 19.9 ± 1.91 years, 60.8% female, 19.6% with one concussion, 18.1% with two or more concussions) completed three executive-related cognitive tasks (i.e., n-back, go/no-go, global–local). Ordinal logistic regression analyses examined the joint effect of person-mean and IIV as predictors of concussion status. Results: Only mean response time for the global–local task predicted the number of past concussions, while no IIV variables reached unique significance. Conclusions: IIV research on concussion remains limited; however, the preliminary results do not indicate any additional value of IIV indices above mean performances at predicting past concussion. For executive functions, shifting appears most sensitive at detecting concussion group differences, with past researchers identifying post concussion impairment in attentional processing.

Using Multivariate Base Rates to Interpret Low Scores on an Abbreviated Battery of the Delis–Kaplan Executive Function System

Objective Executive function consists of multiple cognitive processes that operate as an interactive system to produce volitional goal-oriented behavior, governed in large part by frontal microstructural and physiological networks. Identification of deficits in executive function in those with neurological or psychiatric conditions can be difficult because the normal variation in executive function test scores, in healthy adults when multiple tests are used, is largely unknown. This study addresses that gap in the literature by examining the prevalence of low scores on a brief battery of executive function tests. Method The sample consisted of 1,050 healthy individuals (ages 16-89) from the standardization sample for the Delis-Kaplan Executive Function System (D-KEFS). Seven individual test scores from the Trail Making Test, Color-Word Interference Test, and Verbal Fluency Test were analyzed. Results Low test scores, as defined by commonly used clinical cut-offs (i.e., ≤25th, 16th, 9th, 5th, and 2nd percentiles), occurred commonly among the adult portion of the D-KEFS normative sample (e.g., 62.8% of the sample had one or more scores ≤16th percentile, 36.1% had one or more scores ≤5th percentile), and the prevalence of low scores increased with lower intelligence and fewer years of education. Conclusions The multivariate base rates (BR) in this article allow clinicians to understand the normal frequency of low scores in the general population. By use of these BRs, clinicians and researchers can improve the accuracy with which they identify executive dysfunction in clinical groups, such as those with traumatic brain injury or neurodegenerative diseases.

Cross-cultural validation of a behavioral screener for executive functions: Guidelines for clinical use among Colombian children with and without ADHD.

Garcia-Barrera, Kamphaus, and Bandalos (2011) derived a 25-item executive functioning screener from the Behavior Assessment System for Children (BASC), measuring 4 latent executive constructs: problem solving, attentional control, behavioral control, and emotional control. The current study included a cross-cultural examination of this screener in Colombian children with and without attention-deficit/hyperactivity disorder (ADHD). BASC teacher ratings were collected for Colombian children ages 6-11 years (848 healthy children [53% boys] and 155 children with ADHD [76% boys]). To examine the psychometric properties of the screener, a multistep procedure was implemented, including (a) confirmatory factor analysis (CFA) and factorial invariance testing across gender, age group (6-8 years, 9-11 years), and ADHD status to replicate and extend the original derivation; (b) item response theory (IRT) analysis to evaluate the information provided by individual items; and (c) given IRT results, a repeated CFA and invariance testing after the exclusion of 1 item from the problem-solving factor. The 24-item 4-factor model fit was adequate for controls and for ADHD participants. Results support the use of the 24-item executive functioning screener in a cross-cultural context. In turn, in supplemental material, normative data for the Colombian sample are reported along with bilingual guidelines (i.e., Spanish/English) for implementing the screener in clinical practice. Even though the screener is useful when examining executive functions, it was not designed as a diagnostic measure for developmental disorders such as ADHD; as such, it should only inform about status of executive functioning.

Examining Executive Functioning Using the Behavior Assessment System for Children (BASC)

As it was suggested by Strayhorn (1993) 2 decades ago, one of the most limiting constraints of our scientific progress in measuring human behavior has been our inability to produce valid and reliable instruments, despite our technological developments. These difficulties have been made readily apparent when trying to measure psychological constructs. In the philosophy of science, a construct has been defined as a product of the mind rather than independent of it. In other words, a construct is an “ideal object” of science as oppose to a “real” one. We have agreed in psychology that as constructs represent our ideas, they are not directly observable, and it is via our observations of their outcomes that we attempt to estimate and quantify them. The self-regulatory ability we call executive function in neuropsychology is one of the best examples of such elusive constructs (Jurado & Rosselli, 2007). Thus, an underlying assumption of this chapter is that executive functions emerge as outcomes of multiple interactions between cognitive and emotional control processes. These processes are mediated by basic connections within and between key neural nodes, involved in rule setting and organization of internal representations. The ultimate goal of these interactions is to produce volitional, purposeful, and efficient guided behavior (Garcia-Barrera, 2012).

When does cognitive decline begin? A systematic review of change point studies on accelerated decline in cognitive and neurological outcomes preceding mild cognitive impairment, dementia, and death

Older adults who ultimately develop dementia experience accelerated cognitive decline long before diagnosis. A similar acceleration in cognitive decline occurs in the years before death as well. To evaluate preclinical and terminal cognitive decline, past researchers have incorporated change points in their analyses of longitudinal data, identifying point estimates of how many years prior to diagnosis or death that decline begins to accelerate. The current systematic review aimed to summarize the published literature on preclinical and terminal change points in relation to mild cognitive impairment (MCI), dementia, and death, identifying the order in which cognitive and neurological outcomes decline and factors that modify the onset and rate of decline. A systematic search protocol yielded 35 studies, describing 16 longitudinal cohorts, modeling change points for cognitive and neurological outcomes preceding MCI, dementia, or death. Change points for cognitive abilities ranged from 3–7 years prior to MCI diagnosis, 1–11 years prior to dementia diagnosis, and 3–15 years before death. No sequence of decline was observed preceding MCI or death, but the following sequence was tentatively accepted for Alzheimer’s disease: verbal memory, visuospatial ability, executive functions and fluency, and last, verbal IQ. Some of the modifiers of the onset and rate of decline examined by previous researchers included gender, education, genetics, neuropathology, and personality. Change point analyses evidence accelerated decline preceding MCI, dementia, and death, but moderators of the onset and rate of decline remain ambiguous due to between-study modeling differences, and coordinated analyses may improve comparability across future studies.

Advanced clinical interpretation of the Delis-Kaplan Executive Function System: multivariate base rates of low scores

Abstract Objective: Multivariate base rates allow for the simultaneous statistical interpretation of multiple test scores, quantifying the normal frequency of low scores on a test battery. This study provides multivariate base rates for the Delis-Kaplan Executive Function System (D-KEFS). Method: The D-KEFS consists of 9 tests with 16 Total Achievement scores (i.e. primary indicators of executive function ability). Stratified by education and intelligence, multivariate base rates were derived for the full D-KEFS and an abbreviated four-test battery (i.e. Trail Making, Color-Word Interference, Verbal Fluency, and Tower Test) using the adult portion of the normative sample (ages 16–89). Results: Multivariate base rates are provided for the full and four-test D-KEFS batteries, calculated using five low score cutoffs (i.e. ≤25th, 16th, 9th, 5th, and 2nd percentiles). Low scores occurred commonly among the D-KEFS normative sample, with 82.6 and 71.8% of participants obtaining at least one score ≤16th percentile for the full and four-test batteries, respectively. Intelligence and education were inversely related to low score frequency. Conclusions: The base rates provided herein allow clinicians to interpret multiple D-KEFS scores simultaneously for the full D-KEFS and an abbreviated battery of commonly administered tests. The use of these base rates will support clinicians when differentiating between normal variations in cognitive performance and true executive function deficits.