Establishing the base rate of performance invalidity in a clinical electrical injury sample: Implications for neuropsychological test performance.

Objective: The base rate of neuropsychological performance invalidity in electrical injury, a clinically-distinct and frequently compensation-seeking population, is not well established. This study determined the base rate of performance invalidity in a large electrical injury sample, and examined patient characteristics, injury parameters, and neuropsychological test performance based on validity status.Method: This cross-sectional study included data from 101 patients with electrical injury consecutively referred for post-acute neuropsychological evaluation. Eighty-five percent of the sample was compensation-seeking. Multiple performance validity tests (PVTs) were administered as part of standard clinical evaluation. For patients with four or more PVTs, valid performance was operationalized as less than or equal to one PVT failure and invalid performance as two or more failures.Results: Frequency analysis revealed 66% (n = 67) had valid performance while 29% (n = 29) demonstrated probable invalid performance; the remaining 5% (n = 5) had indeterminate validity. No significant differences in demographics or injury parameters emerged between validity groups (0 vs. 1 vs. ≥2 PVT failures). In contrast, the electrical injury group with invalid performance performed significantly worse across tests of processing speed and executive abilities than those with valid performance (ps< .05, ηp2 = .19-.25).Conclusions: The current study is the first to establish the base rate of neuropsychological performance invalidity in electrical injury survivors using empirical methods and current practice standards. Patient and clinical variables, including compensation-seeking status, did not differ between validity groups; however, neuropsychological test performance did, supporting the need for multi-method, objective performance validity assessment.

The relationship between neuropsychological dispersion, processing speed and memory after electrical injury.

Introduction: Previous studies of neuropsychological performance in electrical injury (EI) patients have produced evidence of deficits in various cognitive domains, but studies have yet to investigate relationships among performance in cognitive domains post-EI. This study examined whether dispersion among neuropsychological test scores was associated with injury parameters and neuropsychological performance in EI patients. Additionally, we examined whether dispersion, processing speed and/or executive abilities explain variance in episodic verbal and visual memory performance among EI patients.Method: Data from 52 post-acute EI patients undergoing outpatient evaluation with objectively-verified valid neuropsychological test performance were examined. Tests included measures of verbal and visual memory, processing speed, and executive functioning. Dispersion was calculated from executive functioning and processing speed scores.Results: Dispersion was not related to mean performance or injury characteristics, but was significantly negatively correlated with performance on a test of processing speed, suggesting that increased dispersion is associated with reduced cognitive efficiency post-EI. Delayed visual memory was related to both dispersion scores and processing speed. Stepwise regression equations predicting delayed memory determined that processing speed most significantly predicted delayed visual memory, even after controlling for immediate visual memory. No significant relationships emerged between verbal memory and non-memory neuropsychological scores.Conclusions: This is the first study to examine neuropsychological dispersion and relationships among domains of cognitive functioning in EI. Current results suggested that neuropsychological dispersion is not a marker of general functioning or severity of injury in EI patients, but may represent more specific processing speed abilities. Processing speed predicts delayed visual memory performance in EI patients, which should be considered in interpreting test scores during evaluations.

Examination of the Minnesota Multiphasic Personality Inventory-2-Restructured Form (MMPI-2-RF) validity and substantive scales in patients with electrical injury.

Objective: Electrical injury (EI) is a distinct subtype of traumatic injury that often results in a unique constellation of cognitive sequelae and unusual sensory experiences due to peripheral nervous system injury that are uncommon in general medical/neurological populations and have been unexplored with the Minnesota Multiphasic Personality Inventory-2-Restructured Form (MMPI-2-RF). Method: This study examined performance patterns on MMPI-2-RF validity and substantive scales among 62 EI patients who underwent neuropsychological evaluation, of which 46 demonstrated valid symptom reporting and neurocognitive test performance via multiple independent validity indicators and were retained for analysis. Results: Valid EI patients scored significantly higher than the MMPI-2-RF normative sample on several validity scales with the largest effect sizes on F-r (Infrequent Responses), Fs (Infrequent Somatic Responses), FBS-r (Symptom Validity), and RBS (Response Bias), and ≥33% obtaining elevated scores on these scales per standard interpretive criteria. Review of item content on these scales revealed several reflect disturbances in sensation, physical functioning, and/or cognition that are not infrequent in this population. Further, MMPI-2-RF clinical profiles did not reveal generalized distress or noncredible over-reporting. Rather, similar to the MMPI-2, valid EI patients had a specific pattern related to physical/sensory symptoms and reduced positive emotions with elevations on restructured clinical (RC) scale 1 (somatic complaints), somatic/cognitive specific problem scales, and low positive emotions (RC2). Conclusions: Elevations on some MMPI-2-RF validity scale may capture some degree of actual EI sequela that neuropsychologists need to consider to prevent erroneously concluding that a credible EI patient is over-reporting when s/he is reporting bona fide, EI-related symptoms.

Neurocognitive performance in drug-dependent males and females with posttraumatic stress disorder symptoms.

Sex differences in neurobiological mechanisms of substance dependence are well documented but studies of sex differences in associated neurocognitive deficits have produced inconsistent results. Posttraumatic stress disorder (PTSD) is comorbid with substance dependence and frequently affects neurocognition. Thus, we investigated the effects of sex and PTSD symptoms on sustained attention and inhibition abilities among 126 female and 297 male substance-dependent individuals (SDIs) using the Immediate Memory Test (IMT). Females with significant PTSD (PTSD+) symptoms demonstrated significantly impaired IMT performance relative to other participants. These results represent progress in efforts to delineate sex-specific risk factors for neurocognitive deficits among SDIs.

Flexible neural mechanisms of cognitive control within human prefrontal cortex.

A major challenge in research on executive control is to reveal its functional decomposition into underlying neural mechanisms. A typical assumption is that this decomposition occurs solely through anatomically based dissociations. Here we tested an alternative hypothesis that different cognitive control processes may be implemented within the same brain regions, with fractionation and dissociation occurring on the basis of temporal dynamics. Regions within lateral prefrontal cortex (PFC) were examined that, in a prior study, exhibited contrasting temporal dynamics between older and younger adults during performance of the AX-CPT cognitive control task. The temporal dynamics in younger adults fit a proactive control pattern (primarily cue-based activation), whereas in older adults a reactive control pattern was found (primarily probe-based activation). In the current study, we found that following a period of task-strategy training, these older adults exhibited a proactive shift within a subset of the PFC regions, normalizing their activity dynamics toward young adult patterns. Conversely, under conditions of penalty-based monetary incentives, the younger adults exhibited a reactive shift some of the same regions, altering their temporal dynamics toward the older adult baseline pattern. These experimentally induced crossover patterns of temporal dynamics provide strong support for dual modes of cognitive control that can be flexibly shifted within PFC regions, via modulation of neural responses to changing task conditions or behavioral goals.

Age-related changes in neural activity during performance matched working memory manipulation.

A long-standing assumption in the cognitive aging literature is that performance on working memory (WM) tasks involving serial recall is relatively unaffected by aging, whereas tasks that require the rearrangement of items prior to recall are more age-sensitive. Previous neuroimaging studies of WM have found age-related increases in neural activity in frontoparietal brain regions during simple maintenance tasks, but few have examined whether there are age-related differences that are specific to rearranging WM items. In the current study, older and younger adults' brain activity was monitored using functional magnetic resonance imaging (fMRI) as they performed WM tasks involving either maintenance or manipulation (letter-number sequencing). The paradigm was developed so that performance was equivalent across age groups in both tasks, and the manipulation condition was not more difficult than the maintenance condition. In younger adults, manipulation-related increases in activation occurred within a very focal set of regions within the canonical brain WM network, including left posterior prefrontal cortex and bilateral inferior parietal cortex. In contrast, older adults showed a much wider extent of manipulation-related activation within this WM network, with significantly increased activity relative to younger adults found within bilateral PFC. The results suggest that activation and age-differences in lateral PFC engagement during WM manipulation conditions may reflect strategy use and controlled processing demands rather than reflect the act of manipulation per se.

Cognitive control, goal maintenance, and prefrontal function in healthy aging.

Cognitive control impairments in healthy older adults may partly reflect disturbances in the ability to actively maintain goal-relevant information, a function that depends on the engagement of lateral prefrontal cortex (PFC). In 2 functional magnetic resonance imaging studies, healthy young and older adults performed versions of a task in which contextual cues provide goal-relevant information used to bias processing of subsequent ambiguous probes. In Study 1, a blocked design and manipulation of the cue-probe delay interval revealed a generalized pattern of enhanced task-related brain activity in older adults but combined with a specific delay-related reduction of activity in lateral PFC regions. In Study 2, a combined blocked/event-related design revealed enhanced sustained (i.e., across-trial) activity but a reduction in transient trial-related activation in lateral PFC among older adults. Further analyses of within-trial activity dynamics indicated that, within these and other lateral PFC regions, older adults showed reduced activation during the cue and delay period but increased activation at the time of the probe, particularly on high-interference trials. These results are consistent with the hypothesis that age-related impairments in goal maintenance abilities cause a compensatory shift in older adults from a proactive (seen in young adults) to a reactive cognitive control strategy.

Deterioration of visual-perceptual organization ability in Alzheimer's disease.

Although deterioration of higher-order visual information processing abilities occurs in Alzheimer's disease (AD), few cross-sectional or longitudinal studies have systematically examined this deficit. The performance of 135 patients with probable AD and 97 matched normal control (NC) participants were compared on a structured test of perceptual organization ability, the Hooper Visual Organization Test (VOT). Both the standard VOT score and a derived score that corrected for anomia were significantly lower for AD patients than for NC participants, but neither score was particularly effective at distinguishing between the groups. The derived VOT score proved to be a more effective measure of visuospatial functioning than the standard VOT score as it loaded with other visuospatial tests in a principal components analysis while the standard score loaded with language tests. The VOT was sensitive to severity of dementia in the AD patients. Longitudinal assessment of 37 of the AD patients and 46 NC participants revealed significant decline over one year in the VOT scores of AD patients, but not in those of NC participants. These results indicate that higher-order visual information processing is impaired in patients with AD and gradually deteriorates with disease progression. This deficit may not be a particularly salient early marker of the disease, but it may be useful in tracking disease course.

Effects of environmental support and strategy training on older adults' use of context.

Age-related cognitive differences may be due, in part, to difficulties using task-relevant context in a proactive manner. Two studies evaluated different methods for increasing older adults' use of context in the AX-Continuous Performance Task (H. E. Rosvold, A. F. Mirsky, I. Sarason, E. D. Bransome, & L. H. Beck, 1956), which evaluates components of context processing. The results suggest that (a) age differences in the use of context are not due to reduced access to cue information, (b) directed strategy training made older adults' context processing performance more like that of young adults, and (c) similar performance changes could be observed with less directed instruction and extended practice. These results suggest that age-related differences in context processing can be ameliorated by directed strategy training or extended practice.

Word association in early Alzheimer's disease.

The hypothesis that Alzheimer's disease (AD) degrades semantic representations predicts that AD qualitatively alters spontaneous thoughts. In two experiments contrasting free associations to words with strong (e.g., bride-groom) versus weak (e.g., body-leg) associates participants with AD produced less common responses (e.g., bride-pretty) than normal controls but only for words with strong associations, and only on the first (but not on second or third) association response. Furthermore, all participants produced fewer semantically related responses to words with weak associates. Because strong associations should be retrieved more easily than weak associations these results are problematic for retrieval-based accounts of AD. Instead we propose that AD entails a semantic deficit, and that strong associations involve more semantic processing than weak associations (in all speakers).