Neuroanatomical correlates of selected executive functions in middle-aged and older adults: a prospective MRI study

Neuroanatomical substrates of age-related differences in working memory and perseverative behavior were examined in a sample of healthy adults (50-81 years old). The participants, who were screened for history of neurological, psychiatric, and medical conditions known to be linked to poor cognitive performance, underwent magnetic resonance imaging (MRI) and were administered tests of working memory and perseveration. Regional brain volumes and the volume of white matter hyperintensities (WMH) were measured on magnetic resonance images. The analyses indicate that the volume of the prefrontal cortex (PFC) and the volume of white matter hyperintensities in the prefrontal region are independently associated with age-related increases in perseverative errors on the Wisconsin Card Sorting Test (WCST). When participants taking antihypertensive medication were excluded from the analysis, both the volume of the prefrontal cortex and the frontal white matter hyperintensities (FWMH) still predicted increases in perseveration. Neither reduced volume of the prefrontal cortex nor the FWMH volume was linked to age-associated declines in working memory. The volumes of the fusiform gyrus (FG) and the temporal white matter hyperintensities (TWMH) were unrelated to cognitive performance.

A Quantitative Model-Based Approach to Examining Aging Effects on Information-Integration Category Learning

Information-integration category learning was examined in older and younger adults. Accuracy results indicated that older participants learned less well than younger participants in both linear and nonlinear conditions. Model-based analyses indicated that both groups in the linear condition tended to use information integration but that later in training younger participants were more likely to do so. In contrast, the 2 groups in the nonlinear condition were equally likely to use information integration. Further analysis indicated that younger adults were more accurate than older adults when an information-integration approach was adopted, whereas fewer age-related differences were observed when a rule-based approach was used, suggesting that age can have a negative impact on information-integration category learning processes but less impact on rule-based learning.

Factor structure of a modified version of the wisconsin card sorting test: an analysis of executive deficit in Alzheimer's disease and mild cognitive impairment

In order to explore the factor structure of a modified version of the Wisconsin Card Sorting Test (mWCST) and to identify the dimensions of deficit in patients with Alzheimer's disease (AD) and mild cognitive impairment (MCI), conventional mWCST scores in 55 AD patients, 17 MCI patients, and 22 controls were subjected to factor analysis. Three factors, perseveration, inefficient sorting, and nonperseverative error, were obtained. Perseveration score was significantly poorer in both AD and MCI than in controls. By contrast, the MCI group showed significantly poorer scores on the nonperseverative error factor than did the AD patients, and the controls yielded intermediate values between the two patient groups. The perseveration factor was significantly correlated with the other estimates of executive function. This study suggested that the many mWCST scores could be reduced to three major factors, and that the perseveration score may effectively represent an aspect of executive dysfunction in AD and MCI patients.

Wisconsin Card Sorting Test performance in schizophrenia: the role of working memory

Schizophrenia typically results in reduced performance on the Wisconsin Card Sorting Test (WCST). In the current study, we used a variety of approaches to examine the role of working memory (WM) in this deficit. One approach was to examine patterns of perseverative and non-perseverative errors. A second approach involved the comparison of the standard WCST to a modified version that used visual cues to reduce demands on WM. A third approach was to quantify the impact of WM demands on performance on a trial by trial basis. Consistent with theories of WM, the schizophrenia group showed increases in both perseverative and non-perseverative errors and differences between individuals with schizophrenia and controls were largest when WM demands were high. The visual cues helped the schizophrenia group overcome the high WM demands of the test, although they did not reduce the impairment in terms of standard scoring procedures. All impairments disappeared, however, after controlling for group differences on a measure of the speed of encoding information in WM. The pattern of results supports the conclusion that WM impairment contributes to poor performance on the WCST in individuals with schizophrenia, with additional evidence that this impairment results from generalized slowing of information processing.

Mental fatigue and the control of cognitive processes: effects on perseveration and planning

We tested whether behavioural manifestations of mental fatigue may be linked to compromised executive control, which refers to the ability to regulate perceptual and motor processes for goal-directed behaviour. In complex tasks, compromised executive control may become manifest as decreased flexibility and sub-optimal planning. In the study we use the Wisconsin Card Sorting Test (WCST) and the Tower of London (TOL), which respectively measure flexibility (e.g., perseverative errors) and planning. A simple memory task was used as a control measure. Fatigue was induced through working for 2 h on cognitively demanding tasks. The results showed that compared to a non-fatigued group, fatigued participants displayed more perseveration on the WCST and showed prolonged planning time on the TOL. Fatigue did not affect performance on the simple memory task. These findings indicate compromised executive control under fatigue, which may explain the typical errors and sub-optimal performance that are often found in fatigued people.

Working memory and schizophrenia: evidence for slowed encoding

Previous studies have found impairments in working memory in individuals with schizophrenia, but have not identified the underlying information processing deficit. Because schizophrenia is associated with slowed cognitive processing, deficits on working memory tests may be due to decreased speed of encoding rather than an inability to maintain information over time. This hypothesis was examined using a Delayed Match to Sample (DMTS) Test. Task difficulty under 0-delay conditions was equated by individually establishing the stimulus presentation time needed to reach approximately 80% accuracy. Schizophrenia participants required longer presentation durations, but there were no group differences under delay conditions when performance was equated in the 0-delay condition. These results suggest that poor working memory performance in schizophrenia results from slowed encoding processes.

Behavioral evidence for working memory of sensory dimension in macaque monkeys

For animals, which lack language codes, there might be limitations in the use of abstract concepts in guiding their behavior. We trained two macaque monkeys in a computerized version of Wisconsin Card Sorting Task (WCST) with two dimensions (shape and color) to test their capability for memorizing, updating and using representation of sensory dimension. A sample had to be matched with one of three test items by either matching in color or shape. The monkeys had to find the relevant sensory dimension and its sudden changes by trial and error only based on reward and error signals. Both monkeys succeeded in more than ten shifts in the rules within a daily session. Several probe tests showed that the monkeys in fact used the dimension-based matching rules, because the rule shift was generalized from the experience of some samples to all of the others in the sample set, and because the rules were immediately applied to newly introduced samples. The frequent shifts can be overcome only with representation of the sensory dimension in working memory. These results, thus, suggest that nonhuman primates can store sensory dimension such as color and shape in working memory, dynamically update it based on the behavioral outcomes, and use it to guide behavior, despite their lack of apparent language.

Age-related differences in the course of cognitive skill acquisition: the role of regional cortical shrinkage and cognitive resources

This study examined the impact of age-related differences in regional cerebral volumes and cognitive resources on acquisition of a cognitive skill. Volumes of brain regions were measured on magnetic resonance images of healthy adults (aged 22-80). At the early stage of learning to solve the Tower of Hanoi puzzle, speed and efficiency were associated with age, prefrontal cortex volume, and working memory. A similar pattern of brain-behavior associations was observed with perseveration measured on the Wisconsin Card Sorting Test. None of the examined structural brain variables were important at the later stages of skill acquisition. When hypertensive participants were excluded, the effect of prefrontal shrinkage on executive aspects of performance was no longer significant, but the effect of working memory remained.