Peter J. Houx

Stroop interference: aging effects assessed with the stroop color-word test

A large, cross-sectional aging investigation of performance on the Stroop Color-Word Test (SCWT) was carried out. Subjects were 247 volunteers, ages 20-80 in seven age levels. Although all subjects thought themselves to be normal and healthy, a post hoc division could be made on the basis of biological life events (BLE). BLE are mild biological or environmental factors, such as repeated experiences of general anesthesia, that can hamper optimal brain functioning. Apart from the anticipated age effects, performance was poorer in subjects who had experienced one or more BLE: The slowing due to BLE was comparable to the effect of age, especially on the task involving language interference in color-naming. Education had a significant effect on performance: More highly educated subjects performed better than less educated subjects. No sex differences were observed. These findings replicate observations made with other tests in parallel studies. They are also in line with several other studies reporting interactions between the effects of aging and physical fitness. This study questions some of the validity of cognitive aging research, as our data suggest that screening for BLE as age-extrinsic factors in nondiseased subjects can reduce many of the performance deficits usually ascribed to aging per se.

Aerobic capacity and cognitive performance in a cross-sectional aging study.

In a population unselected for aerobic fitness status, aerobic fitness (VO2max) and its interaction with age were used to predict performance on several cognitive measures known to be affected by chronological age. It was hypothesized that, in particular, cognitively demanding tasks would be sensitive to aerobic capacity. Healthy subjects between 24 and 76 yr of age (N = 132) were recruited from a larger study into determinants of cognitive aging (Maastricht Aging Study-MAAS). All participants took part in a submaximal bicycle ergometer protocol and an extensive neurocognitive examination, including tests of intelligence, verbal memory, and simple and complex cognitive speed. Participants engaged more hours a week in aerobic sports and felt healthier than the nonparticipants of the same age did. No group differences were found in the basic anthropometric characteristics height, weight, and BMI. Two of four subtasks that reflect complex cognitive speed (Stroop color/word interference and Concept Shifting Test) showed main and interaction effects with age of aerobic capacity in a hierarchical regression analysis, accounting for up to 5% of variance in parameter score after correction for age, sex, and intelligence main effects. These findings fit well within a moderator model of aerobic fitness in cognitive aging. They add to the notion that aerobic fitness may selectively and age-dependently act on cognitive processes, in particular those that require relatively large attentional resources.

Mental work demands protect against cognitive impairment: MAAS prospective cohort study.

Little is known about whether persons with mentally demanding jobs are protected against cognitive impairment and whether this association is independent of intellectual abilities and other confounders. Longitudinal data from the Maastricht Aging Study (MAAS) were used to examine this association. After the 1993-1995 baseline examination, there was a first 3-year follow-up examination (1996-1998) among 630 men and women, aged 50 to 80, who exhibited no cognitive impairment at baseline. Persons with mentally demanding jobs had lower risks of developing cognitive impairment during follow-up (36 cases), compared with persons without such jobs (odds ratio = 0.79; 95% confidence interval: 0.65-0.96). About 1.5% of the persons with high mental work demands developed impairment compared to 4% of the persons with few work demands. The protective effect was independent of intellectual abilities and other confounders. Our findings provide evidence that continued and potentially modifiable mental stimulation during adult life may protect men and women against cognitive impairment.

Testing cognitive function in elderly populations: the PROSPER study

Objectives: For large scale follow up studies with non-demented patients in which cognition is an endpoint, there is a need for short, inexpensive, sensitive, and reliable neuropsychological tests that are suitable for repeated measurements. The commonly used Mini-Mental-State-Examination fulfils only the first two requirements. Methods: In the PROspective Study of Pravastatin in the Elderly at Risk (PROSPER), 5804 elderly subjects aged 70 to 82 years were examined using a learning test (memory), a coding test (general speed), and a short version of the Stroop test (attention). Data presented here were collected at dual baseline, before randomisation for active treatment. Results: The tests proved to be reliable (with test/retest reliabilities ranging from acceptable (r=0.63) to high (r=0.88) and sensitive to detect small differences in subjects from different age categories. All tests showed significant practice effects: performance increased from the first measurement to the first follow up after two weeks. Conclusion: Normative data are provided that can be used for one time neuropsychological testing as well as for assessing individual and group change. Methods for analysing cognitive change are proposed.

Rigorous health screening reduces age effect on memory scanning task

Eighty subjects participated in a study with five age groups (20, 30, 40, 50, and 60 years). Forty subjects showed evidence of factors related to brain dysfunction (risk factors). Their performance on a Sternberg-type memory scanning task was assessed. Age-related slowing of virtually all aspects of the memory scanning process was observed in the healthy group. However, the effect of the presence of risk factors was larger than that of biological age. The results of the present study make a reasonable case for the view that many age effects reported in the literature can be largely explained by suboptimal brain functioning, i.e., by other factors than aging per se.

Predictors of attrition in a longitudinal cognitive aging study: the Maastricht Aging Study (MAAS).

A large sample of older participants of the Maastricht Aging Study (MAAS) were compared to drop-outs at the 3-year follow-up with respect to socio-demographic, health, and cognitive characteristics. In addition, the impact of selective drop-out on measures of cognitive change was examined. To this end, hypothetical scores were estimated for drop-outs by using single and multiple imputation methods. Of the initial sample of 539 subjects, aged 49 years and older at baseline, 116 (22 %) did not return for the follow-up (n = 32 had died, n = 84 refused participation). Drop-outs who refused to participate in the follow-up were more often women, had lower educational levels, and had lower baseline scores on neurocognitive tests. Follow-up drop-outs who had died were more often men, older, and had a poorer performance on cognitive tests than the follow-up participants. Although follow-up participants and drop-outs differed in terms of socio-demographic and cognitive characteristics, attrition appeared to have little effect on the estimates of cognitive change.

Effect of test duration on age-related differences in Stroop interference

The effect of test duration on age-related differences in Stroop interference was assessed in a large cross-sectional study involving 429 healthy subjects in four age groups (25-35 years, 40-50 years, 55-65 years, 70-80 years). The results show a clear effect of test duration on Stroop interference. The Stroop Color Word Test was run in two parts. The young group performed the first part relatively rapidly but became slower in the second part, whereas the old group showed the reverse effect. The two middle-aged groups did not show differences between the first and second parts of the test. The results are interpreted in terms of a deficit in response inhibition by a controlled processing strategy. A psychological interpretation of the study findings in terms of increased cautiousness appears less probable. The first part of the test, that is, an abridged version of the test, may prove superior to the regular version for both clinical and research purposes.

Engaged lifestyle and cognitive function in middle and old-aged, non-demented persons: a reciprocal association?

Summary. Some studies have shown that cognitive function is positively affected by an engaged and active lifestyle. However, a recent study found evidence for an opposite causal direction, i.e., persons with good cognitive function more often start to engage in leisure-time activities. Here, we longitudinally examine the causal direction of the association between an engaged lifestyle and cognitive function in middle and old-aged Dutch men and women.    The participants in the prospective cohort study “Maastricht Aging Study” (MAAS) were recruited from a register of 15 family practices in the South of the Netherlands. There were 830 non-demented men and women, aged 49 to 81 in 1993–1995 (baseline phase). They were re-examined three years later (follow-up phase). During both phases, all persons reported on their participation in mental, social, and physical activities. Six separate neuropsychological tests, including the Mini-Mental State Examination, were used to define cognitive function at baseline and follow-up.    All three activities measured were negatively related to cognitive decline between both phases. Effects were moderate, but consistent. Persons participating in all three activities were particularly protected against longitudinal decline. Furthermore, persons with the best baseline cognitive performance were more likely to increase their number of activities during follow-up compared with persons with the poorest scores.    In summary, an engaged lifestyle and cognitive function mutually influence each other in middle and old aged, non-demented persons. This reciprocal association is characterized by simultaneous positive effects of leisure-time activities and good cognitive function on cognitive function and leisure-time activities, respectively. This reciprocal association may create a self-reinforcing, beneficial or adverse life-course in middle and old age.Zusammenfassung. Verschiedene Untersuchungen haben ergeben, dass ein engagierter Lebensstil die kognitive Funktion positiv beeinflusst. Jedoch, eine rezente Untersuchung hat eine entgegengesetzte kausale Richtung dargestellt, d.h. dass Personen, die gut kognitiv funktionieren, häufiger und früher Freizeitaktivitäten entwickeln. In dieser Studie haben wir den kausalen Zusammenhang zwischen einem aktiven Lebensstil und der kognitiven Funktion bei älteren und alten niederländischen Männern und Frauen erforscht.   Für diese prospektive Kohorten-Untersuchung „Maastricht Aging Study (MAAS)“ entnahmen wir die Teilnehmernamen einem ärztlichen Register von 15 Praxen im Süden der Niederlande. In den Jahren 1993–1995 untersuchten wir 830 nicht-demente Männer und Frauen im Altersbereich von 49–81 Jahren (erste Phase). Nach drei Jahren wurde die Untersuchung wiederholt (zweite Phase). In beiden Phasen wurden die Personen um ihre mentalen, sozialen und physischen Aktivitäten befragt. Damit das kognitive Funktionieren in der ersten und zweiten Phase festgestellt werden konnte, verwendeten wir sechs unterschiedliche neuropsychologische Tests, einschließlich der Mini Mental State Examination.    Die drei untersuchten Aktivitäten beeinträchtigten, jede für sich die kognitive Leistung zwischen den beiden Phasen. Die Effekte waren zwar bescheiden, aber konsistent. Die Personen, die alle drei Aktivitäten ausübten, waren besonders vor kognitiver Beeinträchtigung geschützt. Die Personen, die ihre Aktivitäten zwischen der ersten und zweiten Phase erweitern, waren auch diejenigen, die in der ersten Phase am besten kognitiv funktionierten.    Kurz gefasst, ein aktiver Lebensstil und die kognitive Funktion beeinflussen sich bei nicht dementen Personen mittleren und höheren Alters gegenseitig und im positiven Sinne. Diese reziproke Assoziation wird durch simultane, positive Effekte von Freizeitaktivitäten auf die kognitive Funktion einerseits, und von der kognitiven Funktion auf die Freizeitaktivitäten andererseits charakterisiert. Diese reziproke Assoziation kann bewirken, dass sich – sich selbst verstärkend – ein positiver oder aber ungünstiger Lebensverlauf in mittlerem und höherem Alter entwickelt.

Mild Hearing Impairment Can Reduce Verbal Memory Performance in a Healthy Adult Population

We studied to what extent immediate and delayed recall in an auditory verbal learning paradigm was affected by basic information processing speed (digit copying) and hearing acuity (average hearing acuity at 1, 2 and 4 KHz at the better ear). A group of 453 individuals in the age between 23 and 82 years with no overt hearing pathology was recruited from a larger study of cognitive aging (Maastricht Aging Study, MAAS). After controlling for age, sex, educational level, and processing speed it was found that a mild to moderate hearing loss predicted lower verbal memory performance. Auditory administered verbal memory tests can underestimate true memory performance, particularly in older individuals with unknown hearing status.

Education and agerelated cognitive decline; the contribution of mental workload.

Few studies have examined why, in most reports, low education is related to accelerated cognitive decline in middle and old age. Intellectual abilities - whether or not innate - and the mental stimulation provided by the educational process itself are frequently hypothesized to be the most relevant mechanisms. Work characteristics, such as the mental workload of a job, may be another mechanism, as these may also be related to educational level. Moreover, these are more amenable to modification than intellectual abilities. First longitudinal data from the Maastricht Aging Study (MAAS) among 708 men and women aged 50 to 80 in 1993-1995 were used to quantify the contribution of adult mental workload to the associationbetween educational level and age-related cognitive decline. In the 3-year follow-up, persons with a low educational level experienced more decline in cognitive function (information processing speed, memory, and general cognitive function according to the Mini-Mental State Examination) compared to persons with a high educational level. The low prevalence of mental stimuli and challenges at work among the poorly educated subjects explained about 42% of this association. The contribution was independent of crystallized intellectual abilities and was similar across measures of cognitive function. Our findings indicate that the gap in the risk of age-related cognitive decline between the poorly and highly educated persons may be substantially narrowed by increasing work-related mental stimuli and challenges among the poorly educated subjects.