Cognition in Healthy Aging

The study of cognitive change across a life span, both in pathological and healthy samples, has been heavily influenced by developments in cognitive psychology as a theoretical paradigm, neuropsychology and other bio-medical fields; this alongside the increase in new longitudinal and cohort designs, complemented in the last decades by the evaluation of experimental interventions. Here, a review of aging databases was conducted, looking for the most relevant studies carried out on cognitive functioning in healthy older adults. The aim was to review not only longitudinal, cross-sectional or cohort studies, but also by intervention program evaluations. The most important studies, searching for long-term patterns of stability and change of cognitive measures across a life span and in old age, have shown a great range of inter-individual variability in cognitive functioning changes attributed to age. Furthermore, intellectual functioning in healthy individuals seems to decline rather late in life, if ever, as shown in longitudinal studies where age-related decline of cognitive functioning occurs later in life than indicated by cross-sectional studies. The longitudinal evidence and experimental trials have shown the benefits of aerobic physical exercise and an intellectually engaged lifestyle, suggesting that bio-psycho-socioenvironmental factors concurrently with age predict or determine both positive or negative change or stability in cognition in later life.

The results indicated that the majority of age-related differences appear to be shared across different cognitive variables and are well predicted by individual differences in higher order factors The independent age-related effects, after considering the relations of age to what all variables had in common, were small relative to the total age-related effects. Finkel et al (1998) N=85 individuals aged 41-84 at first assessment. From the Swedish Adoption/Twin Study of Aging Longitudinal: 3 times of measurement separated by 3-year intervals Verbal ability, spatial abilities, Memory tests, perceptual speed Stable mean performance in the younger cohorts and longitudinal decreases in mean performance in the older cohorts. Cross-sectional comparisons were more likely to indicate that older cohorts have equal or less variability than younger cohorts. Heritability of the general cognitive ability factor showed significant longitudinal decreases over time in the older cohorts.
Significantly higher negative age correlations for the 3 mechanic abilities (perceptual speed; memory; reasoning) than the 2 pragmatic abilities (knowledge; fluency) up to the age of 70. The differences between the 2 dimensions of intelligence appear to decrease with increasing age Linderberger y Reischies (1999).
N= 516 persons aged 70-103. Cross-sectional The BASE cognitive test battery. In this report they focused on 3 measures: 1) Enhanced Cued recall test, to estimate interindividual differences in encoding specificity.
2) The MMSE and 3) an index of brain atrophy base don a CT scan of the brain The distinction between fluid and crystallized intelectual abilities extends into old and very old age, but compared with earlier periods of the life-span, this distintion appears to be less pronounced. About a third of the interindividual variability was related to chronological age; the highest relationship was found for perceptual speed (38% if the reliable variance).
Caskie, Schaie y Willis (1999). N=1.745 participants from 11 cohorts of the Seattle Longitudinal Study (SLS). Aged 25 to 81 cohort-sequential study design The Verbal Meaning, Spatial Orientation, and Reasoning sub-tests from the Thurstone Primary Mental Abilities Test Verbal, spatial, and reasoning ability raw scores were re-scaled to a T-score metric to allow all abilities to be compared on the same measurement scale Rate of decline over time in all abilities was related to level of ability at age 67, the age at which decline tends to begin. Cohort, gender, and level of education explained individual variation in the rate of decline for spatial ability. The rate of decline in verbal ability was predicted by cohort, and rate of decline in reasoning ability was predicted by both cohort and education Being in a later birth cohort and having a higher level of education were both associated with higher levels of ability at age 67. Women had significantly higher levels of verbal and reasoning ability at age 67 than men, but men had significantly higher spatial ability at age 67 than women. Eleven tests that represent crystallized knowledge and five abilities associated with fluid abilities, and speed.

Study
In crystallized knowledge and episodic memory, individuals with a shorter survival (deceased between T2 and T3) showed a steeper decline compared with those who survived longer. Level of cognitive performance in late life is associated with proximity to death, that this relationship is longstanding, and that it is partially influenced by compromised cardio-and cerebrovascular functioning. Deborah Finkel & Nancy L. Pedersen (2004) Q1 (1984) In-person testing (IPT) involved an interview, administration of cognitive tests and a health examination of a subset of the SATSA twins. The cognitive battery was designed to represent the domains of crystallized and fluid intelligence, and memory. Additional measures of spatial ability and perceptual speed Stability or even improvement for measures of crystallized ability up to age 70, followed by significant decline. Cognitives tasks with a large speed component show a significant acceleration in linear decline after age 65. Declines in heritability in late adulthood with associated increases in environmental variance. The genetic variance in cognitive functioning in the middle-aged cohort was defined primarily by motor speed, whereas genetic variance in the older cohort was defined by perceptual speed. Observed decline in many community dwelling older people is likely to be a function of disuse and is therefore reversible for many. Training effects are long-lasting with the trained participants still at an advantage over their controls after 7 and 14 years Li, S.-C., Lindenberger, U., Hommel, B., Aschersleben, G. Maximum processing speed, processing robustness, and fluid intelligence were achieved by individuals in their mid 20s. Decrements were already visible by the mid 30s While the maximum crystallized intelligence scores were achieved by individuals in their 40s, and crystallized intelligence scores remained relatively stable until old age, at which point they also declined (beyond 70 years of age). A larger percentage of the predicted variance in chronological age was jointly shared between processing speed and the two facets of intelligence, amounting to 69% of the explained variance in old age. Tucker-rob y Salthouse (2008 Prospective cohort study. After baseline, interviews were conducted on all the survivors an average of 2, 7 and 9 years later.

MMSE
Higher educational level and social class, better mobility and younger age at baseline were identified as statistically significant positive factors for cognitive performance. Women and participants with better mobility were found to experience a slower decline with age than men and participants with poorer mobility. Higher levels of education do not appear to protect against cognitive decline, though if the MMSE is used in the diagnostic process, individuals with less education may be diagnosed as having dementia somewhat earlier Brown, MT (2010).
N=16.513 subjects and 53,900 observations. Aged 65+ From the Asset and Health Dynamics among the Oldest-Old study (AHEAD) and the HRS.

Longitudinal
Modified version of the TICS instrument. A combined history of childhood disadvantage and psychiatric problems more strongly affects cognitive function, but cognitive declines remain consistent with those associated with psychiatric history. These effects are partially mediated by later-life demographic, socioeconomic, or health characteristics. Within-cohort differences across ages were often as large as between-cohort differences across ages.
The ACTIVE study's cognitive battery was comprised mostly of age-sensitive measures of information processing and fluid intelligence (Horn & Cattell, 1967;Baltes et al., 1980). Four areas of cognitive ability were assessed within the battery. Inductive reasoning, Episodic Modeling revealed an overall inverted-U shape (quadratic) trajectory across cognitive domains. Level and slope in reasoning demonstrated the closest association to level and slope of everyday cognition, and accounted for most of the individual differences in linear gain in everyday cognition. There was a sex difference in the cognitive-decline trajectories for verbal and visuospatial task performance after the 50s. Women showed better performance than men in the age group of 60s, while men showed better performance than women in the age group of 80s. For women, performance of both verbal and spatial tasks declines gradually as age increase, but remain stable from 50s to 60s and then declines linearly from 60s to 80s. For men, performance of both verbal and spatial tasks declines gradually as age increases and there was no turning point of prominent cognitive decline. Downer et al (2016)

MMSE
Nearly 31% of the final sample maintained high global cognition (persistent high), 52.6% experienced slight decline (decline but high), and 15% experienced severe decline in global cognition (decline to low). Advancing age, requiring help with one or more ADLs, and high depressive symptoms were all significantly associated with being in the decline to low trajectory class, whereas greater educational attainment was significantly associated with increased likelihood in the decline but high and persistent high trajectory classes. Participants who were not married and lived alone were 2.16 times as likely as those who were married and living with another person to be in the decline but high trajectory class. Salthouse (2016).
cross-sectional N=5,014) longitudinal N =1,353, a subset from the cross-sectional sample Aged: 18-99y cross-sectional and 3occasion longitudinal Reasoning. Spatial visualization. Vocabulary. Verbal memory. Perceptual Adult age appears to have weak relations with specific measures of cognitive functioning, defined as independent of influences shared across different types of cognitive measures, and that this is true in both crosssectional and longitudinal comparisons. The longitudinal age relations differed from the cross-sectional relations in exhibiting increases rather than decreases in the average score among adults younger than about 50 years of age. Salhouse (2017). N= 2.546 adults Aged: 18-95y Longitudinal: 2 ocassions Reasoning. Spatial visualization. Vocabulary. Verbal memory. Perceptual speed Although increased age was associated with specific influences on speed in crosssectional comparisons, and in memory change in longitudinal comparisons among older adults, most of the relations between age and cognitive functioning in both crosssectional and longitudinal comparisons were manifested as general influences shared with other cognitive measures.