Cerebral white matter abnormalities and lifetime cognitive change: a 67-year follow-up of the Scottish Mental Survey of 1932

What's behind the decline? The role of white matter in brain aging

The specific molecular events that underlie the age-related loss of cognitive function are poorly understood. Although not experimentally substantiated, age-dependent neuronal loss has long been considered central to age-related cognitive decline. More recently, age-related changes in brain white matter have taken precedence in explaining the steady decline in cognitive domains seen in non-diseased elderly. Characteristic alterations in the ultrastructure of myelin coupled with evidence of inflammatory processes present in the white matter of several different species suggest that specific molecular events within brain white matter may better explain observed pathological changes and cognitive deficits. This review focuses on recent evidence highlighting the importance of white matter in deciphering the course of "normal" brain aging.

Smoking and cognitive change from age 11 to 66 years: a confirmatory investigation

Previously we reported that smoking is associated with a small relative decline in cognition from childhood to old age. In this study we perform confirmatory analyses on a further wave of data collected from 298 of the participants, all with age 11 IQ scores, at age 66years, 2years after the original observations. Non-smokers scored a mean 4.9 memory test and 2.6 information processing speed test points and ex-smokers 3.5 memory test and 1.9 information processing speed test points higher than current smokers respectively over the two waves of testing, equivalent to 4-8% of mean test scores, adjusted for the effects of childhood IQ. Across tests a 100l/min higher Peak Expiratory Flow Rate was associated with a 3-4% higher test score at ages 64 and 66years. These data confirm the adverse effect of smoking on information processing speed, and provide new evidence for a similar adverse effect on memory for people in their mid-sixties.

Management of elder sexual abuse cases in critical care settings

Elder sexual abuse remains a silent and often invisible crime in persons who have limited cognitive abilities. On occasion, physical injury to elders is serious enough to require hospitalization and at that point, critical care nurses swing into action. In addition to providing acute care interventions, nurses can collect important forensic evidence through documenting and photographing injuries and reporting suspected cases to proper authorities.

The relation of white matter hyperintensities to cognitive performance in the normal old: education matters

This study examined whether the severity of cerebral white matter abnormalities (evident on MR images as white matter hyperintensities (WMH)) was related to the cognitive performance of 141 high-functioning older adults. The elderly showed the typical age decrement on measures of processing speed, working memory, and inhibition; however WMH severity was significantly related only to processing speed. The strength of this relationship was, however, influenced by the educational level of the participants, such that processing speed was more associated with WMH severity in less-educated than in well-educated participants. This is consistent with recent concepts of cognitive reserve, but does raise a question as to the underlying source of the cognitive decrement found in the sort of well-educated elders typically used in cognitive-aging studies.

The association of lead exposure and motor performance mediated by cerebral white matter change

The goals were to determine if lead exposure is associated with cerebral white matter changes (WMC) and if so, does WMC mediate the relation between lead and psychomotor slowing as measured by Grooved Pegboard (GP). In the literature, age is the strongest predictor of WMC and therefore 61 lead smelter workers age 50 and under were included in the study population. Mean (range) age was 40 (23-50) years, years of education was 9 (0-13), duration of employment was 19 (1-26), current blood lead (PbB) was 29 (16-42) microg/dl, working lifetime weighted integrated blood lead (IBL) was 826 (65-1451) microg year/dl, working lifetime weighted average blood lead (TWA) was 42 (17-59) microg/dl, and bone lead (PbBn) was 39 (-12-90) microg Pb/g bone mineral. WMC, recorded as hyperintensities on T2-weighted MRI of the brain were graded. Lead variables were entered in a logistic regression attempting to differentiate normal versus abnormal MRI, after controlling for age and cerebrovascular risk factors. Direct effects of lead on GP and indirect effects of lead on GP through WMC was modeled using multiple linear regression analyses after controlling for the covariates. WMC were present in 23% of MRIs. Logistic regression of WMC on lead exposure metrics demonstrated significantly elevated odds ratios for IBL, TWA, and PbBn after the covariates. Of the lead exposure variables, IBL (beta=0.339, p<0.10) had a larger direct effect on GP after adjusting for the covariates than PbBn (beta=0.265, p<0.10). After adjusting for the lead term and covariates WMC accounted for an additional effect on GP performance after PbBn (beta=0.261, p<0.10) and after IBL (beta=0.278, p<0.05). Path analysis demonstrated that some of the relationship of both PbBn and IBL with GP is mediated by WMC.

Balance marks cognitive changes in old age because it reflects global brain atrophy and cerebro-arterial blood-flow

In healthy old age biomarkers such as Balance robustly correlate with measures of mental abilities such as scores on tests of intelligence, reaction times and memory. A plausible explanation is that balance reflects general physiological fitness and so also neurophysiological integrity, but direct evidence is lacking. Brain scans measured age-associated loss of brain volume and cerebro-arterial blood flow (CBf) in 69 volunteers aged from 62 to 81 years who also took the Tinetti Balance test battery, 3 tests of fluid intelligence, 3 tests of decision speed and a memory test. Balance, but not atrophy or CBf, predicted intelligence test scores. Balance, atrophy, and CBf all independently predicted speed and memory scores but, after variance in atrophy and CBf had been considered, predictions from Balance were no longer significant. It appears that in these tests Balance marks cognitive performance in old age because it reflects gross age-related neurophysiological changes.

Cognitive correlates of cerebral white matter lesions and water diffusion tensor parameters in community-dwelling older people

BACKGROUND

The biological basis of cognitive ageing is unknown. One underlying process might be disruption of white matter tracts connecting cortical regions. White matter lesions (WML) seen on structural MRI may disrupt cortical connections, but diffusion tensor MRI (DT-MRI) parameters - mean diffusivity (<D>) and fractional anisotropy (FA) - may reflect more subtle changes in white matter integrity. Here the relationships between WML load, DT-MRI parameters and cognition in a large cohort of elderly subjects with a very narrow age range were investigated.

METHODS

105 community-dwelling volunteers underwent MRI and neuropsychological assessment. Seventy-two (68.6%) were female, and their mean age was 78.4 (SD 1.5) years. Scans were rated for WML load. <D> and FA were measured from regions of interest in normal-appearing frontal and occipital white matter, and centrum semiovale.

RESULTS

<D> and FA differed significantly among the three brain regions studied (p << 0.01). <D> increased with age (r = 0.22 to 0.35, p < 0.03), and was negatively correlated with FA (r = -0.20 to -0.51, p < 0.05) in all three regions. There was a trend towards increased WML load correlating with poorer cognitive function, and this was statistically significant for the Mini-Mental State Examination (rho = -0.23, p = 0.02). <D> was generally negatively correlated with cognitive test score, and FA was positively correlated. This pattern was more consistent for <D> than for FA, and particularly for verbal fluency (<D>: r = -0.22 to -0.27, p < 0.03), which measures executive function.

CONCLUSIONS

DT-MRI parameters, in particular <D>, are sensitive to early ultrastructural changes underlying cognitive ageing. Executive function may be the cognitive domain most sensitive to age-related decline in white matter tract integrity.

Brain white matter hyperintensities: relative importance of vascular risk factors in nondemented elderly people

PURPOSE

To prospectively determine whether there is an association between brain white matter signal hyperintensities on magnetic resonance (MR) images and potential risk factors for cerebral ischemia in a well-characterized narrow age cohort of nondemented community-dwelling elderly people.

MATERIALS AND METHODS

The study population consisted of surviving members of the Aberdeen 1921 Birth Cohort, a subsample of participants in the 1932 Scottish Mental Survey who were born in 1921. With the permission of the local ethics committee and with informed written consent, 106 nondemented subjects (62 men, 44 women) aged 78-79 years underwent T2-weighted brain MR imaging. Brain MR images were scored semiquantitatively for deep white matter hyperintensities and periventricular hyperintensities. Vascular risk factors and clinical measures potentially associated with cerebral ischemia included hypertension, diabetes, cerebrovascular disease, smoking, body mass index grade, respiratory function levels (forced expiratory volume in 1 second [FEV1], forced vital capacity [FVC], and peak expiratory flow rate [PEFR]) normalized for subject's height, plasma lipid levels (cholesterol, triglycerides, high-density lipoprotein, and low-density lipoprotein), glycated hemoglobin level, and mean fasting blood glucose level. Pearson correlation coefficients were calculated for correlations between potential vascular risk factors and scores for deep white matter and periventricular hyperintensities, and stepwise multiple linear regression analysis was performed for factors with a statistically significant correlation.

RESULTS

Significant Pearson correlations with deep white matter hyperintensities were found for glycated hemoglobin level (r = 0.31), hypertension (r = 0.27), normalized FEV1 (r = -0.27), normalized FVC (r = -0.22), normalized PEFR (r = -0.27), low-density lipoprotein (r = 0.24), and cholesterol (r = 0.20), and with periventricular hyperintensities for glycated hemoglobin level (r = 0.28) and normalized PEFR (r = -0.23). Multiple linear regression analysis showed that glycated hemoglobin level and hypertension were predictive of 16.2% of the variance in deep white matter hyperintensities. When subjects with non-insulin-dependent (type 2) diabetes mellitus (n = 11) were excluded, hypertension and decreased normalized PEFR were predictive of 11.7% of the variance.

CONCLUSION

White matter hyperintensities are associated with elevated levels of glycated hemoglobin in nondemented community-dwelling elderly subjects. Hypertension and decreased normalized PEFR are the principal predictors of deep white matter hyperintensities in nondiabetic subjects.

Relationship of Leukoaraiosis to Cognitive Decline and Cognitive Aging

OBJECTIVE

Leukoaraiosis (LA) is a common finding on MRI scans of the elderly. However, its exact relationship to cognitive decline and dementia is in dispute. Because LA involves the paracallosal white matter, we sought to determine if LA, uncomplicated by ischemic lesions or complaints of cognitive impairment, is associated with cognitive loss or difficulties with interhemispheric integration of behavioral functions.

METHODS

Two hundred fifty-seven MRI scans with deep white matter changes were screened. After a chart review, 38 patients had uncomplicated LA, and 31 gave informed consent to undergo cognitive and behavioral testing.

RESULTS

LA severity was not related to any of the cognitive or behavioral assessments. However, some dependent measures showed medium effect sizes that were in keeping with published findings, indicating that LA has a marginal impact on cognition. In comparison, robust relationships with age were found for certain tasks, suggesting that our cohort size was sufficient to detect meaningful clinical relationships.

CONCLUSION

Based on statistical interpretations using effect sizes, LA severity may be better viewed as a biomarker for physiological brain aging that is in advance of chronological age, leaving the elderly individual at greater risk for developing dementia.

Enlarged perivascular spaces are associated with cognitive function in healthy elderly men

OBJECTIVES

Increased white matter (WM) lesions on magnetic resonance imaging (MRI) are associated with worse cognitive function in older people. Enlarged perivascular spaces (EPVS) commonly coexist with and share some risk factors for WM lesions but are not quantified in published scales. It is not known whether the extent of EPVS is also associated with cognitive function. We tested the hypothesis that more EPVS would be associated with worse cognitive function.

METHODS

Ninety seven healthy men (65-70 years), not on medications, underwent MRI scanning and comprehensive cognitive testing. EPVS were quantified in both the basal ganglia/centrum semiovale and the hippocampus, and WM lesions were measured.

RESULTS

Scores on published WM lesion rating scales intercorrelated highly significantly and positively (rho = 0.61 to 0.91, p<0.0001). A summary (WML) factor derived from principal components analysis of the WM scales correlated with EPVS in the basal ganglia/centrum semiovale (rho = 0.48, p<0.0001) but not in the hippocampus. EPVS scores in the basal ganglia/centrum semiovale correlated significantly and negatively with non-verbal reasoning (rho = -0.21, p = 0.038) and general visuospatial ability (rho = -0.22, p = 0.032), adjusted for prior intelligence. The WML factor correlated significantly and negatively with visuospatial ability, as previously reported, and showed an unexpected positive correlation with one test of verbal memory (list-learning).

CONCLUSIONS

These findings suggest that increased EPVS are correlated with worse cognitive function. Future studies examining changes in WM with ageing should consider incorporating measures of EPVS and examine the sequence of EPVS and WM lesion development over time. More work is needed to develop valid and reliable measures of EPVS.

Introduction to the special section on cognitive abilities: 100 years after Spearman's (1904) "'General intelligence,' objectively determined and measured"

The study of individual differences in cognitive abilities is one of the few branches of psychological science to amass a coherent body of empirical knowledge withstanding the test of time. There is wide consensus that cognitive abilities are organized hierarchically, and C. Spearman's (1904) general intelligence occupies the vertex of this hierarchy. In addition, specific abilities beyond general intelligence refine longitudinal forecasts of important social phenomena and paint a rich portrait of this important domain of psychological diversity. This opening article identifies and then reviews 5 major areas concerning the personological significance of cognitive abilities and the methods used to study them. In models of human behavior and important life outcomes, cognitive abilities are critical in more ways than social scientists realize.

What provides cerebral reserve?

The cerebral reserve hypothesis is a heuristic concept used to explain apparent protection from the onset of cerebral disease and/or cognitive decline in old age. A significant obstacle when investigating the reserve hypothesis is the absence of baseline data with which to compare current cognitive status. We tested the influence of three hypothesized proxies of reserve (education, head size and occupational attainment [OCC]) in 92 volunteers born in 1921, whose cognitive function was measured at age 11 and 79 years, and who underwent brain MRI. The association between each proxy and old age cognitive function was tested, adjusting for variance contributed by childhood mental ability and detrimental age-related pathological changes measured using MRI. The results showed that education and OCC, but not total intracranial volume (TICV), contribute to cerebral reserve and help retain cognitive function in old age. Education was found to contribute between 5 and 6% of the variance found in old age memory function but was found to have no significant association with reasoning abilities. OCC was found to contribute around 5% of the variance found in old age memory function and between 6 and 8% of the variance found in old age reasoning abilities. We conclude that the intellectual challenges experienced during life, such as education and occupation, accumulate reserve and allow cognitive function to be maintained in old age.

Relationship between hippocampal volume and memory ability in healthy individuals across the lifespan: review and meta-analysis

Poor memory ability and small hippocampal volume measurements in magnetic resonance images co-occur in neurological patients. Numerous studies have examined the relationship between memory performance and hippocampal volumes in participants without neurological or psychiatric disorders, with widely varying results. Three hypotheses about volume-memory relationships in the normal human brain are discussed: "bigger is always better", a neuropsychological view that volume decreases due to normal aging are accompanied by memory decline, and a developmental perspective that regressive events in development may result in negative correlations between hippocampal volume and memory ability. Meta-analysis of results from 33 studies led to little support for the bigger-is-better hypothesis. A negative relationship between hippocampal volume and memory (smaller is better) was significant for studies with children, adolescents, and young adults. For studies with older adults, the most striking observation was extreme variability: the evidence for a positive relationship between hippocampal size and episodic memory ability in older adults was surprisingly weak. Some of the variability in results from older adults was associated with statistical methods of normalizing for age and head size, which are discussed.

The Impact of Childhood Intelligence on Later Life: Following Up the Scottish Mental Surveys of 1932 and 1947

The Scottish Mental Surveys of 1932 and 1947 collected valid IQ-type test scores for almost everyone born in 1921 and 1936 and attending school on June 1, 1932 (N=89,498) and June 4, 1947 (N=70,805). These surveys are described. This research, using the surveys' data, examined (a) the stability of intelligence differences across the life span, (b) the determinants of cognitive change from childhood to old age, and (c) the impact of childhood intelligence on survival and health in old age. Surviving participants of the Scottish Mental Surveys were tested, and the surveys' data were linked with public and health records. Novel findings on the stability of IQ scores from age 11 to age 80; sex differences in cognitive aging; the dedifferentiation hypothesis of cognitive aging; and the effect of childhood IQ on all-cause and specific mortality, morbidity, and frailty in old age are presented.