Clinical correlates of cerebral white matter hyperintensities in cognitively normal older adults.

Many research studies have demonstrated asymptomatic white matter hyperintensities (WMHs) in older adults, which are postulated to be ischemic in origin. We hypothesized that certain clinical predictors, measured in a population of healthy older adults, would have a positive relationship with WMH scoring on magnetic resonance imaging (MRI). As part of a longitudinal study of cognitive aging we have performed MRI on healthy older adults. In a group of 46 volunteers (25 females; median age 73, range 63-84 years), we have calculated of the Hachinski score and Framingham Stroke Risk Profile (FSRP). Volunteers also provided self-reported health information using the Cornell Medical Index (CMI). These were compared against the total Age Related White Matter Changes (ARWMC) score. The mean total ARWMC score was 7.4 + or - 5.27 (+ or - S.D.) and only 3 (6.5%) individuals had no evidence of WMH. Regression analysis of individual variables identified self-report of cardiovascular disease from the CMI, section C as the only significant predictor of ARWMC. A multivariate linear regression model also identified FSRP at 1 year as a second independently significant predictor. The multivariate model accounted for 19% of the variance in total ARWMC score. The only 6.5% of individuals who had no WMH is in keeping with previous studies. The important finding was the positive relationship with self-reported cardiovascular disease, which is a possible biomarker of sub-clinical cerebrovascular disease (CVD).

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.

Relationship between self-reported prevalence of diabetes mellitus using the Cornell Medical Index (CMI) and prevalence determined by glycosylated hemoglobin (HbA(1c)) in an elderly community-dwelling population.

Reports of diabetes mellitus samples in community-dwelling unselected populations suggest a prevalence of 6%. A further 3% of unknown diabetes mellitus subjects are suggested when using formal biochemical methods of diagnosis. In this study, we present the prevalence of diabetes mellitus by self-reports using the CMI and concomitant biochemical detection in 436 community-dwelling older adults who have participated in a 20-year-study of age and cognitive performance in Manchester, UK. Twenty-three of the group reported that they had diagnosed diabetes mellitus, three individuals had a raised HbA(1c) of greater than 7.0% on random testing, but no knowledge of having diabetes mellitus. These individuals were re-contacted and three said they subsequently had a diagnosis of diabetes mellitus made within the two years following the questionnaire. We conclude that in an older population of community-dwelling subjects the numbers of undiagnosed cases of diabetes mellitus is lower than anticipated, based on large unselected population samples. The greater opportunity to interact with health care professionals who may consider screening for diabetes mellitus may explain these findings.

Individual inconsistency across measures of inhibition: an investigation of the construct validity of inhibition in older adults.

Inhibition is a central construct to the frontal lobe theory of ageing, yet its construct validity remains unproven. Furthermore, age effects on measures of inhibition are often reported without adequate control for the effects of global slowing on performance. We investigated inhibitory function in older adults in two experiments. In Experiment 1, 49 people with ages between 59 and 86 (mean=70 years 9 months S.D.=7.54) completed four analogues of the Stroop interference paradigm. To control for global slowing and to enable comparisons across all measures, we used a random effects model based on log-transformed response times. Age did not contribute significantly to the model and the estimated correlation between tasks was not significant. In Experiment 2, 33 people with ages between 62 and 86 (mean=73 years 4 months, S.D.=6.57) were compared on two measures of Stroop-like interference which were very similar in surface task demands. Age did not contribute significantly to the model but the estimated correlation between tasks was robust (r=0.714). We conclude that age may make little contribution to inhibitory function independently of other factors such as speed and intelligence. Second, that the level of individual consistency in the performance of measures of inhibition will depend on the similarity of the tasks used.

Cognitive function in the Caerphilly study: associations with age social class, education and mood.

Baseline cognitive function was established for a study of pre-symptomatic cognitive decline in 1870 men from the general population aged 55-69 years as part of the third examination of the Caerphilly Study. Cognitive assessment included the AH4, a four choice serial reaction time task, a modified CAMCOG, MMSE, NART and various memory tests. Distributions and relationships with age, social class, education and mood at time of testing are presented for a younger population than has previously been available. Multiple linear regression showed cognitive function to be independently associated with all four factors. The age effect was equivalent to one half of a standard deviation (SD) in CRT and AH4 scores. Only the NART score was not associated with age, supporting the use of NART score as an estimate of pre-morbid IQ. The largest age adjusted differences between men with low and normal mood were for the AH4 (3 points, t = 5.6, p < 0.0001) and the CAMCOG (2 points, t = 5.8, p < 0.0001). The smallest age adjusted effect of mood was for the CRT (33 ms, t = 2.14, p = 0.32) and the MMSE (0.4 points, t = 2.97, p = 0.003). Age, mood and education adjusted social class effects were very large ranging between around 0.5 SD for the CRT, and 1.0 SD for the AH4 and NART, respectively. For educational status age, mood and social class adjusted differences were also substantial with tests for trend showing the largest differences for the NART (t = 12, p < 0.0001) and modified CAMCOG (t = 10.6, p < 0.0001) with the smallest differences for the CRT (t = 2.73, p = 0.006).

Contribution of cognitive abilities to performance and improvement on a substitution coding task.

Age-related performance variance on substitution coding tests has been found to account for much of the age-related variance in tests of fluid and other abilities, leading to the conclusion that cognitive decline is due to slowing. Although it is an easy task, which could easily be performed accurately given adequate time, the substitution coding task is not a pure measure of cognitive speed. Evidence from growth curve analyses involving 3,708 volunteers (49-95 years of age) from the Manchester and Newcastle Studies of Cognitive Aging (P. Rabbitt, C. Donlan, N. Bent, L. McInnes, & V. Abson, 1993) indicates that, with practice on this task, improvement is related more to memory than to age, reasoning, vocabulary, or perceptual speed. In other words, faster performances are related primarily to memory. Operational similarities between speeded measures and measures of higher order abilities, which weaken the argument for causal relationships, are discussed.

A study of performance on tests from the CANTAB battery sensitive to frontal lobe dysfunction in a large sample of normal volunteers: implications for theories of executive functioning and cognitive aging. Cambridge Neuropsychological Test Automated Battery.

Several tests from the CANTAB neuropsychological test battery previously shown to be sensitive to frontal lobe dysfunction were administered to a large group of normal volunteers (N = 341) ranging in age from 21 to 79 years. The main tests included a computerized form of the Tower of London test of planning, a self-ordered spatial working memory task, and a test of attentional set formation and shifting. A computerized form of the Corsi spatial span task was also given. Age-related graded declines in performance were seen, sometimes in a discontinuous manner, especially for the attentional set shifting task (at the extradimensional shift stage). Patterns of deficits reminiscent of frontal lobe or basal ganglia damage were observed in the oldest age group (74-79). However, overall the data were only partially consistent with the hypothesis that frontal lobe functions are the most sensitive to effects of aging. Factor analyses showed that performance in the executive tests was not simply related to a measure of fluid intelligence, and their performance had a factor loading structure distinct from that for the CANTAB tests of visual memory and learning previously administered to the same sample. Finally, only limited support was found for the hypothesis that cognitive aging depends on slowed information processing.

Uncoupling learning from initial recall: the relationship between speed and memory deficits in old age.

Nettelbeck & Rabbitt (1992) found that measures of speed of performance with low knowledge requirements (four-choice reaction time, inspection time and coding-substitution) accounted substantially for age-related changes among 104 persons aged from 54 to 85 years in a number of more complex cognitive measures reflecting general fluid ability. However, the numbers of words recalled from a list after either a single brief viewing of each word, or following a cumulative learning procedure across four trials, provided an exception to this general trend, leading to the conclusion that some aspects of memory may be independent of mental speed. A follow-up of 82 of the same people 18-20 months later was designed to partition performance in a similar cumulative learning procedure into an initial first recall component and a subsequent learning component. This was accomplished by fitting individual cumulative learning data with a hyperbolic power function which met the theoretical requirement of defining separate initial recall and learning parameters. These parameters were found to be independent and it was concluded that learning involved rehearsal, whereas first recall did not. The hyperbolic power function provided a good account for 92 per cent of individual cases. Analyses which combined Nettelbeck & Rabbitt's (1992) data with new measures confirmed the reliability of these authors' results. Furthermore, it was found that first recall, but not learning, was mediated by processing speed. Learning was relatively unaffected by age-related slowing in mental speed, suggesting that Nettelbeck & Rabbitt's results were the consequence of a strong rehearsal component in their memory tasks. Thus, while mental slowing is clearly one important aspect of cognitive decline during old age, it does not constitute a sufficient explanation for changes in all areas of cognitive functioning. Specifically, age-decline in rate of learning with rehearsal appeared to be independent of slowing in speed of information processing.

Investigating Individual Differences in a Serial Choice Reaction Time Task: Use of Auditory Feedback and Analysis of Responses Surrounding Errors.

Subjects (N = 78) performed a visual four-choice reaction time (RT) task, either with or without immediate trial-by-trial feedback, in which RT (but not accuracy) was indicated by the pitch of an auditory tone. For each feedback condition, half of the subjects (the high AH4 group) scored more than 50% on the AH4 test of fluid intelligence (Heim, 1968), whereas the remaining half (the low AH4 group) scored less than 50%. It was predicted that if low AH4 subjects were slow because they were poor at monitoring RT, they would benefit more from feedback than high AH4 subjects would. This was not supported by the data: There was some beneficial effect of feedback on RT, but only for the high AH4 group. A second possibility was that individual differences would be apparent in processes such as detecting errors and controlling RT from trial to trial. From analyses of error rates, RT distributions, and particularly sequences of responses before and after errors, there was no evidence of qualitative differences in performance between the high and low AH4 groups. It is concluded that individual differences in this task are largely determined by information-processing rate rather than by factors such as the ability to detect errors or to monitor and control RT.

Effects of age on the ability to remember common and rare proper names.

Difficulties in remembering proper nouns increase with age. One factor is that names are arbitrary labels. Another is that because many people share the same names, mutual discriminability between names is less than than that between other words. Discriminability between names may reduce as the number of acquaintances increases. Also, most people have both a first and a second name. These have to be learned as a pair, but they may be of unequal distinctiveness and so be unequally well remembered. An experiment was designed to evaluate the relative effects of distinctiveness of first and second names on free and cued recall. Subjects (aged 60-69 or 70-79 years, matched on Mill-Hill vocabulary score) were asked to remember one of four lists of 16 names. Each was presented four times. The names were either common, rare, or a combination of the two--a common first name with a rare surname, or vice versa. Subjects first freely recalled the names. They were next cued by either first name or surname to recall the remaining half of name pairs. Interactions between effects on recall of subjects' ages and of the relative distinctiveness of first and second names provide partial support for a model incorporating "relative distinctiveness" as a factor in failures of name recall in old age.

Applying Brinley plots to individuals: effects of aging on performance distributions in two speeded tasks.

This article describes the application of Brinley plots to performance distributions from 2 speeded tasks, namely, letter coding and visual search. Ss were aged either 60 years (n = 111) or 75 years (n = 111). Response times within each age group were ranked and then plotted against each other so that the best 60-year-old was paired with the best 75-year-old, and so on. For both tasks, linear fits to the functions were almost perfect, with slopes greater than 1 and with negative intercepts. Additive and multiplicative models of aging were rejected in favor of a general linear model, with different parameters for the letter coding and visual search tasks.

The problems of being an older driver: comparing the perceptions of an expert group and older drivers.

Driving instructors' observations of older drivers were compared with the experiences of older drivers themselves using two questionnaires. Instructors were asked to compare the ease or difficulty of teaching different skills to old and young pupils, and were asked what skills they would expect to have deteriorated in an experienced driver aged 70. Instructors found teaching most skills to older pupils more difficult than to younger pupils, especially vehicle control and where more than one source of information demanded attention at once. Older pupils learned skills involving attitude and safety mindedness more readily than younger ones. Accident statistics suggest that junctions are dangerous places for older drivers and specific difficulties suggested by the instructors gave clues as to why junctions should be so problematic. Some skills seem to be intrinsically difficult for older people, in that instructors suggested them for both older pupils and experienced drivers: for example, vigilance, speed and distance judgements and coordination. There were also skills that instructors noted learners found difficult that experienced older drivers did not, namely vehicle control skills, and there were problems older drivers had that older learners did not, namely complacency and poor attitude towards safety. Older drivers were unaware of many of the problems suggested by driving instructors and by previous research. Comparison of these problems (eg failures of attention) with those that the drivers were aware of (eg fatigue) suggested that part of the reason for this lack of insight may be poor feedback. This is discussed with reference to directions for remediation. Finally, the effect of greater experience on older people's insight and willingness to make sensible adjustments to their driving was examined.

Speed and accuracy of memory decisions in older adults.

An experiment examined the speed and accuracy with which older individuals made decisions about the contents of their memory. 63 volunteers aged between 50 and 80 years made speeded decisions about whether they knew the meaning of rare words presented to them on a computer screen followed by a forced-choice recognition test to assess the veracity of the memory decisions. Subjects were required to select 3 targets from a list of 10 that together constituted the definition of the original word. Analysis showed (i) the older adults were slower to decide whether or not they knew the words, (ii) positive decisions were quicker when more was known about the target, (iii) the age difference in decision speed was unrelated to the amount known about each item.

Alcohol, reaction time and memory: a meta-analysis.

Moderate doses of alcohol impair performance on a variety of information processing tasks. Two separate meta-analyses were conducted on the results of (1) reaction time studies, and (2) recognition memory studies, representing 25 and 16 different task conditions, respectively. In both cases, performance with alcohol (either 0.8 or 1.0 ml/kg body weight) was plotted as a function of performance with no alcohol. For reaction time, a linear fit accounted for 99.7 per cent of the variance. The same function applied not only to the mean but to the distribution of reaction times from the 5th to the 95th percentiles. For recognition memory, a linear fit accounted for 96.2 per cent of the variance in accuracy (expressed as the logarithm of proportion correct). Thus alcohol appears to have a general linear effect on information processing, rather than specific effects on a subset of stages. It is concluded that the results are consistent with a reduced processing resources hypothesis for the impairment with alcohol.

Effects of age-related reductions in processing resources on text recall.

Available processing resources are presumed to determine the amount of deep, elaborative processing people can carry out, with reduced resources resulting in poor integration of details from texts, but preserved selection of main points. Two experiments examined whether experimentally reducing resources and levels of processing eventually results in a failure of selection and also whether it produces in younger people the pattern of recall normally observed in elderly people. Experiment 1 examined the effect of the added demand of selecting for preferential recall of a primary theme from a two-theme text. Subjects who putatively had greater processing resources ("younger" elderly in their 60s and those with high intelligence test scores) began to behave like older and lower intelligence test score individuals in that they recalled well main points from both themes but showed reduced recall of details from the secondary theme. In a sentence recognition task, subjects in their 70s more often accepted distractor sentences that did not preserve the meaning of the original text. In Experiment 2, encouraging subjects to process text more elaborately improved recall, especially the recall of the elderly, who began to produce recall protocols resembling those of younger and higher intelligence test score individuals. However, discouraging depth of processing did not have the converse effect of reducing quality of recall by younger and high intelligence test score individuals to resemble that of the old and less able. Instead, recall was generally depressed, with recall of main points being especially affected, suggesting that the oldest, lowest ability subjects were beginning to show a failure of selection here.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of alcohol, practice, and task complexity on reaction time distributions.

The effects of alcohol (1.0 ml/kg body weight) and practice (2 sessions) were investigated in 2-, 4-, and 8-choice reaction time (RT) tasks with 24 male subjects. The number of errors increased with alcohol, practice, and increasing task complexity (choice). Mean RT decreased with practice, but increased with alcohol and complexity. Both the alcohol and practice effects on mean RT increased as complexity increased. The effects of alcohol, practice, and complexity were all larger for the higher percentiles of the RT distributions than for the lower percentiles. RT distributions were further analysed at each level of choice by plotting percentiles (5th, 10th, ... , 95th) for alcohol conditions against corresponding percentiles for no-alcohol conditions, and percentiles obtained early in practice (Session 1) against those obtained later in practice (Session 2). These plots revealed that whereas at all levels of choice the effect of alcohol could be expressed as a simple linear transformation of all RTs, the effect of practice required a more complex curvilinear transformation. Thus, alcohol produces a general slowing of all RTs, whereas practice produces a disproportionate improvement at the slower end of the RT distribution.

Ageing memory: use versus impairment.

An uncued recall technique was used to compare recall of autobiographical events by two groups of elderly volunteers of equivalent general intelligence (assessed by unadjusted scores on the AH4 intelligence test). One group lived in residential care, and the other led independent lives. Residential care subjects recalled and spontaneously rehearsed more memories from their early than their recent lives, whereas the reverse was true for the independent elderly. The effects of senile confusional states were also investigated by testing a subgroup of cognitively impaired subjects, also in residential care. Although unimpaired elderly in care produced more early than recent memories, they were still able to produce substantial numbers of recent memories. Impaired subjects produced very few memories, those they did produce were mainly early ones. Frequency of rehearsal (or reminiscence) seemed to affect the probability of elicitation of a memory. People in institutions more often rehearse memories of early events. Frequency of rehearsal is thus a function of the use which people in different situations make of their memories. Cognitive impairment due to organic neurological changes in the elderly had a characteristic effect on the abundance of recall from recent life.

Effects of alcohol and extended practice on divided-attention performance.

The effects of alcohol and extended practice on divided attention were investigated using a visual tracking task and an auditory detection task. Subjects performed the tasks with and without alcohol, under single-task (S) and dual-task (D) conditions, both before and after they had received extended practice under single-task conditions without alcohol. Tracking accuracy improved with practice and was impaired under divided-attention conditions but was not affected by alcohol. Speed of detection was impaired by alcohol, improved by practice, and impaired by divided attention. Extended practice did not reduce the influence of alcohol. The effects of both alcohol and practice on speed of detection were significantly greater under dual-task conditions than under single-task conditions. Analysis of detection-task reaction times in terms of relative divided-attention costs, (D-S)/S, showed no effect of alcohol, but a highly significant reduction in costs with extended practice. It is concluded that (1) alcohol and practice can have quantitatively, but not qualitatively, similar effects on speeded performance, and (2) the effect of alcohol is not influenced by the attentional requirements of the task.

Autobiographical and text recall in the elderly: an investigation of a processing resource deficit.

This study examined different explanations of age-related impairments in recall of details from text and autobiographical events. An interpretation of Central Executive Capacity Deficit was supported and explored further. This suggests that details are more demanding of capacity than main points, and that ability to appropriately integrate details with context is likely to be impaired. An implication was that irrelevant and false information may occur, and this was supported in both autobiographical and text recall. The effects were then examined in relation to various measures of ability. The aim was to determine whether declining capacity (as indicated by "Fluid Intelligence" measures) predicted ability to recall in a detailed manner. The difficulty with details was predicted independently by chronological age and by measures of fluid (e.g. AH4 intelligence test) and the more crystallized verbal ability (Mill Hill vocabulary test). Only a measure of the specificity of autobiographical recall was predicted solely by measures of fluid intelligence. Decreased specificity was not a result of faster decay of memory for details, as there was little difference across the lifespan. The resource deficit appears to affect retrieval and appropriate implementation of detail. It was concluded that lower-ability elderly subjects have decreased Central Executive resources, which leads to poor (often inappropriate) integration of details with central thematic points, but that subjects' verbal ability, which does not decline with age, still has an important part to play.

Comparing the effects of alcohol and intelligence on text recall and recognition.

Forty male subjects were divided into two groups on the basis of their scores on a computerized intelligence test administered in a preliminary session. They then participated in a text recall and recognition experiment in which they received alcohol (1.0 ml/kg body weight) in one session and no alcohol in another session (the order being counterbalanced). Subjects were required to read a short passage, immediately recall as much of it as possible and then select from sets of four sentences the ones that appeared in the original passage (recognition). Although two different passages were used, and subjects knew about the memory tasks in advance, there was nevertheless a significant practice effect: subjects recalled 10.6 per cent more propositions on the second occasion than on the first, but this could be at least partly explained by the fact that they spent 10.0 per cent longer reading the second passage. There was also a significant 7.8 per cent slowing of reading time due to alcohol. Practice did not interact with either intelligence or alcohol on any measure of performance. Alcohol impaired the performance of high intelligence test scorers more than low scorers. The effects of intelligence and alcohol on free recall were quantitatively similar: high intelligence test scorers recalled 8.7 more propositions than low scorers; with alcohol, subjects recalled 8.3 fewer propositions than without alcohol. However, the effects were qualitatively different. The effect of intelligence was primarily on the recall of lower level propositions, whereas alcohol impaired the recall of both higher and lower level propositions. Furthermore, while there was no effect of intelligence on recognition, alcohol impaired performance such that more incorrect sentences were erroneously recognized, particularly those which altered the meaning of the original sentence, rather than merely its surface structure. In terms of Kintsch & van Dijk's (1978) model of text processing, the results are interpreted as suggesting that, while both intelligence and alcohol affect the capacity of the short-term memory buffer, there is an additional impairment with alcohol in the ability to select between higher and lower level propositions prior to filling the buffer.