Lesley Stewart

The Executive Decline Hypothesis of Cognitive Aging: Do Executive Deficits Qualify as Differential Deficits and Do They Mediate Age-Related Memory Decline?*

This paper reports the results of two studies which investigated whether aging is associated with a differential deficit in executive function, compared with deficits in general cognitive ability (Wechsler Adult Intelligence Scale-Revised performance). Further, the studies investigated the specificity of the executive decline hypothesis of memory and aging by examining whether declines in executive function mediate age-related memory decline over and above the variance in memory accounted for by general cognitive ability. The results of Study 1 showed no consistent evidence of a differential decline in executive function among a sample of participants aged between 18 and 75 years. The results of Study 2 indicated a differential decline in one indicator of executive function, the Modified Card Sorting Test, among an older sample aged between 60 and 89 years. Both studies demonstrated that measures of executive function accounted for age-related variance in free recall, recognition, and serial recall, even after controlling for general cognitive ability. However, in Study 1, once variance attributed to speed of processing was taken into account, executive function did not contribute further to the age-related variance.

Demonstration of savings on the AVLT and development of a parallel form.

The purposes of the present study were (1) to investigate whether significant savings occur with repeat testing on Reys Auditory-Verbal Learning Test and (2) to develop a parallel version of the AVLT. Subjects (N = 60) were divided into pairs (individually matched for sex, age, and education) to form two groups and were administered either the AVLT or a parallel version. Results indicated no significant differences on all AVLT measures of learning, recall, and recognition, suggesting that the parallel version can be used as an equivalent form of the AVLT. Subjects were retested after an interval of 27 (+/- 3) days, with half receiving the same version and half receiving a different version. In contrast to subjects receiving different lists, those who were retested with the same version demonstrated a significant improvement in performance on the majority of AVLT variables.

Clinical features predicting dementia in idiopathic Parkinson's disease A follow‐up study

We followed up, after 31/2 years, a whole population cohort of 249 patients with Parkinsons disease (PD) 1st examined in 1983 to 1984. Of the survivors, 23.6% qualified for a DSM III-R diagnosis of dementia. In univariate tests, age, certain items of the Webster scale, the Hoehn and Yahr scale, a 10-question mental status questionnaire, and a history of smoking were associated with a diagnosis of dementia 31/2 years later. Logistic regression with DSM III-R diagnosis (demented versus nondemented) as the dependent variable, and age and symptom scales for PD as predictor variables, revealed that PD symptoms predicted dementia even after controlling for age. We conclude that dementia is probably more common in PD patients than would be expected in the general population and is associated with the severity of PD symptoms and signs independently of age.

Construct validity of the National Adult Reading Test: a factor analytic study

Abstract Factor analysis was carried out on the National Adult Reading Test (NART) and Wechsler Adult Intelligence Scale (WAIS) performance of 139 normal subjects. The NART loaded very highly on factor I extracted by principal components analysis (PCA), suggesting that the NART has high construct validity as a measure of general intelligence. Varimax rotation of the three factors extracted by PCA produced a factor structure that was consistent with previous factor analytic studies of the WAIS. The NART loaded highly on Factor I (verbal intelligence) but not on Factor II (non-verbal intelligence) or Factor III (attention/concentration).

Estimation of premorbid intelligence: combining psychometric and demographic approaches improves predictive accuracy

Abstract Regression equations have been developed to estimate premorbid WAIS IQ from (a) psychometric tests which are relatively resistant to the effects of cerebral dysfunction, and (b) demographic variables (e.g. education, occupation). The purpose of the present study was to determine whether regression equations based on the combination of psychometric and demographic variables would account for more WAIS IQ variance than either of the two methods alone. Normal subjects (n = 151) were administered the WAIS and the National Adult Reading Test and had their demographic details recorded (age, sex, education, and occupation). Equations incorporating the NART and demographic variables accounted for 73, 78 and 39% of the variance in Full Scale, Verbal, and Performance IQ. The corresponding figures for equations derived from the NART alone or demographics alone were 66, 72 and 33%, and 50, 50, and 30% respectively.

Event related potentials, reaction time, and cognitive performance in idiopathic Parkinson's disease

Sixteen non-demented patients with idiopathic Parkinsons disease (PD) with varying degrees of cognitive impairment and sixteen age-, sex- and education-matched normal controls were examined with (1) an auditory oddball paradigm requiring counting or a motor response in separate determinations, (2) a reaction time task with movement time component and (3) a detailed clinical and neuropsychological test battery. Patients were impaired on a number of neuropsychological tests. They also showed an increased P2 and N2 latency, but no significant increase in P3 latency. Their response initiation times and reaction times during the oddball experiment were not different from controls, whereas movement time was significantly increased. Increased peak latencies, particularly for N2, were moderately associated with Parkinsonian motor impairment in patients and with the Benton Multiple Choice Visual Retention Test in patients and controls. Movement time was associated with P3 latency only in controls and in both groups with the Benton Multiple Choice Visual Retention Test. The observed pattern of results suggests that in non-demented PD patients ERP peak latencies, visuo-spatial task performance and Parkinsonian motor impairment share a significant degree of variance. While impairments in neuropsychological tests and delay in the earlier peaks P2 and N2 do not appear to be sensitive to medication with L-DOPA, normal P3 latencies might indicate good pharmacological symptom control in the absence of dementia.

Mortality and causes of death in idiopathic Parkinson's disease: results from the Aberdeen whole population study.

Two hundred and forty-nine patients with Parkinsons disease previously examined by Mutch et al 1,2 were followed up three and a half years after the original study. Cognitive impairment, age, some postural signs and symptoms of Parkinsons disease and high scores on the Hoehn and Yahr scale predicted premature death. Patients were more likely to die from respiratory infections than controls. Respiratory diseases as cause of death recorded on the death certificate were not related to kyphosis, posture scores or Hoehn and Yahr scores before death. The hypothesis is advanced that death of respiratory causes might be associated with signs of general autonomic dysregulation.

DEMENTIA IN IDIOPATHIC PARKINSON'S DISEASE : PREVALENCE AND RELATIONSHIP WITH SYMPTOMS AND SIGNS OF PARKINSONISM

A whole population cohort of 157 patients with idiopathic Parkinsonism, most of whom had previously been clinically examined by Mutch (1986a), were assessed to determine prevalence figures for dementia and examine the relationship between dementia, cognitive impairment and Parkinsonian signs. Dementia according to DSM-III-R criteria was diagnosed in 23.3% of all patients (95% confidence interval: 17.1 to 32.4%). Dementia and cognitive impairment were associated with overall measures of Parkinsonian impairment and rigidity, but not tremor, even after controlling for age, sex and education.

Does idiopathic parkinsonism in Aberdeen follow intrauterine influenza

A study is presented which fails to replicate a recent report that peak years of birth of patients later developing Parkinsons disease are related to the influenza pandemics of the period 1890-1930. The years of birth of a whole population cohort of 243 patients suffering from Parkinsons disease examined in Aberdeen in 1983 and reexamined in 1986/7 were compared with deaths due to influenza in the City of Aberdeen in the years 1900-1930. Although a significant peak of Parkinson births (compared with the age profile of the Aberdeen population in 1983) occurred in 1902, there appeared to be no systematic relationship between Parkinson births and influenza deaths. In addition, no season of birth effect could be detected in a comparison with 232 matched controls. The presence of peaks of birth years, for whatever aetiological reason, is of significance to epidemiological studies in that prevalence estimates may be influenced by the year of study relative to these mini-cohorts.

Premorbid IQ estimates obtained by combining the NART and demographic variables: Construct validity

Abstract Crowford, Stewart, Parker, Besson & Cochrane ( Personality and Individual Differences , 10 , 793–796, 1989a) have recently built regression equations to estimate premorbid IQ from the National Adult Reading Test (Nelson, 1982) and demographic variables. The construct validity of this IQ estimate was examined in a sample of 151 non-clinical subjects. Factor analysis was performed on WAIS subtests and the NART/demographic estimate (NDE). The loadings of these variables on the first unrotated principal component (which represents g or general intelligence) was examined. The g loading of the NDE was 0.90, which was higher than any of the WAIS subtests. This result suggests that the NDE has very high construct validity and is superior to the NART alone as a measure of premorbid g .