Christine Lowe

White matter lesions account for all age-related declines in speed but not in intelligence.

MRI scans measured white matter lesion prevalence (WMLP) in 65 people ages 65-84 years who also took 17 cognitive tests: 3 tests of general fluid intelligence, 3 of vocabulary, 2 of episodic and 3 of working memory, 2 of processing speed, and 4 of frontal and executive function. Entry of age with WMLP into regression equations as predictors of test scores showed that inferences about the functional relationships between markers of brain aging and cognitive impairments are seriously misleading if they are based on simple correlations alone. A new finding that WMLP accounts for all of the age-related variance between individuals in tests of speed and executive ability but for none of the age-related variance in intelligence revises current hypotheses that gross brain changes affect general fluid intelligence and other mental abilities solely through their effects on information-processing speed.

Frontal tests and models for cognitive ageing

Results of investigations of how specific behavioural changes in old age may be related to local changes in the brain have been discrepant because of neglect of methodological issues. Among these are neglect of the reliability and validity of frontal and executive tests; the operational definition and construct validity of hypothetical functional processes such as “inhibition”; the nature and origins of mutual relationships between tests; the relationships of test performance to higher order constructs of general mental ability such as “gf” and, most importantly, problems of cohort selection arising from imprecise definitions of the models of the ageing process. These problems are illustrated by a discussion of the results of several experiments in which younger and older groups of people are compared on frontal and executive tests.

Vision and touch in ageing: crossmodal selective attention and visuotactile spatial interactions.

We investigated whether ageing affects crossmodal selective attention (the ability to focus on a relevant sensory modality and ignore an irrelevant modality) and the spatial constraints on such selective processing. Three groups of 24 participants were tested: Young (19-25 years), Young-Old (65-72 years) and Old-Old (76-92 years). The participants had to judge the elevation of vibrotactile targets (upper/index finger and lower/thumb), presented randomly to either hand while ignoring concurrent visual distractors. In a second task, the role of the target and distractor modalities was reversed. Crossmodal selective attention was assessed by comparing performance in the presence versus absence of distractors. Spatial constraints on selective attention were also investigated by comparing the effect of distractors presented on the same versus opposite side as the target. When attending to touch, the addition of visual distractors had a significantly larger effect on error rates in both of the older groups as compared to the Young group. This indicates that ageing has a detrimental effect on crossmodal selective attention. In all three age groups, performance was impaired when the target and distractor were presented at incongruent as compared to congruent elevations in both tasks. This congruency effect was modulated by the relative spatial location of the target and distractor in certain conditions for the Young and the Young-Old group. That is, participants in the two younger age groups found it harder to attend selectively to targets in one modality, when distractor stimuli came from the same side rather than from the opposite side. However, no significant spatial modulation was found in the Old-Old group. This suggests that ageing may also compromise spatial aspects of crossmodal selective attention.

Visuotactile temporal order judgments in ageing.

We report an experiment on the effects of ageing on crossmodal temporal perception. Young (mean age = 21.7 years) and old (mean age = 75.1 years) participants were presented with pairs of visual and vibrotactile stimuli to either hand and required to make unspeeded temporal order judgments (TOJs) regarding which sensory modality appeared to have been presented first. The stimulus onset asynchrony (SOA) between the two stimuli was varied using the method of constant stimuli. Temporal precision, as indexed by the just noticeable difference (JND), was better (i.e., JNDs were lower) when the stimuli were presented from different positions (M = 101 ms) rather than from the same position (M = 120 ms), as has been demonstrated previously. Additionally, older observers required more time (i.e., their JNDs were larger) to accurately perceive the temporal order (M = 131 ms) as compared to younger observers (M = 98 ms). Our results confirm that ageing deleteriously affects crossmodal temporal processing even when the spatial confound inherent in previous research has been ruled out.

Losses in gross brain volume and cerebral blood flow account for age-related differences in speed but not in fluid intelligence

Age-related gross head size; adjusted age-related change in brain volume and carotid and basilar blood flow; as well as scores on 3 tests of fluid intelligence (gf), 2 tests of information-processing speed, 2 memory tests, and 3 tests of executive function were obtained from 69 volunteers aged from 62 to 84 years. Brain volume negatively predicted scores on all 10 cognitive tasks, accounting for up to 78% of age-related variance in scores on the speed tasks and on 1 executive task. Cerebral blood flow (CBF) negatively predicted scores on 8 cognitive tasks, accounting for up to 36% of age-related variance in speed scores. However, neither brain volume nor CBF accounted for significant age-related variance between individuals on any of 3 gf tests. We conclude that speed, but not gf, is an exceptionally sensitive behavioral index of the progress of gross brain changes that affect cognition in old age and that speed and gf do not reflect integrity of the same functional systems.

Effects of global atrophy, white matter lesions, and cerebral blood flow on age-related changes in speed, memory, intelligence, vocabulary, and frontal function.

Brain images were obtained from 133 healthy people of ages 61-85 years who completed 20 tests of information processing speed, intelligence, frontal and executive function, memory, and vocabulary. Structural equation models examined relationships between cognitive test scores, ages and measurements of global age-associated atrophy, white matter lesions, and cerebral blood flow. These neurophysiological measures jointly account for all age-related variance in information processing speed. Speed entirely mediated relationships between neurophysiological measures and memory and partly mediated relationships between neurophysiological measures and intelligence and frontal function. Neurophysiological measures, but not calendar age, accounted for vocabulary scores. Cognitive slowing was responsible for some, but not all, age-related declines in mental function. Age-related declines in intelligence, frontal function, and speed were due to changes in different functional systems.

Do current beliefs predict hypomanic symptoms beyond personality style? Factor analysis of the hypomanic attitudes and positive predictions inventory (HAPPI) and its association with hypomanic symptoms in a student population.

A self-report scale called the Hypomanic Attitudes and Positive Predictions Inventory (HAPPI) has been developed to assess cognitions that distinguish between bipolar disorder and nonclinical controls (Mansell, 2006; Mansell & Jones, 2006). We recruited 191 undergraduate students to assess the associations between the HAPPI and self-reported past (MDQ; Hirschfeld et al., 2000) and present (ISS; Bauer et al., 1991) bipolar symptoms, and to explore the factor structure of the scale. The HAPPI correlated with past and present symptoms independently of the BIS/BAS subscales (Carver & White, 1994) and the HPS (Eckblad & Chapman, 1986). Five factors of the HAPPI were identified: success activation and triumph over fear, activating response style, reduced social regulation, loss of control when activated, and catastrophic beliefs about internal states. The HAPPI factors showed specific relationships with current bipolar symptoms that largely fitted with predictions based on the model. Further work is required to establish whether they have a causal role.

Overgenerality of autobiographical memory in Alzheimer's disease

OBJECTIVES Overgenerality of autobiographical memory (ABM) is well documented in a range of clinical conditions, particularly in depressed and parasuicidal patients (e.g., Williams, 1996; Williams & Broadbent, 1986). This study extended the investigation to Alzheimers disease (AD), and attempted to identify whether ABM overgenerality in the AD group is specifically expressed through an excess of categoric memories. DESIGN AD sufferers and control participants were compared on their ABM specificity in a cued-recall task. METHOD Ten AD patients and 10 controls, matched for age, gender and educational level, were administered an ABM specificity measure following their mental status assessment. A battery of neuropsychological tests provided an independent estimate of cognitive deficit severity in the following areas: long-term memory, IQ, working memory, processing speed, and verbal fluency. A control for depression was also employed. RESULTS Compared to control participants, AD participants produced significantly fewer specific autobiographical memories. Additionally, the number of produced categoric overgeneral memories was significantly greater in the AD group in comparison with the controls. CONCLUSION This study demonstrates the existence of ABM overgenerality in AD, manifested through an excess of categoric memories. Consistent with the mnemonic interlock theory (Williams, 1996), AD sufferers seem to lack cognitive resources to conduct a directed search for a specific memory, and stop at the categoric descriptions stage. This may contribute to lack of specificity in ABM retrieval.

Relative preservation of 'animate' knowledge in an atypical presentation of herpes simplex virus encephalitis

A comprehensive battery of neuropsychological tests designed to assess primary cognitive functions, including language and semantic memory, was given to MG, a patient with confirmed herpes simplex virus encephalitis. MG’s initial jargon aphasia resolved over time to leave her with a mild phonological impairment. She had a very mild amnesia that was worse for verbal material and a category-specific impairment of semantic memory. This latter impairment resulted in a significant anomia that was worse for manmade/artefact items than for animate kinds. Her naming difficulties were associated with a mild impairment in comprehension that was not specific to category or feature type. MRI revealed a strongly asymmetric and atypical distribution of pathology in MG with the disease affecting the left medial temporal lobe, temporal pole, left frontotemporal and temporoparietal regions.