Neuroanatomical substrates of age-related cognitive decline

There are many reports of relations between age and cognitive variables and of relations between age and variables representing different aspects of brain structure and a few reports of relations between brain structure variables and cognitive variables. These findings have sometimes led to inferences that the age-related brain changes cause the age-related cognitive changes. Although this conclusion may well be true, it is widely recognized that simple correlations are not sufficient to warrant causal conclusions, and other types of correlational information, such as mediation and correlations between longitudinal brain changes and longitudinal cognitive changes, also have limitations with respect to causal inferences. These issues are discussed, and the existing results on relations of regional volume, white matter hyperintensities, and diffusion tensor imaging measures of white matter integrity to age and to measures of cognitive functioning are reviewed. It is concluded that at the current time the evidence that these aspects of brain structure are neuroanatomical substrates of age-related cognitive decline is weak. The final section contains several suggestions concerning measurement and methodology that may lead to stronger conclusions in the future.     

The information-loss model: a mathematical theory of age-related cognitive slowing

A model of cognitive slowing is proposed with the following assumption: Information is lost during processing, processing occurs in discrete steps with step duration inversely related to the amount of information currently available, and the effect of aging is to increase the proportion of information lost per step. This model correctly predicts a positively accelerated relation between latencies of older and younger adults and provides a unified account of the effects of task complexity, practice, speed-accuracy tradeoffs, and fluctuations in individual performance. Strong support for the thesis that cognitive slowing is global, and not localized in specific age-sensitive components, is provided by the fact that the model accurately predicts the latencies of older adults on the basis of those of younger adults, without regard to the nature of the task, across a latency range of nearly 2 orders of magnitude.     

Executive functioning as a potential mediator of age-related cognitive decline in normal adults

Critical requirements for the hypothesis that executive functioning is a potential mediator of age-related effects on cognitive functioning are that variables assumed to reflect executive functioning represent a distinct construct and that age-related effects on other types of cognitive functioning are reduced when measures of executive functioning are statistically controlled. These issues were investigated in a study involving 261 adults between 18 and 84 years of age. Although age-related effects on various cognitive abilities were substantially reduced after statistical control of the variance in measures hypothesized to represent executive functioning, there was only weak evidence for the existence of distinct constructs corresponding to executive functioning or to aspects of executive control concerned with inhibition, updating, or time sharing.     

Computational explorations of the influence of structured knowledge on age-related cognitive decline

Experience in a domain can sometimes offset cognitive declines that occur with aging. Using a series of neural network simulations of learning chess opening positions, the authors investigated how structured knowledge in a distributed representation may influence age-related declines. Aging manipulations implemented as modulations of neural noise showed increased knowledge as being protective of performance on a chess memory span task, whereas changes in neural plasticity and neural loss lead to main effects without interactions and steeper declines for the initially more able. The models could also simulate the increase in variability in older groups.     

Multiple systems: A new approach to cognitive theory

Abstract

Cognitive processes turn out to be both more innate and more culturally based than we used to think. On the one hand, ecological and interpersonal perception are innately prepared, available in infancy; on the other, mental development depends critically on social support. Taken together with the emerging multiple/modular structure of the brain, these discoveries demand a new kind of cognitive theory: an ecologically grounded, developmental account of distinct systems in interaction. Three such systems, primarily perceptual in function, are described here: (1) direct perception/action establishes an immediate non-representational sense of self and environment that grounds all other cognition; (2) interpersonal perception/reactivity produces species-specific patterns of social interaction; (3) recognition/representation identifies and classifies what is perceived. These systems are distinguished by neurological as well as psychological criteria: the neuroanatomical “where/what” distinction, for example, reflects the difference between direct perception and recognition. Cooperation among these three systems, which begins near the end of the first year, is basic to language and other forms of cultural learning.     

Older adults' decoding of emotions: role of dynamic versus static cues and age-related cognitive decline

Although age-related deficits in emotion recognition have been widely explored, the nature and scope of these deficits remain poorly understood. We conducted two experiments to examine whether these deficits are less pronounced when older adults evaluate dynamic compared with static images, and second, whether age-related cognitive decline exacerbates these deficits. Our results suggest that age-related cognitive decline exacerbates older adults' deficits in detecting anger, but only from static faces. Furthermore, older adults do not show emotion recognition deficits when evaluating global emotions from dynamic images of faces.     

Rock's cognitive theory of illusory figures: a commentary.

Contrary to a previously published opinion, the 'cognitive' theory of illusory contours is rich in detail and empirical support.     

Sensitivity of the informant questionnaire on cognitive decline: an application of item response theory

The Informant Questionnaire on Cognitive Decline (IQCODE) is a formal informant report instrument, originally developed by Jorm and Jacomb (1989; Psychological Medicine, 19(4), 1015). The goal of the present study was to evaluate the range of cognitive decline in which the IQCODE is most sensitive, using item response theory (IRT). Existing data (N = 740) from a sample of community-dwelling older adults was used for this purpose. A 2-parameter model estimating item difficulty and discrimination fit the data best. Additionally, the IQCODE provided the most psychometric information in the range of -0.5 < theta < 1.5, with peak information obtained at approximately theta = 0.4. Based on individuals' latent score (theta) estimates, items on the IQCODE are adequate for use as a screening tool for dementia. Results of the item calibration may be useful for targeted assessment needs, such as the development of short forms.     

Weeping: Evidence for a cognitive theory

According to a two-factor cognitive theory of weeping, schema-incongruent information and efforts to assimilate it create arousal; resolution, giving up of the schema, and cessation of the assimilation efforts result in arousal reduction and may be associated with emotional tears. To assess these predictions, female subjects were shown an emotional film under one of two conditions. In one condition only schema-induction and incongruity phases were viewed, while the other condition viewed the complete film (i.e., schema-induction, incongruity, and resolution). Consistent with expectations, incongruity was associated with increased stress and depressed mood. Only subjects who viewed the complete film reported significant decreases in these states. The final scene, assumed to trigger schema change, produced the greatest amount of weeping.This paper is adapted from a portion of a doctoral dissertation conducted by the first author. We gratefully acknowledge the assistance of Walter Katkovsky and Raymond Ditrichs. A version of this paper was presented at a meeting of the Western Psychological Association, May 1986.     

Environmentally induced analgesia: age-related decline in a neurally mediated, nonopioid system

In order to examine the function of an endogenous system of pain inhibition during aging, rats (3, 14, and 24 months old) were exposed to 90 s of hind-paw shock. To investigate the pharmacology and anatomy involved in the production of hind-paw shock induced analgesia, the effects of naltrexone (7 mg/kg), scopolamine (5 mg/kg), and adrenalectomy were examined. Results revealed that there was an age-related reduction in the degree of analgesia produced by hind-paw shock. Naltrexone and adrenalectomy did not alter the analgesia elicited by hind-paw shock. Scopolamine reduced the analgesia produced by hind-paw shock, and the effectiveness of scopolamine blockage declined with age. The results of a second experiment demonstrated that the effect of scopolamine was specific to the analgesia induced by hind-paw shock because scopolamine was ineffective in modifying the analgesia produced by a different stressor (cold water). These results suggest that the decline in hind-paw shock induced analgesia is the result of an alteration in the function of the cholinergic system.     

Double forced compliance: a new paradigm in cognitive dissonance theory.

An experiment was conducted with a new paradigm of Festinger's (1957) theory of dissonance. This paradigm was used to test dissonance reduction following two behaviors, rather than just one as in the classic forced compliance paradigm. The first behavior involved refraining from smoking for one evening, and the second, convincing a peer that abstinence from smoking was not difficult. It was hypothesized that the dissonance reduction effect would be greater for a sample of French students who had executed both behaviors than for those who had executed only one. The results supported this hypothesis.     

Stagewise cognitive development: an application of catastrophe theory.

In this article an overview is given of traditional methodological approaches to stagewise cognitive developmental research. These approaches are evaluated and integrated on the basis of catastrophe theory. In particular, catastrophe theory specifies a set of common criteria for testing the discontinuity hypothesis proposed by Piaget. Separate criteria correspond to distinct methods used in cognitive developmental research. Such criteria are, for instance, the detection of spurts in development, bimodality of test scores, and increased variability of responses during transitional periods. When a genuine stage transition is present, these criteria are expected to be satisfied. A revised catastrophe model accommodating these criteria is proposed for the stage transition in cognitive development from the preoperational to the concrete operational stage.     

The mapping model: a cognitive theory of quantitative estimation

How do people make quantitative estimations, such as estimating a car's selling price? Traditionally, linear-regression-type models have been used to answer this question. These models assume that people weight and integrate all information available to estimate a criterion. The authors propose an alternative cognitive theory for quantitative estimation. The mapping model, inspired by the work of N. R. Brown and R. S. Siegler (1993) on metrics and mappings, offers a heuristic approach to decision making. The authors test this model against established alternative models of estimation, namely, linear regression, an exemplar model, and a simple estimation heuristic. With 4 experimental studies the authors compare the models under different environmental conditions. The mapping model proves to be a valid model to predict people's estimates.     

Towards a cognitive theory of existential meaning

The capacity to attribute meaning to personal experiences may rest on a specialized cognitive system enabling this form of causal reasoning. Close examination of these attributional tendencies suggests that this system may be distinct from those underlying other forms of causal reasoning such as a “theory of mind” system in the behavioral domain, a folk physics system in the physical domain, and a folk biology system in the biological domain. A fourth, existential domain, an abstract ontological frame within which the subjective, narrative self is envisioned to be contained, may have driven the construction of an intuitive capacity in humans that encourages them to search for the underlying purpose or reason for having had certain life experiences. This system likely has specific, definable operational rules that are responsible for activating such explanatory searches. In addition, it appears anchored to a general intentionality system that promotes the attribution of teleological purpose and higher-order mental states to an abstract agency that is envisioned to cause events and personal experiences. Identifying the component parts of this specialized cognitive system through empirical investigations can help researchers to reconstruct both its evolutionary phylogeny and to track its developmental emergence.     

Further evidence for a dissociation between different forms of mnemonic expressions in a mouse model of age-related cognitive decline: effects of tacrine and S 17092, a novel prolyl endopeptidase inhibitor

It has been demonstrated previously on the radial maze that the emergence of an age-related mnemonic impairment is critically dependent on the form which the discrimination problems took. Hence, when the arms were presented one by one (i.e., successive go-no-go discrimination), both adult and aged mice learned to distinguish between positive (baited) and negative (unbaited) arms readily, as evidenced by their increased readiness to enter positive relative to negative arms (i.e., by a differential in arm-entry latencies). A selective impairment in the aged mice was seen when these arms were presented subsequently as pairs, such that the mice were confronted with an explicit choice (i.e., simultaneous 2-choice discrimination). When discriminative performance was measured by the differential run speed between positive and negative arms, aged mice were also impaired. This was particularly pronounced in the 2-choice discrimination condition. We examined the effects of tacrine (3mg/kg, subcutaneously) or S 17092 (10mg/kg, orally) in aged mice on the three behavioral indices of this 2-stage spatial discrimination paradigm. The results indicated that: (1) Tacrine, but not S 17092, enhanced the acquisition of go-no-go discrimination as reflected in arm-entry latencies; (2) both drugs improved choice accuracy in simultaneous discrimination, although the effect of tacrine was less striking and, in particular, far from statistical significance in the very first 2-choice responses; and (3) neither drugs significantly affected run-speed performance. We conclude further that the specific patterns of drug effects on the three indices of discriminative performance might suggest that each index is associated with a distinct form of mnemonic expression relying on separate neural systems.     

CGS 5649 B, a new compound, reverses age-related cognitive dysfunctions in rats.

CGS 5649 B improves the learning performance of aged rats in a one-way active-avoidance situation. If, under reversed conditions, treated aged rats are also tested for passive avoidance, they show "place learning," which our findings have demonstrated to be typical of young rats. The effects of the substance are not confined to these experimental models nor are they species specific: it also facilitates passive avoidance in mice and social learning in rats. The compound is effective if administered before or immediately after the learning trial.     

Towards a theory of algorithm-determined cognitive test construction

A rationale for, and data from, a trial of a theory of item generation by algorithms whose origins are cognitive models of task performance are presented. Since Spearman (1904), intelligence has been operationally defined and assessed in human subjects by administering identical test items whose content and order have been fixed only after empirical iterations. In our approach, intelligence is ostensively defined by theoretically determined algorithms used for item construction and presentation. Knowledge of what cognitive factors limit human performance makes it possible to vary within tightly specified parameters those features of the tasks that contribute to difficulty, which we call radicals, to let those components of the tasks that do not contribute to difficulty vary randomly, and to counterbalance aspects of answer production that might induce biases of response. Empirical data are based on the generation of five different short tests demanding only functional literacy as a prerequisite for their execution. Four parallel forms of each test were administered to young male Army recruits whose scores were collated with their Army Entrance Test results, which were not previously known to us. Results show that the parallel, algorithm-generated item sets are statistically invariant, which item generation theory demands; and that the individual tests differentially predict Army Entrance Test scores. We conclude that IQ test performances are parsimoniously explained by individual differences in encoding, comparison and reconstructive memory processes.     

On the relative role of inhibition in age-related working memory decline

In this cross-sectional study, the mediating role of inhibition relative to speed in age-related working memory decline on different tasks was investigated. It was hypothesized that the role of inhibition is marginal or absent in a relatively "passive" or simple working memory task, but present in a relatively "active" or complex task in which the processing, rather than the storage capacity of working memory, is addressed. This hypothesis was tested with a structural equation model that was fitted on a subsample (N = 213) of the Maastricht Aging Study (MAAS). The first trial of the Verbal Learning Test (VLT) served as the passive test and the Self-Paced Auditory Serial Addition Task (SPASAT) as the active test. Results showed that the role of inhibition was absent in predicting VLT performance, whereas it was comparable to the role of speed in predicting SPASAT performance. These findings suggest a relative, task-dependent role of inhibition in explaining age-related memory decline.     

Multiple systems for cognitive control: evidence from a hybrid prime-Simon task

Cognitive control resolves conflicts between appropriate and inappropriate response tendencies. Is this achieved by a unitary all-purpose conflict control system, or do independent subsystems deal with different aspects of conflicting information? In a fully factorial hybrid prime-Simon task, participants responded to the identity of targets displayed at different nominally irrelevant screen locations, preceded by nominally irrelevant, consciously or nonconsciously perceived primes. The response required by the target's identity could match or mismatch (a) the target's location, and (b) the prime's identity, resulting in potential conflict (a) across and (b) within stimulus domains. Conflict effects were investigated within and across trials. Results suggest that (i) nonconsciously perceived information elicits within-trial control, but--unlike consciously perceived information--no across-trial behavioral modulation; (ii) separate subsystems deal with conflicts arising from different stimulus domains; and (iii) occasional apparent interactions between domains reflect a particular difficulty in reactivating a just-discarded response (reactivation aversion effect, RAE).