Trends in Cognitive Sciences
Volume 5, Issue 11, 1 November 2001, Pages 479-486
Journal home page for Trends in Cognitive Sciences

Opinion
Aging cognition: from neuromodulation to representation

https://doi.org/10.1016/S1364-6613(00)01769-1Get rights and content

Abstract

Basic cognitive functions, such as the abilities to activate, represent, maintain, focus and process information, decline with age. A paradigm shift towards cross-level conceptions is needed in order to obtain an integrative understanding of cognitive aging phenomena that cuts across neural, information-processing, and behavioral levels. We review empirical data at these different levels, and computational theories proposed to enable their integration. A theoretical link is highlighted, relating deficient neuromodulation with noisy information processing, which might result in less distinctive cortical representations. These less distinctive representations might be implicated in working memory and attentional functions that underlie the behavioral manifestations of cognitive aging deficits.

Section snippets

Cognitive aging phenomena at different levels

Since the first studies on adult age differences in intellectual functioning were published in the 1920s (e.g. Ref. 2), cognitive aging phenomena have been studied at various levels (see Fig. 1). At the behavioral level, individual difference researchers have documented aging-related declines in many psychometric measures of fluid intelligence 3 (i.e. basic cognitive mechanics 4 for memorizing, reasoning, and learning). Furthermore, aging-related increases of intra-individual variability,

Aging, information processing, and neuromodulation

Aging affects three main facets of information processing. People's abilities to activate, to represent and maintain information in mind, to attend to relevant but ignore irrelevant information, and to process information promptly decline with advancing age. At the neurobiological level, the efficacy of neuromodulation also declines. Among various neurotransmitter systems, we focus on the monoamines (e.g. serotonin and the catecholamines, particularly dopamine and noradrenaline) 15, 16, 17, 18,

Recent computational theories linking neuromodulation with cognitive aging

In 1990, two mathematical theories of cognitive aging were proposed in part to resolve the interdependence and circularity problems facing the resource-reduction theories 47, 48. Although not operating at the level of neuromodulation, both theories foreshadowed cross-level conceptual orientation. The network-disconnection theory of aging and information-processing rate 47 makes broad reference to neuroanatomical changes that might involve the degeneration of axonal connections. The

From deficient neuromodulation to neural noise

A classical hypothesis of cognitive aging at the neurobiological level is increased neural noise (haphazard activation during neuronal information processing) 50. However, thus far, mechanisms leading to such an increase and its proximal and distal consequences have not been unveiled. Simulating aging-related decline of dopaminergic neuromodulation by attenuating the G parameter in neural networks hints at a possible chain of mechanisms relating deficient neuromodulation to increased neural

Less distinctive cortical representations

The computational simulations further show that as reduced responsivity leads to increased intra-network random activation variability, another subsequent effect is a decrease in the distinctiveness of the network's internal representations. Low representational distinctiveness means that the activation profiles formed across the network's hidden units for different stimuli are less readily differentiable from each other. To illustrate this, Fig. 3c shows the internal activation patterns

Implications: a paradigm shift towards co-evolving fields across levels

Details regarding the involvement of neuromodulation in cognitive aging deficits remain to be unraveled. Pieces of the puzzle are emerging in various sub-fields, and the field as a whole could benefit from a paradigm shift towards overarching frameworks seeking to integrate cognitive aging phenomena across different levels. The proposed theoretical link – from attenuated neuromodulation to increased neural noise and less distinctive cortical representations in the aging brain, and finally on to

Acknowledgements

The authors are grateful to Valtteri Kassinen and Denise C. Park for permitting the redrawing of some data from their studies. We thank Todd S. Braver for helpful e-mail exchanges about the relations between his theory and ours. We are grateful to Naftali Raz, the anonymous reviewers, and Julia Delius for their many helpful comments on an earlier version of this article. We thank Peter A. Frensch for previous contributions to related work, and Paul B. Baltes and the Max Planck Institute for

References (59)

  • A.M. Graybiel

    Neurotransmitters and neuromodulators in the basal ganglia

    Trends Neurosci.

    (1990)
  • D.C. Rubin

    Frontal-striatal circuits in cognitive aging: evidence for audate involvement

    Aging Neuropsychol. Cognit.

    (1999)
  • P.S. Goldman-Rakic

    D1 Receptors in prefrontal cells and circuits

    Brain Res. Rev.

    (2000)
  • J. Cerella

    Aging and information-processing rate

  • V. Kannisto

    Development of Oldest-old Mortality, 1950–1990: Evidence from 28 Developed Countries

    (1994)
  • J.C. Foster et al.

    The applicability of mental tests to persons over 50

    J. Appl. Psychol.

    (1920)
  • J.L. Horn

    The theory of fluid and crystallized intelligence in relation to concepts of aging in adulthood

  • P.B. Baltes

    Theoretical propositions of lifespan developmental psychology: on the dynamics between growth and decline

    Dev. Psychol.

    (1987)
  • S-C. Li et al.

    Cross-level unification: a computational exploration of the link between deterioration of neurotransmitter systems and dedifferentiation of cognitive abilities in old age

  • T.A. Salthouse

    Theoretical Perspectives on Cognitive Aging

    (1991)
  • N. Raz

    Aging of the brain and its impact on cognitive performance: integration of structural and functional findings

  • P.S. Churchland et al.

    Perspectives on cognitive neuroscience

    Science

    (1988)
  • D.L. Schacter

    Understanding implicit memory

    Am. Psychol.

    (1992)
  • Braver, T.S. et al. Context processing in older adults: evidence for a theory relating cognitive control to...
  • S-C. Li

    Unifying cognitive aging: from neuromodulation to representation to cognition

    Neurocomputing

    (2000)
  • Li, S-C. Connecting the many levels and facets of cognitive aging. Curr. Dir. Psychol. Sci. (in...
  • D.F. Wong

    Effects of age on dopamine and serotonin receptors measured by positron tomography in the living human brain

    Science

    (1984)
  • Cited by (688)

    View all citing articles on Scopus
    View full text