Neuronal Correlates

Besides anatomical changes (Raz, 2000), there is consensus that during the course of normal aging the concentration of neurotransmitters—for instance, dopamine—in the frontal cortex, striatum, and basal ganglia decreases by 5-10% in each decade of life (e.g., Kaasinen et al., 2000). Functional relationships between aging-related deficits in the dopa-minergic system and age-related decrements in various aspects of information processing have also been documented. For instance, the density of dopamine receptors in the ni-grostriatum associates negatively with reaction time (RT)

Working Memory

Working Memory

-O- Backward Digit Span -#- Reading Span -O- Computation Span

Age Group

Processing Speed

Age Group

Processing Speed

B in

-O- Backward Digit Span -#- Pattern Comparison -O- Letter Comparison

20s 30s 40s 50s 60s 70s 80s Age Group

-O- Backward Digit Span -#- Pattern Comparison -O- Letter Comparison

20s 30s 40s 50s 60s 70s 80s Age Group

D2 Receptor in Frontal Cortex i5

45 Age

Figure 2. Aging-related declines in information processing and neurotransmitter density.

Negative adult age differences in working memory (A), processing speed (B), and dopamine D2-like receptor availability in the frontal cortex (C). Source: Data based on Park et al. (1996) and Kaasinen et al. (2000); figure adapted from Li, Lindenberger, & Sikstrom (2001).

and positively with RT variance (Spirduso, Mayfield, Grant, & Schallert, 1989). Other studies have demonstrated that WM function is reduced in aged monkeys due to attenuated dopaminergic function (for review see Arnsten, 1998).

Recent neurocomputational approaches provide computational explications for linking aging-related decline in neuromodulation and cognitive deficits. For instance, simulations show that declines in dopaminergic modulation could be related to reduced neural information-processing fidelity, cortical representation distinctiveness, and various aspects of cognitive aging deficits (S.-C. Li, Lindenberger, & Sikstrom, 2001). Other models relate deficits in dopamine modulation more specifically to aging effects on memory context representation and maintenance (Braver et al., 2001) and on error processing (Nieuwenhuis et al., 2002).

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