Age-related changes in electrophysiological and neuropsychological indices of working memory, attention control, and cognitive flexibility

Abstract

Older adults exhibit great variability in their cognitive abilities, with some maintaining high levels of performance on executive control tasks and others showing significant deficits. Previous event-related potential (ERP) work has shown that some of these performance differences are correlated with persistence of the novelty/frontal P3 in older adults elicited by task-relevant events, presumably reflecting variability in the capacity to suppress orienting to unexpected but no longer novel events. In recent ERP work in young adults, we showed that the operation-span (OSPAN) task (a measure of attention control) is predictive of the ability of individuals to keep track of stimulus sequencing and to maintain running mental representations of task stimuli, as indexed by the parietally distributed P300 (or P3b). Both of these phenomena reflect aspects of frontal function (cognitive flexibility and attention control, respectively). To investigate these phenomena we sorted both younger and older adults into low- and high-working memory spans and low- and high-cognitive flexibility subgroups, and examined ERPs during an equal-probability choice reaction time task. For both age groups (a) participants with high OSPAN scores were better able to keep track of stimulus sequencing, as indicated by their smaller P3b to sequential changes; and (b) participants with lower cognitive flexibility had larger P3a than their high-scoring counterparts. However, these two phenomena did not interact suggesting that they manifest dissociable control mechanisms. Further, the fact that both effects are already visible in younger adults suggests that at least some of the brain mechanisms underlying individual differences in cognitive aging may already operate early in life.

Keywords: P300; aging; cognitive flexibility; event related brain potentials; fluid intelligence; operation-span task; working memory.

Figure 1

Reaction time (RT; top) and P300 sequential trees (bottom). Trees indicate the RT/P300 amplitude elicited by stimulus X as a function of the preceding two stimuli (1-back, 2-back in the sequential trees) for the various subject groupings. In the RT trees, the ordinate is time in milliseconds; in the P300 trees, the ordinate is the amplitude of the P300 in microvolts. The four different colors represent the four possible sequential conditions (with the underlined X indicating the current stimulus).

Figure 2

Grand average waveforms of stimulus X as a function of the preceding two stimuli for the Fz, Cz, and Pz electrode sites for younger and older adults split into high- and low OSPAN groups. Solid line: no change condition (XXX, where X is the current stimulus); dashed line: most extreme change condition (OOX, where X is the current stimulus).

Figure 3

Grand average waveforms of stimulus X as a function of the preceding two stimuli for the Fz, Cz, and Pz electrode sites for younger and older adults split into high- and low-RPM groups. Solid line: no change condition (XXX, where X is the current stimulus); dashed line: most extreme change condition (OOX, where X is the current stimulus).

Figure 4

Subtraction waveforms at Pz (condition OOX minus condition XXX, where X is the stimulus being averaged as a function of the preceding sequence). The younger adult group is shown on the left and the older adult group on the right; top: subjects are sorted into high- and low OSPAN groups; bottom: subjects are sorted into high- and low-RPM groups. Note the larger P300 to stimulus change for both low OSPAN groups, and the smaller (and in fact inverted) effect for the RPM groups.

Figure 5

Effects of age, cognitive flexibility (RPM) and working memory capacity (OSPAN) on the similarity across midline electrodes (top) and on the relative frontality of the P300 distribution (bottom). Error bars refer to the SE of the mean. LR, low-RPM group; HR, high RPM group; LO, low OSPAN group; HO, high OSPAN group; YA, Younger adults; OA, older adults.