This study aimed to explore the combined influence of age and cognitive control on the behavioural and electrophysiological indicators of local, restart and mixing costs. Two groups of middle-aged (49-60 y.o., N=40) and older (61-80 y.o., N=40) adults were split according to their overall z-score in a composite of six neuropsychological measures of executive function. All participants performed a task-cueing version of the Wisconsin Card Sorting Test (WCST) adapted for measuring event-related potentials, whereby tonal cues instructed to switch or repeat the task rule. A single-task condition with identical sensory and motor response demands was used to aid interpretation of behavioural and brain responses to cues and target events. Working memory updating of stimulus-response mappings, as putatively indexed by local switch costs and cue-locked P3 activity (350-460 msec post-cue onset), was preserved in both older and low control adults. In turn, low control adults showed larger restart costs and enhanced cue-locked P2 amplitudes (190-250 msec) in the task-switching condition only, suggesting lesser preparatory control in the presence of interference. Low control adults showed comparatively larger mixing costs and smaller cue-locked fronto-central slow negativities (500-700 msec), suggesting an inefficient online maintenance of task-set information over time. In contrast, target-locked brain responses were mostly sensitive to age-related effects, with older adults showing two well-known effects: (1) an "anterior shift" in target P3 activity (350-460 msec), and (2) an attenuation of fronto-central slow negativities in single-task and task-switching conditions, respectively. The additive association found between age and cognitive control for different behavioural indexes of task-switch costs suggests a differential influence of these factors upon two successive information processing stages: individual differences in cognitive control mainly influenced the neural indexes of preparatory task-set activation and maintenance, whereas age-related effects influenced the neural indexes of target response selection and task execution.
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