Older adults compensate for switch, but not mixing costs, relative to younger adults on an intrinsically cued task switching experiment

Abstract

Introduction: Aging negatively impacts the ability to rapidly and successfully switch between two or more tasks that have different rules or objectives. However, previous work has shown that the context impacts the extent of this age-related impairment: while there is relative age-related invariance when participants must rapidly switch back and forth between two simple tasks (often called "switch costs"), age-related differences emerge when the contexts changes from one in which only one task must be performed to one in which multiple tasks must be performed, but a trial-level switch is not required (e.g., task repeat trials within dual task blocks, often called "mixing costs"). Here, we explored these two kinds of costs behaviorally, and also investigated the neural correlates of these effects.

Methods: Seventy-one younger adults and 175 older adults completed a task-switching experiment while they underwent fMRI brain imaging. We investigated the impact of age on behavioral performance and neural activity considering two types of potential costs: switch costs (dual-task switch trials minus dual-task non-switch trials), and mixing costs (dual-task non-switch minus single-task trials).

Results: We replicated previous behavioral findings, with greater age associated with mixing, but not switch costs. Neurally, we found age-related compensatory activations for switch costs in the dorsal lateral prefrontal cortex, pars opercularis, superior temporal gyrus, and the posterior and anterior cingulate, but age-related under recruitment for mixing costs in fronto-parietal areas including the supramarginal gyrus and pre and supplemental motor areas.

Discussion: These results suggest an age-based dissociation between executive components that contribute to task switching.

Keywords: aging; compensation; costs; executive processes; task switching; working memory.

Figure 1

Schematic of the fMRI task. Participants received an instruction cue followed by 12 trials in which they used their left and right index fingers to indicate their response. The color of the letter indicated which task—Vowel/Consonant (green) or Upper/Lower (red) cased or NoGo (white)—should be performed. Panel (A) represents both types of single-task blocks, in which only one of the two tasks sets were cued. Panel (B) represents a dual-task block, in which participants alternated between the two different tasks.

Figure 2

Switching and Mixing Costs for (A) accuracy and (B) reaction time for correct trials. For accuracy, switching costs were calculated as the difference between Dual No Switch Trials and Dual Switch Trials, and mixing costs were calculated as the difference between Dual No Switch Trials and Single- task Trials. For RT, cost was calculated in the reverse (switching costs were calculated as the difference between Dual Switch Trials and Dual No Switch Trials, and mixing costs were calculated as the difference between Single-task Trials and Dual No Switch Trials). In both cases, a higher value indicates a greater cost. Error bars are standard error of the mean. *p <.05.

Figure 3

Activations for younger and older adults, separately, for switching and mixing costs. (A) Younger Switching Cost; (B) Older Switching Cost; (C) Younger Mixing Cost; and (D) Older Mixing Cost. Only the five largest clusters for each contrast are rendered. Details of each cluster are shown in Table 1, with colors representing separate clusters according to size: Cluster 1 = Red, Cluster 2 = Blue, Cluster 3 = Green, Cluster 4 = Yellow, Cluster 5 = White.

Figure 4

Activations from age-group level contrasts for switching and mixing costs. (A) Younger > Older Switching Cost; (B) Older > Younger Switching Cost; (C) Younger > Older Mixing Cost; and (D) Older > Younger Mixing Cost. Only the five largest clusters for each contrast are rendered. Details of each cluster are shown in Table 2, with colors representing separate clusters according to size: Cluster 1 = Red, Cluster 2 = Blue, Cluster 3 = Green, Cluster 4 = Yellow, Cluster 5 = White.