The temporal trajectory of age-related decreases in executive function

1. The temporal trajectory of age-related decreases in executive function Doreen Nessler¹, Ray Johnson, Jr.², Michael Bersick¹ and David Friedman¹ ¹ Cognitive Electrophysiology Laboratory, NY Psychiatric Institute, NY, NY; ² Department of Psychology, Queens College/ CUNY, Flushing, NY Mixing costs Results Task-switching studies indicate an age-related decrease in working memory (or episodic memory [1]): Older adults’ reaction times (RTs) show a larger increase when maintaining two task sets (in a mixed block) vs. one (mixing costs). In contrast, age has a smaller impact on task-set reconfiguration: The RT difference in mixed blocks between task-set repetitions and switches to an alternative task (switch costs) is age-invariant. However, these results vary with the following task characteristics: switch frequency [2], informative cue occurrence [3] and predictability [4]. Here, we clarify the link between these characteristics and age-related changes, and examine whether some aspects of cognitive control, such as working memory and task-set re-configuration, are compromised at an earlier age than others. Informative Cue Equiprobable, uninformative cue Equiprobable, informative cue Informative Cue Rare switch, uninformative cue Young Young-old Old-old Fig. 2a,b: For all manipulations, young-old and old-old adults similarly showed larger mixing costs than the young. Fig. 2b: Young and young-old, but not old-old, adults used predictability to decrease mixing costs in the equiprobable, uninformative switch condition (see arrows). Rare switch, informative cue Cue- related P3 target P3 4a Cz Cz Introduction Cz 2a Cue Pure task Uninformative Cue Uninformative Cue Pre-switch Switch -1000 Target 1000 ms 4b Equiprobable, predictable Equiprobable, unpredictable Cz Cz Cz Rare switch, predictable Rare switch, unpredictable Switch costs Fig. 4a, b: The age-related increase in mixing cost (Fig. 2a, b) was associated with a larger decrease in target P3 amplitude, most likely reflecting task-set configuration processes that were not prepared before target onset. (a) Despite age-invariant P3 amplitudes to the cue, only older adults show a decrease in target P3 for pre-switch and switch trials compared to pure trials. (b) Only the young show a smaller decrease in the target P3 for pre-switch than switch trials. Informative Cue Participants: 15 Young (age 18 to 30); 15 Young-old (age 60 to 68); 15 Old-old (age 72 to 87) Design: Digit (not 5) required response: more/less than 5? or odd/even? pure blocks: one task; mixed blocks: two tasks. Factors: (1) Ratio of switch (S) to stay or repeat (R) trials equiprobable; switch after 0, 1, or 2 trials: a-bb-aaa rare switch 1:3; switch after 2, 3, or 4 trials: aaa-bbbb-aaaaa (2) Cue-status: informative, uninformative; (3) Predictability Status: predictable, unpredictable Mixing costs = pre-switch RTs in mixed blocks - RTs in pure blocks Switch costs = switch RTs – pre-switch RTs mixed blocks EEG recording: 62 sintered Ag/AgCl electrodes; ref.: averaged mastoids; continuous DC-100Hz; 500 Hz sampling rate; Fig. 1: ERP epochs. 2b 3a Uninformative Cue Fig. 3a, b: Similarly,for young-old and old-old adults, differences in switch costs compared to the young were only present for rare switches after uninformative cues (see arrows), which is when task demands were highest. Methods Fig. 5: For equipro-bable, uninformed items, the decrease in target P3 was smaller for pre-dictable than for unpredictable trials, most likely reflec-ting advanced pre-paration (Fig. 2b), for young and young-old, but not old-old adults. Young Young-old Old-old 3b Target onset Fig. 7: Response conflict for older adults, as indicated by MFN amplitude, was high regardless of task demands. The older adults’ impairment in detecting increased conflict induced by rare, uninformed switches may be due to their having a limit on the amount of conflict that they can detect (Fig. 3b). Baseline for cue- related ERPs Pure task Young Young-old Old-old Cz Cz Cz Predictable trials Unpredictable trials 300 800 1300 0 500 1000 ms 1 Cue onset 0 500 1000 ms Baseline for target-related ERPs (collapsed over pre-switch, switch, post-switch) 5 Fz Fz Fz Young-old Old-old Young Behavioral and ERP results indicate that the ability to maintain two task sets in memory declines early in the aging process (young-old), independent of task characteristics. However, the ability to use working memory for advanced task preparation when the upcoming task is predictable remains intact until later in the aging process. Task-set reconfiguration seems to be intact when task demands are low, but compromised for rare, uninformed switches for both groups of older adults. The age-related decrease in the ability to reconfigure the task set could be due to difficulties in 1) detecting the increased conflictand/or 2) upregulating and increasing cognitive control. MFN -200 200 400 ms Fig. 6: The age-related increase in switch costs for rare uninformed switches (Fig. 3b) was associated with the lack of a significant decrease in target P3. baseline Response 7 Discussion FCz FCz FCz 6 [1] Mayr & Kliegl, 2000, JEP: Learning, Memory, and Cognition, 26, 1124-1140. [2] Friedman, Nessler, Johnson, Ritter & Bersick, in revision. [3] Kray, Li & Lindenberger , 2002, Brain and Cognition, 49, 363-381. [4] Van Asselen & Ridderinkhof, 2000, Psychologica Belgica, 40, 259–273. References 0 500 1000 ms Pure task Equiprobable, uninformative cue Rare switch, uninformative cue