A Randomized Controlled ERP Study on the Effects of Multi-Domain Cognitive Training and Task Difficulty on Task Switching Performance in Older Adults

Abstract

Executive functions are subject to a marked age-related decline, but have been shown to benefit from cognitive training interventions. As of yet, it is, however, still relatively unclear which neural mechanism can mediate training-related performance gains. In the present electrophysiological study, we examined the effects of multi-domain cognitive training on performance in an untrained cue-based task switch paradigm featuring Stroop color words: participants either had to indicate the word meaning of Stroop stimuli (word task) or perform the more difficult task of color naming (color task). One-hundred and three older adults (>65 years old) were randomly assigned to a training group receiving a 4-month multi-domain cognitive training, a passive no-contact control group or an active (social) control group receiving a 4-month relaxation training. For all groups, we recorded performance and EEG measures before and after the intervention. For the cognitive training group, but not for the two control groups, we observed an increase in response accuracy at posttest, irrespective of task and trial type. No training-related effects on reaction times were found. Cognitive training was also associated with an overall increase in N2 amplitude and a decrease of P2 latency on single trials. Training-related performance gains were thus likely mediated by an enhancement of response selection and improved access to relevant stimulus-response mappings. Additionally, cognitive training was associated with an amplitude decrease in the time window of the target-locked P3 at fronto-central electrodes. An increase in the switch positivity during advance task preparation emerged after both cognitive and relaxation training. Training-related behavioral and event-related potential (ERP) effects were not modulated by task difficulty. The data suggest that cognitive training increased slow negative potentials during target processing which enhanced the N2 and reduced a subsequent P3-like component on both switch and non-switch trials and irrespective of task difficulty. Our findings further corroborate the effectiveness of multi-domain cognitive training in older adults and indicate that ERPs can be instrumental in uncovering the neural processes underlying training-related performance gains.

Keywords: N2; P2; P3; Stroop switch task; aging; cognitive training; switch positivity; task difficulty.

Figure 1

Mean reaction times, error rates and linear integrated speed-accuracy score (LISAS) for the three groups (cognitive training, active control, passive control) as a function of session (pretest, posttest), trial type (single, switch, stay) and task (word task, color task). Error bars indicate the standard error of the mean. Posttest reaction time gains associated with cognitive training are highlighted (**significant at p < 0.001).

Figure 2

Cue-locked grand average event-related potentials (ERPs) for the three groups (cognitive training, active control, passive control) at Fz, Cz and Pz as a function of session (pretest, posttest) and trial type (single, switch, stay). Time scaling ranges from −100 ms to 1100 ms around cue onset and positive deflections are displayed downward. Cognitive training was associated with increased posttest amplitudes of the highlighted cue-locked P3 on stay trials (green lines).

Figure 3

Target-locked grand average ERPs for the three groups (cognitive training, active control, passive control) at Fz, FCz, Cz and Pz as a function of session (pretest, posttest) and trial type (single, switch, stay). Time scaling ranges from −100 ms to 1000 ms around cue onset and positive deflections are displayed downward. Cognitive training was associated with increased posttest amplitudes of the highlighted N2 and decreased amplitudes of the highlighted P3 for all trial types. Single trials (black lines) additionally showed reduced latencies of the highlighted P2 at posttest.