Electrophysiological investigations of set-shifting in older human adults

Older adults show deficits in tasks of set-shifting. Yet, many underlying cognitive functions are required during such tasks and it is currently unknown which of these mechanisms may be deficient in older age. Here, we investigated this question in a preliminary dataset of 45 young participants (age: 25.2 ± 4.3) and 26 older participants (age: 68.1 ± 5.0) in an EEG-compatible set-shifting paradigm. We were particularly interested in two posterior components: 1) The P300 is a positive component that appears approximately 300 ms to 500 ms after the cue and has a lower amplitude during set-shifting. Its underlying mechanism is the orienting of attentional resources to the stimuli that eliminate rule uncertainty. 2) The Posterior Switch Positivity (PSP) reaches its highest values during a set shift around 500 to 1000 ms after the stimulus and represents the shifting of cognitive sets. Here, we investigated which of these components may be altered in older adults. Behaviourally we found slower reaction times and higher error rates with increasing set-shifting difficulty in both age groups. Older adults, however, showcased higher switch costs. In the EEG data, we found a lower mean amplitude of the P300 during set-shifting in both age groups, with older adults exhibiting solely a higher P300 latency. Most importantly: in contrast to young adults, older adults showed no PSP modulation during set-shifting. Our results indicate that the deficits in set-shifting in older adults can be attributed to alterations of the mechanism underlying the PSP, not the P300.