Altered theta distribution and coherence during set-shifting in older age

Cognitive flexibility is an executive function that enables adapting behaviour to a changing environment and is thus critical for daily life. The degree of its preservation upon healthy aging and the neural mechanisms underlying it are still a matter of debate. To investigate the electrophysiological correlates of cognitive flexibility in older age, we measured cognitive flexibility in 99 young (24.75 ± 4.45 years) and 83 older adults (69.19 ± 6.25) using electroencephalography (EEG). Compared to young adults, older adults showed a more conservative response pattern with longer reaction times, but lower error rates (speed-accuracy tradeoff). In the EEG, both age groups exhibited increased theta-power during set-shifting, with a fronto-central peak in the young, but a more fronto-lateral topography in older adults. Importantly, both groups displayed increases in theta coherence and global efficiency during set-shifting. Coherence modulations were restricted in frontocentral areas in the young but were diminished and distributed across the scalp in the older. Better set-shifting performance was most strongly associated with higher coherence in older adults and with global efficiency in both age groups. These results point to age-related differences in cortical processing underlying cognitive flexibility, which involve the employment of more distributed neural resources for successful task completion.