Fig. 1.

Individual frontal theta frequency and Simon task behavioural performance. The Simon effect quantifies the temporal cost of successfully resolving spatial conflict caused by hearing a word in the ear opposite to its corresponding spatial meaning. A larger Simon effect indicates slower conflict resolution and, therefore, less inhibitory control^37,38,58. (a) The Simon effect exhibited a negative correlation with f_θ, indicating that higher f_θ values were associated with a smaller Simon effect. (b) The f_θ was significantly lower in the older adults, coinciding with a considerably larger Simon effect (c), suggesting less efficient inhibitory control. A separate auditory recognition task was utilized to test the task dependency of f_θ. The task used the same stimuli with different instructions, resulting in significantly different f_θ (see Supplementary Fig. S4 for EEG time–frequency analyses and topographies). However, the significant correlation between task performance and frequency was maintained (Supplementary Fig. S5). This suggests that the individual f_θ is task dependent.