To provide more detailed information on the relationships between PAC and behavior, we performed regression analyses at the individual subject level. As shown in Figure 3e, younger adults with stronger theta-gamma PAC performed the task with higher accuracy, relative to individuals with weaker coupling (r41 = 0.611, p < 0.01). In contrast, older adults showed no significant relationship between performance accuracy and theta-gamma PAC collapsed across left temporal electrodes (r41 = 0.188, p = 0.233). The results suggest that theta-gamma PAC in younger adults is behaviorally significant, predictive of subsequent working memory success. However, when theta-gamma rhythms become largely uncoupled, as in the brains of older people, PAC appears to lose its behavioral usefulness in driving cognitive performance.
