Theta and alpha oscillations as signatures of internal and external attention to delayed intentions: A magnetoencephalography (MEG) study

Abstract Background Remembering to execute delayed intentions (i.e., prospective memory, PM) entails the allocation of internal and external attention. These processes are crucial for rehearsing PM intentions in memory and for monitoring the presence of the PM cue in the environment, respectively. Aim The study took advantage of the excellent spatial and temporal resolution of magnetoencephalography (MEG) to delineate the neural mechanisms of such memory and monitoring processes underlying PM. Method The spatio-temporal dynamic of theta and alpha oscillations were explored in 21 participants in 2 p.m. tasks and compared respect to a baseline condition (i.e., a lexical decision task with no PM instruction). The PM tasks varied for the load of internally-directed attention (Retrospective-load task) vs externally-directed attention (Monitoring-load task). Results Increase in theta activity was observed in the Retrospective-load task, and was particularly expressed in the regions of the Default Mode Network, such as in medial temporal regions, precuneus, posterior cingulate cortex and medial prefrontal cortex. By contrast, alpha decrease was the most relevant feature of the Monitoring-load task, and it was expressed over bilateral occipital, occipito-parietal and fronto-temporal regions, as well as over left dorsal fronto-parietal regions. Conclusions Theta and alpha oscillations are strictly associated with the direction of attention during the PM tasks. In particular, the theta increase is linked to internal attention necessary for maintaining the intention active in working memory, whereas the alpha decrease supports the external attention for detecting the PM cue in the environment.