Causal evidence for distinct mechanisms of prioritization and suppression in the control of working memory

Abstract

Abstract Working memory requires maintenance of relevant information and suppression of irrelevant information. Our previous study administered rhythmic transcranial magnetic stimulation (TMS) to anterior middle frontal gyrus and inferior intraparietal sulcus and found causal evidence for posterior alpha oscillations and anterior theta oscillation in the control over working memory. However, this previous study did not measure neural oscillations using electrophysiology. To investigate the specific neural mechanism for prioritization and suppression, we conducted a pre-registered four-session experiment with 47 participants that administered rhythmic TMS concurrent with electroencephalography (EEG) as participants performed a retro-cue working memory task. Rhythmic TMS was personalized to the peak frequency of theta and alpha oscillatory activity to increase its efficacy. Our baseline analysis revealed the canonical alpha lateralization pattern in posterior cortex to a retro-cue that indicated which visual hemifield would be tested at probe. Alpha lateralization was positively correlated with the benefit to working memory capacity from the retro-cue. In addition, we found that theta-frequency functional connectivity between the left frontal and parietal cortex increased to the retro-cue. During the stimulation sessions, we found evidence of target engagement such that theta-frequency TMS to frontal cortex and alpha-frequency TMS to parietal cortex successfully increased the amplitude of the targeted oscillation. We replicated our previous behavioral interaction between site and frequency such that rhythmic TMS improved working memory capacity when matched to endogenous activity. Finally, alpha-frequency TMS increased posterior alpha lateralization and theta-frequency TMS increased frontal-parietal theta-connectivity. Altogether, these results provide causal evidence for a model in which alpha lateralization supports suppression and frontal-parietal theta-connectivity supports prioritization. Keywords: Working memory, Rhythmic TMS, Concurrent TMS-EEG, Functional Connectivity