Brain-state determines learning improvements after transcranial alternating-current stimulation to frontal cortex

Background: Theories of executive control propose that communication between medial frontal cortex (MFC) and lateral prefrontal cortex (IPFC) is critical for learning. 6-Hz phase synchronization may be the mechanism by which neural activity between MFC and IPFC is coordinated into a functional network. Recent evidence suggests that switching from eyes closed to open may induce a change in brain-state reflected by enhanced executive control and related functional connectivity. Objective/Hypothesis: To examine whether causal manipulation of MFC and IPFC can improve learning according to the brain-state induced by switching from eyes closed to open. Methods: Within-subjects, sham-controlled, double-blind study of 30 healthy subjects, each receiving 6Hz in-phase high definition transcranial alternating-current stimulation (HD-tACS) applied to MFC and right IPFC prior to performing a time estimation task. Results: HD tACS with eyes open improved learning ability relative to sham, whereas HD-tACS with eyes closed had no significant effect on behavior. Conclusion: Results suggest a phase-sensitive mechanism in frontal cortex mediates components of learning performance in a state-dependent manner. (C) 2018 Elsevier Inc. All rights reserved.