The proposed research will use closed-loop transcranial magnetic stimulation (TMS) based on individualized brain networks to establish parameters that can reliably control brain states. This will be tested in healthy aging and mild cognitive impairment (MCI) cohorts. The investigators will study network activation and neural oscillatory mechanisms underlying the network that regulates working memory and then target this network using closed-loop TMS to the Prefrontal Cortex. Investigators will measure the impact of TMS on working memory performance and task-based neural activity. The project will use brain stimulation and network modeling techniques to enhance working memory in healthy older adults and MCI and will demonstrate the value of closed-loop, network-guided TMS for future clinical applications.