The 32 million Alzheimer's disease (AD) and 69 million prodromal AD patients worldwide contribute to a large economic burden. Effective and safe therapies that slow or prevent the progression from mild cognitive impairment (MCI) to AD are therefore of high priority. Transcranial alternating current stimulation (tACS) is a safe and patient-friendly non-invasive brain stimulation technique that serves as a potential candidate for reducing and/or slowing cognitive impairment. Application of tACS in the gamma frequency range, specifically around 40 Hz, has been studied in patients with AD and MCI due to AD. In these patients, a single session of 40 Hz tACS at the precuneus showed to improve episodic memory and to increase gamma power, as measured with electroencephalography. These findings will be replicated in the current study in patients with MCI due to AD, using magnetoencephalography (MEG) recorded before, during and after tACS. In this way, brain activity and network changes that underlie this improvement in episodic memory can be studied with greater temporal and spatial detail.