Gamma Induction Using Transcranial Alternating Current Stimulation in Alzeihmer’s Disease

Abstract

Thanks to technology and advances in the medical field, our population's lifespan continues to lengthen. As a result, aging related neurodegenerative disorders become more prevalent. Manipulating brain oscillations is a potential solution to cognitive impairments that result from these disorders. This form of manipulation can be accomplished with the use of transcranial alternating current stimulation (tACS). The use of noninvasive stimulation technology to explore brain activity provides greater insight into the role brain oscillations have in cognition, specifically, into the role of gamma oscillations in Alzheimer's Disease (AD) patients. AD is characterized by alterations in inflammatory processes and depositions of proteins like Aβ and tau, as well as alterations in levels of gamma. Recent studies have shown that inducing gamma in mice modulates microglial activities and thus modified the inflammatory processes. In this study we researched the safety and feasibility of the first in-human study that translates these findings using tACS at 40Hz to induce gamma oscillations through a 10 day period in AD. Using MRI and PET imaging, we were able to optimize the intervention and target regions with greater Aβ accumulation. Fifteen participants were separated into 3 groups with slightly differing stimulation protocols, they all had daily recordings of changes in EEG, cognition, adverse effects, and safety. Gamma induction was compared pre and post stimulation and the results showed that gamma was induced post-stimulation, as well as the possibility of additive effects throughout stimulations. Additionally, N-back tasks results suggest the protocol was beneficial to cognitive processes with improvements to declarative memory and a reduction in the P200 latency in the N-back task, indicating quicker working memory processing. There was a correlation in declarative memory and gamma connectivity in the bi-hemispheric temporal stimulation which indicates that gamma contributes to an improvement in cognitive performance. Overall, there were no noteworthy adverse effects and minimal levels of attrition.