Theta-Gamma Coupling and Working Memory in Alzheimer's Dementia and Mild Cognitive Impairment

• Published in: Frontiers in aging neuroscience 2018-04, Vol.10, p.101-101
• Main Authors: Goodman, Michelle S, Kumar, Sanjeev, Zomorrodi, Reza, Ghazala, Zaid, Cheam, Amay S M, Barr, Mera S, Daskalakis, Zafiris J, Blumberger, Daniel M, Fischer, Corinne, Flint, Alastair, Mah, Linda, Herrmann, Nathan, Bowie, Christopher R, Mulsant, Benoit H, Rajji, Tarek K
• Format: Article
• Language: English
• Subjects: Addictions; Age; Alzheimer's disease; Alzheimer’s dementia; Brain research; Cognitive ability; Dementia; Dementia disorders; EEG; electroencephalography; Health sciences; Memory; Mental health; Mental task performance; mild cognitive impairment; neural oscillations; Neuroscience; Short term memory; Theta rhythms; theta-gamma coupling; working memory
• ISSN: 1663-4365; 1663-4365
• DOI: 10.3389/fnagi.2018.00101

Working memory deficits are common among individuals with Alzheimer's dementia (AD) or mild cognitive impairment (MCI). Yet, little is known about the mechanisms underlying these deficits. Theta-gamma coupling-the modulation of high-frequency gamma oscillations by low-frequency theta oscillations-is a neurophysiologic process underlying working memory. We assessed the relationship between theta-gamma coupling and working memory deficits in AD and MCI. We hypothesized that: (1) individuals with AD would display the most significant working memory impairments followed by MCI and finally healthy control (HC) participants; and (2) there would be a significant association between working memory performance and theta-gamma coupling across all participants. Ninety-eight participants completed the N-back working memory task during an electroencephalography (EEG) recording: 33 with AD (mean ± SD age: 76.5 ± 6.2), 34 with MCI (mean ± SD age: 74.8 ± 5.9) and 31 HCs (mean ± SD age: 73.5 ± 5.2). AD participants performed significantly worse than control and MCI participants on the 1- and 2-back conditions. Regarding theta-gamma coupling, AD participants demonstrated the lowest level of coupling followed by the MCI and finally control participants on the 2-back condition. Finally, a linear regression analysis demonstrated that theta-gamma coupling ( = 0.69, < 0.001) was the most significant predictor of 2-back performance. Our results provide evidence for a relationship between altered theta-gamma coupling and working memory deficits in individuals with AD and MCI. They also provide insight into a potential mechanism underlying working memory impairments in these individuals.