EEG Features of Working Memory Impairment in Alzheimer’s Dementia and Mild Cognitive Impairment

The presence of working memory impairments in individuals with Alzheimer’s Dementia (AD) or Mild Cognitive Impairment (MCI) is well-accepted; however, the neurophysiological mechanisms contributing to these impairments have not been fully elucidated. Research has reliably shown that oscillatory activity, driven by repetitive and synchronous activity within and between neuronal populations, plays a significant role in memory functioning and can be accurately captured using electroencephalography (EEG). While resting-state studies have identified aberrant oscillatory activity, mainly in those with AD, there is a paucity of research investigating how EEG activity behaves during cognitive processing. As such, the overall objective of this study was to assess the relationship between oscillatory activity and working memory impairments in AD and MCI, with a focus on three EEG features: theta and alpha power, theta-gamma coupling, and theta phase synchronization. We hypothesized that these EEG features would be most impaired in those with AD, while individuals with MCI would present with less significant impairments. Additionally, we hypothesized that each of these features would be associated with working memory performance. In the first study, we found that the AD group demonstrated the smallest increase in theta power following the onset of the 2-back stimulus; while compared to controls, the MCI group demonstrated a smaller increase in theta power on the most difficult 3-back condition. Similarly, in the second study, the AD group demonstrated the lowest level of theta-gamma coupling followed by MCI and HC groups. Finally in the third study, we found that the AD group demonstrated impaired theta phase synchronization between the temporal region and the rest of the brain, while no differences were found between the HC and MCI groups. Our results also demonstrated that each of the EEG features were associated with working memory performance to varying degrees. Taken together, findings from these studies revealed widespread impairments in EEG activity in AD, along with an intermediate and inconsistent level of impairment in those with MCI. Ultimately, this research advances our understanding of the neurophysiological mechanisms underlying working memory impairments in MCI and AD and may help guide the development of novel interventions in the future.Ph.D