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While several studies have found that neural oscillations play a key role in the functioning of working memory, the nature of aberrant oscillatory activity underlying working memory impairments in Alzheimer's disease (AD) and mild cognitive impairment (MCI) remains largely unexplored. These individuals often display structural alterations in brain regions and pathways involved in working memory processes and therefore may also display altered oscillatory activity during memory activation. Electroencephalographic (EEG) activity was recorded during the N-back working memory task in three groups: AD (n = 29), MCI (n = 100), and healthy controls (HCs; n = 40). Theta (4-7 Hz) and alpha (7.5-12 Hz) modulation was measured in response to the stimulus presentation during correct and incorrect responses. This modulation represents the change in EEG activity associated with the stimulus onset and was measured as a ratio of post stimulus power to pre stimulus power. We also assessed the relationship between change in oscillatory power and working memory performance. Compared to HCs, the AD group demonstrated the lowest working memory accuracy and a smaller theta ratio for correct responses on the 2-back condition; the MCI group demonstrated a smaller theta ratio for correct responses on the 3-back condition. Finally, we observed that the theta ratio, but not the alpha ratio, was a significant predictor of working memory performance in the three groups for all conditions. Taken together, these behavioral and electrophysiological results suggest that in addition to impairments in working memory performance, modulation of theta, but not alpha power, may be impaired in MCI and AD. [ABSTRACT FROM AUTHOR]

Abstract: Objective: The induction of long interval cortical inhibition (LICI) in motor cortex with paired pulse transcranial magnetic stimulation (ppTMS) is an established paradigm for the assessment of cortical inhibition, proposed to be related to GABAB receptor inhibitory neurotransmission. This study aimed to further evaluate recent methods of the assessment of LICI in non motor regions with ppTMS and electroencephalography (EEG). Methods: ppTMS was applied using a single coil to the motor and dorsolateral prefrontal cortex (DLPFC) in 14 healthy subjects, and in the parietal lobe in 5 of those subjects. Results: In the motor cortex, LICI resulted in significant suppression in mean cortical evoked activity on EEG between 75 and 250ms following delivery of the test stimulus. Maximal inhibition was seen from 50 to 250ms in DLPFC, and between 50 and 175ms in the parietal lobe. Conclusions: ppTMS may be used to produce LICI in several cortical regions with a time course similar to known GABAB activity. Significance: ppTMS induction of LICI can be recorded by combining TMS with EEG and seems to relate to GABAB activity. [Copyright &y& Elsevier]