Theta and Alpha Alterations in Amnestic Mild Cognitive Impairment in Semantic Go/NoGo Tasks

Abstract

Growing evidence suggests that cognitive control processes are impaired in amnestic mild cognitive impairment (aMCI); however the nature of these alterations needs further examination. The current study examined differences in electroencephalographic theta and alpha power related to cognitive control processes involving response execution and response inhibition in 22 individuals with aMCI and 22 age-, sex-, and education-matched cognitively normal controls. Two Go/NoGo tasks involving semantic categorization were used. In the basic categorization task, Go/NoGo responses were made based on exemplars of a single car (Go) and a single dog (NoGo). In the superordinate categorization task, responses were made based on multiple exemplars of objects (Go) and animals (NoGo). Behavioral data showed that the aMCI group had more false alarms during the NoGo trials compared to controls. The EEG data revealed between group differences related to response type in theta (4-7 Hz) and low-frequency alpha (8-10 Hz) power. In particular, the aMCI group differed from controls in theta power during the NoGo trials at frontal and parietal electrodes, and in low-frequency alpha power during Go trials at parietal electrodes. These results suggest that alterations in theta power converge with behavioral deterioration in response inhibition, whereas alterations in low-frequency alpha power appear to precede behavioral changes in response execution. Both behavioral and electrophysiological correlates combined provide a more comprehensive characterization of cognitive control deficits in aMCI.

Keywords: Go/NoGo; alpha; categorization; cognitive control; mild cognitive impairment; response execution; response inhibition; theta.

Figure 1

Group comparison of spectrograms for response types across electrode clusters. The spectrograms for the Controls and aMCI groups across Go and NoGo trials at the three electrode clusters (Frontal/Central/Parietal) are represented. The zero millisecond (ms) time point (dashed black line) represents the Go or NoGo stimulus onset. Theta (4–7 Hz), low-frequency alpha (8–10 Hz), and high-frequency alpha (11–13 Hz) power were computed between zero ms (dashed black line) and 600 ms (solid magenta line).

Figure 2

Group comparison of mean power for response types across electrode clusters. The bar graphs represent mean power in the theta (4–7 Hz), low-frequency alpha (8–10 Hz), and high-frequency alpha (11–13 Hz) bands for Go and NoGo trials in the Controls and aMCI groups at the three electrode clusters (Frontal/Central/Parietal). Error bars represent standard error. ^*p < 0.05, ^**p < 0.01.