Electroencephalography Correlates of Spatial Working Memory Deficits in Attention-Deficit/Hyperactivity Disorder: Vigilance, Encoding, and Maintenance

Abstract

In the current study we sought to dissociate the component processes of working memory (WM) (vigilance, encoding and maintenance) that may be differentially impaired in attention-deficit/ hyperactivity disorder (ADHD). We collected electroencephalographic (EEG) data from 52 children with ADHD and 47 typically developing (TD) children, ages 7-14 years, while they performed a spatial Sternberg working memory task. We used independent component analysis and time-frequency analysis to identify midoccipital alpha (8 -12 Hz) to evaluate encoding processes and frontal midline theta (4 -7 Hz) to evaluate maintenance processes. We tested for effects of task difficulty and cue processing to evaluate vigilance. Children with ADHD showed attenuated alpha band event-related desynchronization (ERD) during encoding. This effect was more pronounced when task difficulty was low (consistent with impaired vigilance) and was predictive of memory task performance and symptom severity. Correlated with alpha ERD during encoding were alpha power increases during the maintenance period (relative to baseline), suggesting a compensatory effort. Consistent with this interpretation, midfrontal theta power increases during maintenance were stronger in ADHD and in high-load memory conditions. Furthermore, children with ADHD exhibited a maturational lag in development of posterior alpha power whereas age-related changes in frontal theta power deviated from the TD pattern. Last, subjects with ADHD showed age-independent attenuation of evoked responses to warning cues, suggesting low vigilance. Combined, these three EEG measures predicted diagnosis with 70% accuracy. We conclude that the interplay of impaired vigilance and encoding in ADHD may compromise maintenance and lead to impaired WM performance in this group.

Frontoparietal neurostimulation modulates working memory training benefits and oscillatory synchronization

“…Importantly, post-training there was a cluster of posterior electrodes that showed significantly greater alpha power for the Sham group compared to the Active group ( p < 0.05); see Figure 5D. Because posterior alpha power increases with WM load (Jensen, et al, 2002; Lenartowicz, et al, 2014; Sauseng, et al, 2009), these results suggest that after training the Active group more efficiently maintained items in WM (Figure 6). …”

Endophenotype best practices

“…The nogo-N2 is considered a candidate endophenotype for alcoholism (Kamarajan & Porjesz, 2015), and similar types of experimental manipulations are likely to inform us about the nature of individual differences in this putative endophenotype. Lenartowicz and colleagues (Lenartowicz et al, 2014) used a visual-spatial version of the Sternberg working memory test in a sample of children with ADHD and typically developing controls to parametrically vary task load and thereby try to isolate the source of the difficulties experienced by children with ADHD. Studies such as these can help to isolate the psychological and neural processes reflected in putative endophenotypes for ADHD such as the P2 ERP component and thus the precise nature of genetic risk reflected in the endophenotype.…”

Oscillations in the human brain during walking execution, imagination and observation

“…Namely, it was demonstrated that the power of EEG alpha oscillation increased during the early and late phases of creative ideas generation [16]. Alpha band oscillations play an active role in attention and working memory [17,18]. Recent studies using treadmill workstations have demonstrated benefits of walking on performance and cognitive abilities that are necessary for tasks requiring attention and memory [19,20].…”