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    • SB 525334 cost Fig shows the whole scalp distribution

    2018-10-29

    Fig. 2 shows the whole scalp distribution of VLFO power. At REST both groups showed maximal power along the frontal pole and midline regions. During WORK the VLFO power was lower for both groups although it remained greatest in the frontal pole and centro-parietal areas. Within the ADHD group the C-WAIT and F-WAIT VLFO signature was more similar to REST than WORK despite some evidence of focal reductions in frontal areas and temporo-parietal junction and a degree of exacerbation in temporal and centroparietal locations. In contrast, in the control group the VLFO signature during C- and F-WAIT was similar to that during WORK with suppression of EEG power across the whole scalp. As predicted, sLORETA localized the resting VLFO for both groups to midline structures, including key DMN regions such as medial frontal gyrus (BA 6 & 8) and precuneus (BA 31) (see AppendixFig. A.1). Fig. 3 shows the intracranial source localization for the SB 525334 cost between REST and non-REST conditions. In line with the scalp distribution, sLORETA identified significant WORK and F-WAIT induced attenuations within the control group in the medial frontal gyrus (BA 6), precentral and postcentral gyrus (BA 4), as well as paracentral lobule (BA 6) (REST vs. WORK: pseudo t=7.48, corrected p=0.03; REST vs. F-WAIT, pseudo t=7.14, corrected p=0.03). For controls the REST to C-WAIT effect failed to reach significance after stringent control for multiple testing (pseudo t=6.76, corrected p=0.07), albeit the attenuations were localized to similar regions. The ADHD group displayed REST-to-WORK attenuation in similar regions but the effects were smaller and failed to reach significance (pseudo t=7.49, corrected p=0.09). Nominally significant REST to C- and F-WAIT reductions occurred in DMN-related regions, including precuneus, superior parietal lobule, postcentral gyrus and medial frontal gyrus (F-WAIT: pseudo t=5.07, corrected p=0.20; C-WAIT: pseudo t=6.16, corrected p=0.15) but these were not significant when p values were adjusted for multiple testing. Consistent with the scalp maps, within the ADHD group the VLFO activity was increased during the F-WAIT and C-WAIT compared to REST within the temporal regions including limbic lobe and insula (blue regions on Fig. 3). For the REST-to-F-WAIT contrast there was a significant group difference in insula (BA 13) and inferior frontal gyrus (pseudo t=3.65, corrected p=0.035). For the REST-to-C-WAIT contrast a significant group difference was identified in insula, middle and superior temporal gyrus (BA 13, 21, 22, 41; pseudo t=3.67, corrected p=0.01). There was no group difference in terms of the REST-to-WORK transition (p=.42). To explore these unpredicted temporal lobe/insula effects further, we then extracted the sLORETA generators within the local regions showing group difference when waiting and examined their correlations with the delay aversion and discounting scores on QDQ. There were highly significant positive correlations between QDQ scores and F-WAIT activity in insula (MNI[x/y/z]=−35/20/5; rdelay aversion=.57, p<0.001; rtemporal discounting=.57, p<.001) and inferior frontal gyrus (MNI[x/y/z]=−35/25/0; rdelay aversion=.51, p=0.001; rtemporal discounting=.53, p<.001); and C-WAIT activity in superior temporal gyrus (MNI[x/y/z]=50/−20/5; rdelay aversion=.46, p <0.01; rtemporal discounting=.42, p<01), middle temporal gyrus (MNI[x/y/z]=60/−30/−5; rdelay aversion=.41, p<0.01; rtemporal discounting=.37, p<05) and insula (MNI[x/y/z]=45/−15/5; rdelay aversion=.53, p=0.001; rtemporal discounting=.50, p=001).
    Discussion First, we replicated prior evidence of suppression of VLFO activity during episodes of waiting and working relative to resting in healthy children and adolescents (Hsu et al., 2013). Our study supports the view that in terms of spontaneous brain activity, waiting, despite some characteristics in common with resting, is similar to other goal-directed activities such as performing information processing tasks. Prior debates about the functional status of EEG-VLFO as a measure of real neuronal activity, and the extent to which it is functionally similar to BOLD oscillations (Demanuele et al., 2013; Vanhatalo et al., 2005), notwithstanding, the localization of sources to midline structures in the current study raises new questions about the relationship between the EEG-VLFO network and the DMN. Indeed recent studies using simultaneous EEG-fMRI recordings have identified a direct association between spontaneous BOLD signals and EEG in both infra-slow (Hiltunen et al., 2014) and higher frequency domains (Laufs et al., 2003; Mantini et al., 2007). There has also been evidence indicating an association between the increase of theta power (particularly in anterior mPFC) and Rest-to-Work BOLD signal attenuation in the DMN during cognitive task performance (Meltzer et al., 2007; Scheeringa et al., 2009). Further work should examine the functional significance of EEG-VLFO by co-registering EEG signals to structural images attained from MRI or using simultaneous fMRI-EEG recordings. Also, it is important to investigate the effect of attenuation of EEG power from resting to waiting in different frequency, including traditional frequency bands.