The relationship between alpha burst activity and the default mode network.

Alpha rhythm, described by Hans Berger, is mainly recorded from the occipital cortex (OCC) of relaxed subjects with their eyes closed.Early studies indicated the thalamo‑cortical circuit as the origin of alpha rhythm. Recent works suggest an additional relationship between alpha rhythm and the Default Mode Network (DMN). We simultaneously recorded electroencephalography (EEG) and functional magnetic resonance imaging (fMRI) signals in 36 young males asked to alternately close and open their eyes in 30‑s blocks. Using an EEG source channel montage (the recorded signal was interpolated to designated source positions corresponding to certain brain regions) we found an alpha rhythm sub‑activity composed of its intrinsic events, called alpha bursting segments (ABS). More ABS were observed on source channels related to the DMN than those located over the OCC. Similarly, both the beamformer source analysis and fMRI indicated that the specific ABS activity detected on the posterior cingulate cortex/precuneus (PCC) source channel was less related to the OCC than to the DMN source channels. The fMRI analysis performed using the PCC‑ABS as a general linear model regressor indicated an increased blood oxygenation level‑dependent signal change in DMN nodes - precuneus and prefrontal cortex. These results confirm the OCC source of alpha activity a nd additional specific sources of ABS in the DMN.