PMC

The temporal power spectral density, PSD_T, in this human ECoG tends to a power-law distribution, 1/f^e, with exponent e ~ 3±.25 in slow-wave sleep and e ~ 2±.25 in the awake state (). Spectral peaks of excess power in the clinically significant bands (here gamma and low theta) during arousal and task performance. Adapted from ().

A. Left lateral view of the locations of the MEG sensors (green squares) in relation to the pial surface of the cerebral cortex. The representation for the cortex was reconstructed from MR images. B. Histogram of MEG sensor distances to the nearest point on the pial surface. C. Left lateral view of the locations of EEG electrodes (yellow dots) relative to the cortex. D. Histogram of EEG electrode distances to the pial surface

(Left) Independent Components Analysis of “passive” resting-state fMRI scans shows spatially coherent activity in the posterior cingulate cortex, precuneus and medial prefrontal cortex nodes of the default mode network. (Right) Transient fMRI signal reductions are revealed during an auditory “oddball” attention task in these same regions. Unpublished data (Menon).

The raster plot shows the CAPD from the scalp EEG of a human volunteer at rest with eyes closed. The array was 1-D across the occipital lobe from right to left in steps of 3 mm (total length: 189 mm). Pass band = 12-30 Hz; spacing = 3 mm. CAPD were calculated at the digitizing step Δt = 5 ms and aligned in rows parallel to the left abscissa. The flat areas show the stationarity of the phase within frames. The spikes aligned in rows parallel to the right abscissa show the spatial coordination of the phase discontinuities, often across both hemispheres ().

The relationships are shown between analytic amplitude (smooth curves) and phase differences (spikes) in the beta range in non-invasive EEG (A), MEG gradiometers (B) and MEG magnetometers (C). The horizontal bars indicate the segments when the analytic phase difference was below 0.1 for at least 10 msec, suggesting the presence of CAPD. The large amplitude peak in MEG magnetometer data is an artifact due to cardiac magnetic field. D. The orientations of dipoles are schematized with respect to gyri and sulci in widely synchronized oscillatory potentials in the beta and gamma ranges for EEG (vertical arrows) and MEG (horizontal arrows). The signals from tangential source components (blue or black arrows) on opposite walls of sulci tend to cancel; this could explain why CAPD were not observed in the MEG recording.