PMC4840417_01
EEG analysis. A) High-resolution EEG (82 electrodes) recording of onset of a 3-Hz SW burst, using average (left) and Laplacian (right) references. Topographic maps of an average spike at peak and half-peak amplitudes are shown. Vertical dotted lines signal 1-s intervals. Vertical scale is 1 mV (left) and 160 muV/cm2 (right). B) EEG sample of phase II sleep, with well-formed and symmetrical spindles. C) Spectra of alpha (left) and spindles (right) for the left and right hemisphere, highlighting the symmetrical features. D) Somatic-sensory evoked potentials to stimulation of the median nerve. The N20 and P25 potentials of each hemisphere to stimulation of the contralateral peripheral nerve are overlapped both for the C3/4 and CP3/4 electrode positions on the scalp. Vertical scale: 2.5 muV, horizontal scale: 20 ms.
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The EEG revealed normal background activity, with bursts of high amplitude SWD at 3 Hz, maximum over anterior head electrodes and an odd asymmetry: high amplitude paroxysms were clearly seen over the left hemisphere while they had a smaller amplitude over the right hemisphere (Fig. 1A). No paroxysmal activity was evoked by intermittent photic stimulation, and sleep was well-structured, with symmetrical spindles, vertex waves, and K-complexes (Fig. 1B). Spectral analysis of EEG signal with a focus on the alpha band was carried out using standard fast Fourier transform (FFT) on a 10-second epoch of wakefulness with eyes closed (Fig. 1C, left), while for spindles, N = 40 epochs of 1 s were used (Fig. 1C, right). Additionally, a 2-hour high-resolution EEG recording was performed using 82 scalp electrodes (Fig. 1A). Somatic-sensory evoked potentials (SSEP) were obtained through electrical stimulation of the median nerve in the left and right wrists and computed for each hemisphere at C3/4 and CP3/4 (Fig. 1D).
EEG-fMRI. A) SW burst during EEG-fMRI recording. Dotted vertical lines are 1-second marks; vertical scale: 500 muV. B) BOLD activation (red) and deactivations (blue) associated with the SW burst, coregistered with the anatomical MRI. C) SW-related BOLD overlaid on the inflated cortical surface. Sulci are represented in deep gray, with corresponding z-scores indicated by the color bar.
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MR-compatible EEG system, during which a single burst of 3-Hz SWD with a duration of 15 s was recorded (Fig. 2A). Magnetization-Prepared Rapid Gradient-Echo (MP-RAGE) images were collected for anatomical reference.
Dynamics of average independent components (ICs) resulting from decomposition of the SW recorded during simultaneous EEG-fMRI, classified in spike (S) and wave (W) events. A) IC time courses and classification in spike (S) and wave (W). B) Topographic maps and representation of the sLORETA source analysis results (threshold at 50%) with a dipole at point of maximum score (green), for the spike (left) and wave (right) ICs. C) Correlation analysis, represented in the flattened cortex of the left hemisphere, for the spike (left) and wave (right) IC sources. Arrows point to the direction of lag, and the strength of the association is represented by the color scale. The BOLD scale is in z-score. RACi : rostral anterior cingulate; POr : pars orbicularis; PT : pars transverse; IPC : inferior parietal cortex; MT : medial temporal; PCu : precuneus. Flattened cortex orientation is indicated by P (posterior), V (ventral), R (rostral), and A (anterior).
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Components with nondipolar fields and time courses compatible with artifacts were visually excluded, yielding 16 remaining ICs (Fig. 3A). Segments representing the SWD were then averaged, and the components with larger amplitude were visually classified into spikes (S) and waves (W) (Fig. 3B).
PMC4840417_02
GABA NMR Spectra. Voxel positions for the occipital cortex and thalamus of both hemispheres and corresponding edited GABA spectra for the patient. The estimated areas of the GABA peak relative to the water and Cr reference peaks are shown on the left side of each spectrum. Comparable results were obtained in the two occipital regions with a ratio for the left/right areas of 1.01 (GABA/H20) and 1.09 (GABA/Cr). The thalamic spectra suggest a larger GABA concentration in the left thalamus with ratios of 1.61 (GABA/H20) and 2.57 (GABA/Cr).
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Four data sets, with the 25 x 20 x 30-mm3 voxel successively placed on the left (right) thalamus and on the left (right) occipital cortex (Fig. 4) were acquired.