Neurochemical dynamics during two hypnotic states evidenced by magnetic resonance spectroscopy

Figures

• 

  Fig. 1. Illustration of experimental setup. Participants were randomly allocated to two different experimental sequences to counterbalance sequential effects. Both sequences were identical except that for sequence 1, the control conditions (CS1, CS2) were performed first, followed by the hypnosis induction and deepening. In sequence 2, the order was reversed. During all MRS measurements, heart rate and respiration data were recorded. In both sequences, a post-MR questionnaire was given to the participants to evaluate the comparability of the states compared to when under familiar circumstances. Furthermore, the questionnaire also assessed stability of the states during the measurements, tiredness of the participants during the measurements and applied effort to maintain the states (including wakeful state during control conditions).

• 

  Fig. 2. Illustration of the MRS study’s voxel definition and placements. Shown are six images depicting (a) PO and (b) pSTG region in sagittal and coronal orientation. The images in the top row are from the fMRI study and show the significant area (PO region) when comparing hypnotic (HS1, HS2) with control states (CS1, CS2) on group-level. The statistical thresholds set for illustrational purposes were height threshold of p < 0.001 (FWE) with an extended threshold k = 10 voxels for PO. The thresholds for the pSTG-region were height threshold of p < 0.001 uncorrected with extent threshold k = 10. The images in the middle row portray the manually positioning of the MRS voxels from a single participant based on the landmarks provided by the fMRI-study. The last row shows the voxel positioning overlaps of all participants in the MNI-space. The level of overlap is colour coded with the percent overlap indicated in the colour bar ranging from 0 (0%) to 1 (100%). Note that the illustrations are shown according to the radiological convention.

• 

  Fig. 3. Exemplary spectra from PO and pSTG fitted with LCModel. Fitted spectra (red) are superimposed with the raw spectrum (grey). Differences of fit and raw signals (residuum) are shown at the figure top. Spectra of the fitted substances are displayed below raw and fit.

• 

  Fig. 4. Illustration of overlays of all analyzed spectra for each condition and region. All spectra are depicted in grey, the black spectra indicate the average spectra.

• 

  Fig. 5. Raincloud plots illustrating the tmI concentrations for the four conditions. The plots consist of a density plot for visualization of the distribution, supplemented by visualization of the mean (large dot) and 95% confidence interval (indicated by lines above and below the dot), and boxplot surrounded by scattered individual data points. Post-hoc comparisons revealed significantly higher tmI concentrations in the deeper hypnosis state (HS2) compared to its control condition (CS2) and to the less deep hypnotic state (HS1).