Figure 1.
Stability of wakefulness under MV and SB indexed by EEG.
(A). Scalp voltage topographies of alpha power (up) and theta (bottom) averaged across the 4 EEG-fMRI sessions reveal a typical pattern of wakefulness characterized by a high posterior alpha power and a low anterior mid-frontal power. (B). Dynamics of the (posterior alpha power)/(mid-frontal theta power) ration is plotted across time for the 4 EEG-fMRI sessions. This index of wakefulness was stable across the 4 sessions, and confirmed a stable level of wakefulness all along the fMRI experiments, with no difference between SB and MV.
Figure 2.
Restoration of DMN under mechanical ventilation.
(A). Comparison of BOLD signal between MV and SB revealed a specific increase of activation in the default-mode network associated in awake controls in introspection and self-consciousness. No significant result was observed in the opposite contrast. See Table 1 for detailed fMRI results. (B&C). Functional connectivity assessed with a hypothesis-driven approach revealed a larger correlation with precuneus activity in posterior mesial areas during MV than during SB (B), and a larger correlation between brainstem activity and a large anterior cortico-subcortical network during SB than during MV (C). This large network resembles the executive attention network.
Table 1.
Synthesis of fMRI results.
Figure 3.
Functional MR connectivity assessed with an ICA method.
(A).Default mode network (DMN): bilateral medial prefrontal and anterior cingulate cortices (1), bilateral precuneus (2), bilateral superior parietal cortices (3). (B).Mean values ± standard deviation of DMN integrations for the mechanical (MV) and the spontaneous (SB) breathing blocks of resting state. The asterisk indicates a significant difference between conditions. (C). Sensorimotor network (SMN): bilateral supplementary motor area (1) and bilateral sensorimotor cortices (2). (D).Mean values ± standard deviation of SMN integrations for the mechanical (MV) and the spontaneous (SB) breathing blocks of resting state. NS = non-significant difference between conditions; AU = arbitrary unit.