Content-Free Awareness: EEG-fcMRI Correlates of Consciousness as Such in an Expert Meditator - PubMed (original) (raw)

Content-Free Awareness: EEG-fcMRI Correlates of Consciousness as Such in an Expert Meditator

Ulf Winter et al. Front Psychol. 2020.

Abstract

The minimal neural correlate of the conscious state, regardless of the neural activity correlated with the ever-changing contents of experience, has still not been identified. Different attempts have been made, mainly by comparing the normal waking state to seemingly unconscious states, such as deep sleep or general anesthesia. A more direct approach would be the neuroscientific investigation of conscious states that are experienced as free of any specific phenomenal content. Here we present serendipitous data on content-free awareness (CFA) during an EEG-fMRI assessment reported by an extraordinarily qualified meditator with over 50,000 h of practice. We focused on two specific cortical networks related to external and internal awareness, i.e., the dorsal attention network (DAN) and the default mode network (DMN), to explore the neural correlates of this experience. The combination of high-resolution EEG and ultrafast fMRI enabled us to analyze the dynamic aspects of fMRI connectivity informed by EEG power analysis. The neural correlates of CFA were characterized by a sharp decrease in alpha power and an increase in theta power as well as increases in functional connectivity in the DAN and decreases in the posterior DMN. We interpret these findings as correlates of a top-down-initiated attentional state excluding external sensory stimuli and internal mentation from conscious experience. We conclude that the investigation of states of CFA could provide valuable input for new methodological and conceptual approaches in the search for the minimal neural correlate of consciousness.

Keywords: EEG-fMRI; consciousness as such; content-free awareness (CFA); default-mode network (DMN); disconnected consciousness; dorsal attention network (DAN); meditation; neural correlate of consciousness (NCC).

Copyright © 2020 Winter, LeVan, Borghardt, Akin, Wittmann, Leyens and Schmidt.

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Figures

FIGURE 1

FIGURE 1

The maps of the two ICA components representing DMN and DAN that have been used in the functional connectivity analysis. The maps are shown in axial and sagittal views superimposed on a standard MNI152 T1 2 mm resolution brain template. The following areas are visible: DMN: posterior cingulate cortex (with the adjacent regions of the precuneus), left and right inferior parietal lobule and medial prefrontal cortex; DAN: left and right intraparietal sulcus, left and right frontal eye field.

FIGURE 2

FIGURE 2

ECG and breathing measures. The color bars represent the median values of the 5-min epochs of rest (blue), content-related meditation (yellow) and content-free awareness (pink) in each case. From left to right: heart rate (HR), heart-rate variability (HRV, RMSSD = root mean square of successive differences), breathing rate (BR), estimated oxygen consumption (OCe).

FIGURE 3

FIGURE 3

Topographies of EEG spectral power. Upper row rest condition, lower row difference between content-free awareness (CFA) and rest. Increases in power are displayed in red, decreases in blue. Black dots denote the electrodes of the extended 10–20 system.

FIGURE 4

FIGURE 4

EEG spectral power during rest, content-related meditation and content-free awareness. For each frequency band, the electrodes with the most significant differences for the main contrast (content-free awareness vs. rest) are shown (theta band: F6, F7, and Pz; alpha band: FCz, P7, and P8). The significance values for the different contrasts are given in Table 2. The color bars represent the median values of spectral power (μV2) of the 5-min epochs of rest (blue), content-related meditation (yellow) and content-free awareness (pink) in each case.

FIGURE 5

FIGURE 5

fMRI connectivity during rest, content-related meditation and content-free awareness. For each network, only the pairs of nodes with the most significant differences for the main contrast (content-free awareness vs. rest) are shown. A complete list of all significant differences is given in Table 3. The color bars represent the median values of Fisher-transformed correlation coefficients of the 5-min epochs of rest (blue), content-related meditation (yellow) and content-free awareness (pink) in each case. DMN = default mode network, DAN = dorsal attention network, PAC = primary auditory cortex, PCC = posterior cingulate cortex, IPL = inferior parietal lobule, IPS = intraparietal sulcus, FEF = frontal eye field, IFG = inferior frontal gyrus, L = left, R = right.

FIGURE 6

FIGURE 6

Correlations between the time courses of fMRI connectivity and EEG power. Shown are all Pearson’s correlation coefficients of time courses with significant differences for the main contrast (content-free awareness vs. rest). Blue cells display negative correlations red cells display positive ones. Significant correlations (p < 0.05, FDR-corrected) are printed in bold.

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