EEG fractal dimensions predict high-level behavioral responses in minimally conscious patients

Abstract

Background: Brain-injured patients may enter a state of minimal or inconsistent awareness termed Minimally Conscious State (MCS). Such patient may (MCS+) or may not (MCS-) exhibit high-level behavioral responses, and the two groups retain two inherently different rehabilitative paths and expected outcomes. We hypothesized that brain complexity may be treated as a proxy of high-level cognition and thus could be used as a neural correlate of consciousness. Methods: In this prospective observational study, 68 MCS patients (MCS-: 30; women: 31) were included (median [IQR] age 69 [20]; time post-onset 83 [28]). At admission to intensive rehabilitation, 30 minutes resting-state closed-eyes recordings were performed together with consciousness diagnosis following international guidelines. The width of the Multifractal Singularity Spectrum (MSS) was computed for each channel time series and entered nested cross-validated interpretable Machine Learning (ML) models targeting the differential diagnosis of MCS+/-. Results: Frontal MSS widths (p < 0.05), as well as the ones deriving from the left centro-temporal network (C3: p = 0.018, T3: p = 0.017; T5: p = 0.003) were found to be significantly higher in the MCS+ cohort. The best performing solution was found to be the K-Nearest Neighbor model with an aggregated test accuracy of 75.5% (median [IQR] AuROC for 100 executions 0.88 [0.02]). Coherently, the electrodes with highest Shapley values were found to be Fz and Cz, with four out the first five ranked features belonging to the fronto-central network. Conclusion: MCS+ is a frequent condition associated with a notably better prognosis than the MCS-. High fractality in the left centro-temporal network results coherent with neurological networks involved in the language function, proper of MCS+ patients. Using EEG-based interpretable algorithm to complement differential diagnosis of consciousness may improve rehabilitation pathways and communications with caregivers.