Methods to monitor consciousness
Provided are methods to measure and or monitor consciousness in a subject, including analyzing brain activity with weighted symbolic mutual information (wSMI) and/or Kolgomorov symbolic complexity (KSC). In addition, methods and apparatus to administer a stimulus and/or a medicament to a subject according to their consciousness level which has been determined using the method described herein are also provided.
1. A method to measure or monitor consciousness in a subject and to automatically administer a stimulus or medicament comprising the steps:
a) Acquisition of brain activity signals;
b) Pre-processing of the brain activity signals of step a);
c) Symbolic transformation of the signals from step b) into a series of discrete symbols;
d) Analysis of the series of symbols from step c) using at least weighted symbolic mutual information (wSMI), using the formula:
wSMI
=
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Y
w
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p
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where x and y are all symbols present in signals from electrodes X and Y respectively; p(x,y) is a joint probability of co-occurrence of symbol x in electrode X and symbol y in electrode Y; and p(x) and p(y) are probabilities of those symbols in each respective signal and w(x,y) is a weight matrix;
e) Calculation of a consciousness index based upon the outcome of the analysis of step d), said consciousness index being equal to the weighted symbolic mutual information (wSMI) obtained from the electrodes X and Y;
f) Automatic administration of a stimulus or medicament to the subject based on the value of the consciousness index, said stimulus or medicament including sensory stimulus, pharmacological and/or electromagnetic stimulation.
2. The method according to claim 1 , wherein said brain activity is recorded using a technique selected from the group comprising: electroencephalography (EEG), Magneto-encephalography (MEG), electro-corticography (ECOG), intracranial local field potentials (LFPs), functional magnetic resonance imaging (fMRI) and functional near-infrared imaging (fNIRS).
3. The method according to claim 2 , wherein said brain activity is measured using EEG at least two electrodes and a reference.
4. The method according to claim 1 , wherein the recorded brain activity undergoes pre-processing.
5. The method according to claim 1 , wherein at least one further analysis of brain activity is performed selected from the group comprising:
Mid-latency auditory potential corresponding to the first sound (P1); Contingent Negative Variation (CNV); P300a; P300b; Mismatch negativity (ΔMMN); Contrasted P3b (ΔP300b) and Contrasted P300a (ΔP300a); Multivariate pattern analysis of the mismatch negativity and the P300; Spectral analysis; Power spectrum centroids (MSF, SEF); Spectral entropy (SE); Permutation entropy; Kolgomorov symbolic complexity (KSC); Kolmogorov Chaitin complexity; Phase Locking Value (PLV); Phase Lag Index (PLI); Global algorithmic complexity (GK).
6. The method according to claim 1 , wherein a consciousness index or combined consciousness index is produced based upon the analysis or the combination of analysis of brain activity.
7. The method according to claim 1 , wherein the stimulus or medicament is administered to the subject based on the value of the consciousness index when the consciousness reaches a critical value or target window as shown by electrophysiological markers.
8. The method according to claim 1 , wherein the administration of the stimulus or medicament to the subject based on the value of the consciousness index is electromagnetic stimulation.