The level of consciousness of patients identified by EEG during speech perception

Scientists have proposed a new method of determining the level of consciousness of patients with disorders of consciousness — in potentials in the electroencephalogram (EEG) during speech perception. In healthy people, the bursts of activity were observed in the perception of both words and whole phrases and sentences, and in patients with impaired consciousness the EEG was only a trace of perception of individual words. The researchers trained a linear classifier based on different characteristics of the EEG during speech perception to distribute patients according to diagnoses and to predict the improvement in their condition. The algorithm coped with the task with a high level of accuracy, and his predictions come true more often than in the analysis of standard behavioral tests. Article published in the journal Nature Neuroscience.

In patients with traumatic brain injuries there are different degrees of impairment of consciousness, from coma to unresponsive wakefulness syndrome (vegetative state) and apallic syndrome (awake coma). The boundary between these States is thin, and the doctors often put the wrong diagnosis. One approach to assessing the level of consciousness on dynamic characteristics of neural activity in the electroencephalogram (EEG) and functional magnetic resonance imaging (fMRI).

Scientists from China and France under the leadership of Wang Liping (Liping Wang) of the Chinese Academy of Sciences was looking for a correlation between activity in the EEG that occurs during speech perception at the level of individual words, phrases, or whole sentences, and level of consciousness. EEG was recorded in 47 healthy volunteers, 42 patients with apallic syndrome and 36 — syndrome unresponsive wakefulness. The participants listened to the recording, consisting of monosyllabic words, which sounded in every 250 milliseconds. At a basic lexical level, it was individual words, in the complicated version — phrase of two words, and finally sentences of four words. The EEG was looking for phase coherence between attempts — bursts of electrical activity in the brain, which coincided with a frequency of four Hertz (when participants listened to words), two Hertz (for phrases) or one Hertz (for suggestions).

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