Disentangling conscious from unconscious cognitive processing with event-related EEG potentials

Area of Science:

• Cognitive Neuroscience
• Clinical Neurophysiology

Background:

• Cognitive neuroscience research has expanded the understanding of unconscious cognitive processing.
• New clinical approaches aim to differentiate conscious from unconscious cognitive functions in non-communicating brain-injured patients.

Purpose of the Study:

• To review recent advancements in probing conscious and unconscious cognitive processing in brain-injured patients.
• To illustrate the use of electroencephalography (EEG) markers for diagnosing and predicting outcomes in disorders of consciousness.

Main Methods:

• Focus on EEG signals recorded at the bedside in response to auditory stimuli (sounds and words).
• Identification of specific EEG markers differentiating unconscious (Mismatch Negativity - MMN, N400) from conscious (P3b, Late Positive Component - LPC/P600) processing.

Main Results:

• Conscious processing of auditory regularity and semantic content shares a neural signature (P3b, P600/LPC).
• Unconscious processing is associated with an earlier neural signature (MMN, N400).
• These markers can be measured at the bedside.

Conclusions:

• A two-stage serial model of processing is proposed, distinguishing unconscious and conscious signatures.
• Bedside EEG measurements provide valuable diagnostic and prognostic information for consciousness recovery.
• A bidirectional approach using healthy subjects and brain-damaged patients is fruitful for understanding cognition and consciousness.