Basic discriminative and semantic processing in patients in the vegetative and minimally conscious state

Area of Science:

• Neuroscience
• Clinical Neurology

Background:

• Disorders of Consciousness (DOC) following brain injury present significant assessment challenges due to lack of reproducible motor responses.
• Event-related potentials (ERPs) via EEG offer a promising avenue for evaluating cognitive function in DOC patients.

Purpose of the Study:

• To investigate the utility of auditory event-related potentials (ERPs) in assessing cognitive function in behaviorally unresponsive or low-responsive DOC patients.
• To evaluate the hierarchical approach for ERP assessment, where higher-order responses are contingent on early responses.

Main Methods:

• Nineteen DOC patients underwent passive auditory stimulation with paradigms targeting Mismatch Negativity (MMN) and N400 (word-pair and sentence contexts).
• ERPs were recorded at two time points to assess responses like MMN, N1, N400, and Late Positive Complex (LPC).

Main Results:

• Most patients (n=15) showed no response to auditory stimulation.
• MMN was identified in 2 patients, N1 in 1 patient (N400 Words paradigm), and LPC in 2 patients (N400 Sentences paradigm).
• LPC responses were observed in patients without MMN, contradicting the proposed hierarchical assessment model.

Conclusions:

• The findings challenge the hierarchical assessment approach for ERPs in DOC patients.
• A minority of DOC patients demonstrated preserved higher information processing, indicated by N400-related components.
• Approximately 10% of the studied DOC patients exhibited electrophysiological indicators of preserved consciousness.