Covert Speech Comprehension Predicts Recovery From Acute Unresponsive States

Area of Science:

• Neuroscience
• Neurology
• Clinical Neurophysiology

Background:

• Prognostication for patients with traumatic brain injury (TBI) who remain unresponsive after sedation is challenging.
• Uncertainty in prognostication impacts care decisions and rehabilitation resource allocation.
• Identifying covert residual cognition, such as speech comprehension, is crucial for improving prognostic accuracy.

Purpose of the Study:

• To assess residual speech comprehension in unresponsive TBI patients using a passive auditory electroencephalography (EEG) protocol.
• To determine if this measure of speech comprehension can improve neurological prognostication.
• To evaluate the utility of a passive EEG-based marker for bedside prognostication.

Main Methods:

• Recruited 28 TBI patients (2-7 days sedation-free) who failed to obey commands.
• Recorded EEG activity while patients listened to isochronous word streams forming phrases and sentences.
• Quantified cortical tracking of speech rhythm using inter-trial phase coherence, a measure of speech comprehension.

Main Results:

• A significant correlation was found between the strength of cortical tracking of speech and patient outcomes at 3 and 6 months (r > 0.6, p < 0.007).
• The comprehension response strength significantly improved prognostic accuracy compared to clinical factors alone (Glasgow Coma Scale, CT grade).
• Linear regression showed the comprehension response (beta = 0.603, p = 0.006) was a significant predictor of outcome.

Conclusions:

• A simple, passive auditory EEG protocol effectively measures residual speech comprehension in unresponsive TBI patients.
• This EEG-based approach enhances prognostic accuracy during a critical decision-making period.
• The passive nature of the test makes it less susceptible to cognitive deficits, broadening its applicability for prognostication.