A framework for the extended monitoring of levels of cognitive function in unresponsive patients.

Richard L Mah,John F Connolly,Lawrence M Ward

doi:10.1371/journal.pone.0200793

Richard L Mah, John F Connolly + Show 1 more

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https://doi.org/10.1371/journal.pone.0200793

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Journal: PloS one	Publication Date: Jul 19, 2018
Citations: 6	License type: CC BY 4.0

Affiliation: McMaster University

Abstract

Generally, prognostication of coma outcome currently combines behavioral, reflex, and possibly neuroimaging tests that are interpreted by an attending physician. Electroencephalography, particularly, event-related brain potentials (ERP) have received attention due to evidence demonstrating the positive predictive value of certain ERP including the mismatch negativity (MMN) and the P3a, for coma emergence. We describe a set of ERP paradigms designed to require and reflect increasing levels of cognitive processing with the added objective of determining the influence of each paradigm’s context strength on its ability to elicit ERPs. These paradigms were then used without explicit instructions to participants to attend to the stimuli to determine which paradigms possessed sufficient context “strength” to elicit ERPs in the absence of active participation on the part of the subject; a circumstance often encountered in brain injury patients. These paradigms were then validated on two groups of adults–younger and older, and the difference due to active participation was validated on another group of younger adults. Results show that paradigms with stronger stimulus context features performed better than those with weaker contexts, and that older adults generally had significantly attenuated and delayed responses compared to younger adults. Based on these findings, it is recommended the use of the auditory oddball paradigm that includes novel stimuli to elicit the mismatch negativity and P300, and semantic violation sentences to elicit the N400. These findings also reinforce the procedure of instructing participants about the requirements of a protocol–regardless of the patient’s diagnosis or apparent state–in order to help those who are able to attend to show the most robust responses possible.

Highlights

The use of event related potentials (ERPs) for the assessment of patients in altered states of consciousness has been a topic of research for the past few decades
A framework for the extended monitoring of levels of cognitive function in unresponsive patients studies involved the use of the P300 in non-traumatic comas, where the presence of the P300 was correlated with positive outcomes [1,2,3]
It is clear that waveform morphology differed between the two groups with younger adults exhibiting a small post-mismatch negativity (MMN) positivity (P200) but no such response being seen in older adults

Summary

Introduction

The use of event related potentials (ERPs) for the assessment of patients in altered states of consciousness has been a topic of research for the past few decades. Since the MMN has been strongly elicited irrespective of attention, they believed it to be a more reliable measure for patients in altered states of consciousness [5, 6]. This study showed that in each case the MMN was detected, the patient would soon regain consciousness. They noted that the “MMN response is the earliest available indicator of awakening from coma” while acknowledging that the MMN “does not provide prognostic information about functional outcome, [but] it may help to define objectively the duration of coma” [4]

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