Cognitive Processing in Non-Communicative Patients: What Can Event-Related Potentials Tell Us?

Zulay R Lugo,Cornelia Herbert,Fréderic Pellas,Donatella Mattia,Sandra Veser,Damien Lesenfants,Andrea Kübler,Steven Laureys,Christoph Guger,Luigi Bianchi,Lucia R Quitadamo,Boris Kotchoubey,Quentin Noirhomme,Ruben G L Real

doi:10.3389/fnhum.2016.00569

Abstract

Event-related potentials (ERP) have been proposed to improve the differential diagnosis of non-responsive patients. We investigated the potential of the P300 as a reliable marker of conscious processing in patients with locked-in syndrome (LIS). Eleven chronic LIS patients and 10 healthy subjects (HS) listened to a complex-tone auditory oddball paradigm, first in a passive condition (listen to the sounds) and then in an active condition (counting the deviant tones). Seven out of nine HS displayed a P300 waveform in the passive condition and all in the active condition. HS showed statistically significant changes in peak and area amplitude between conditions. Three out of seven LIS patients showed the P3 waveform in the passive condition and five of seven in the active condition. No changes in peak amplitude and only a significant difference at one electrode in area amplitude were observed in this group between conditions. We conclude that, in spite of keeping full consciousness and intact or nearly intact cortical functions, compared to HS, LIS patients present less reliable results when testing with ERP, specifically in the passive condition. We thus strongly recommend applying ERP paradigms in an active condition when evaluating consciousness in non-responsive patients.

Highlights

The diagnosis of the presence of consciousness in non-responsive patients due to severe brain injury is a challenging task
We investigated P300 modulation in a passive and active oddball paradigm in healthy participants and locked-in syndrome (LIS) patients to determine whether P300 amplitude increases from passive to active tasks in a similar way in both groups (LIS patients and healthy controls (HC))
Contrary to our expectation not all the patients with LIS displayed a P300 in the passive condition—only three out of seven- and the significant increase when passing from passive to active tasks in amplitude and latency could only be confirmed in the group of healthy participants

Summary

INTRODUCTION

The diagnosis of the presence of consciousness in non-responsive patients due to severe brain injury is a challenging task. Regarding the assessment of the presence of the P300 waveform in patients with LIS, studies have shown similar responses to healthy controls (HC) both in passive (Perrin et al, 2006) and active (Schnakers et al, 2009a) conditions to semantic paradigms but not in following commands in brain computer interface (BCI) tasks (Lulé et al, 2013). A test, to be used in the context of an acute medical setting, should be sufficiently sensitive to detect signals of conscious mental processing and at the same time short enough to be used despite the fluctuations of vigilance and short attentional span of these patients To provide such a test, we investigated an auditory oddball paradigm to elicit the P300 component in a passive and an active condition in a group of HC and in a group of LIS patients. The presence of these changes would demonstrate the applicability of the paradigm to detect consciousness in non-responsive patients

MATERIALS AND METHODS

Experimental Procedure

RESULTS

DISCUSSION