On ERPs detection in disorders of consciousness rehabilitation

Abstract

Disorders of Consciousness (DOC) like Vegetative State (VS), and Minimally Conscious State (MCS) are clinical conditions characterized by the absence or intermittent behavioral responsiveness. A neurophysiological monitoring of parameters like Event-Related Potentials (ERPs) could be a first step to follow-up the clinical evolution of these patients during their rehabilitation phase. Eleven patients diagnosed as VS (n = 8) and MCS (n = 3) by means of the JFK Coma Recovery Scale Revised (CRS-R) underwent scalp EEG recordings during the delivery of a 3-stimuli auditory oddball paradigm, which included standard, deviant tones and the subject own name (SON) presented as a novel stimulus, administered under passive and active conditions. Four patients who showed a change in their clinical status as detected by means of the CRS-R (i.e., moved from VS to MCS), were subjected to a second EEG recording session. All patients, but one (anoxic etiology), showed ERP components such as mismatch negativity (MMN) and novelty P300 (nP3) under passive condition. When patients were asked to count the novel stimuli (active condition), the nP3 component displayed a significant increase in amplitude (p = 0.009) and a wider topographical distribution with respect to the passive listening, only in MCS. In 2 out of the 4 patients who underwent a second recording session consistently with their transition from VS to MCS, the nP3 component elicited by passive listening of SON stimuli revealed a significant amplitude increment (p < 0.05). Most relevant, the amplitude of the nP3 component in the active condition, acquired in each patient and in all recording sessions, displayed a significant positive correlation with the total scores (p = 0.004) and with the auditory sub-scores (p < 0.00001) of the CRS-R administered before each EEG recording. As such, the present findings corroborate the value of ERPs monitoring in DOC patients to investigate residual unconscious and conscious cognitive function.

Keywords: CRS-R; ERP; P300; acquired brain injury; consciousness; minimally conscious state; vegetative state.

Figure 1

Time sequence of standard, deviant and novel (SON) stimuli administered through the auditory oddball paradigm.

Figure 2

Grand average of ERP waveforms depicted at Cz during passive (A) and active (B) listening of patients' own name (novel stimulus), in both group of patients. Black and red traces code for VS and MCS group, respectively. The right side panels illustrate the scalp nP3 topographies at Cz. Color bar code for the amplitudes of the scalp maps obtained at the time point of ERP maximum peak.

Figure 3

Average of ERP waveforms and scalp potential topography depicted at Cz of passive condition related to the first and to the second recording session, in patients who underwent a change in their clinical status, according to the CRS-R. Color bar code for the amplitudes of the scalp maps and give the size of the nP3 projections at the time point of the maximum peak.

Figure 4

The two scatter plots show the linear correlation between nP3 amplitude individual values in the active condition and the JFK CRS-R overall scores (panel A) and auditory sub-scores (panel B). VS and MCS patients are represented by circle and square, respectively.