Spatial Properties of Mismatch Negativity in Patients with Disorders of Consciousness

Abstract

In recent decades, event-related potentials have been used for the clinical electrophysiological assessment of patients with disorders of consciousness (DOCs). In this paper, an oddball paradigm with two types of frequency-deviant stimulus (standard stimuli were pure tones of 1000 Hz; small deviant stimuli were pure tones of 1050 Hz; large deviant stimuli were pure tones of 1200 Hz) was applied to elicit mismatch negativity (MMN) in 30 patients with DOCs diagnosed using the JFK Coma Recovery Scale-Revised (CRS-R). The results showed that the peak amplitudes of MMN elicited by both large and small deviant stimuli were significantly different from baseline. In terms of the spatial properties of MMN, a significant interaction effect between conditions (small and large deviant stimuli) and electrode nodes was centered at the frontocentral area. Furthermore, correlation coefficients were calculated between MMN amplitudes and CRS-R scores for each electrode among all participants to generate topographic maps. Meanwhile, a significant negative correlation between the MMN amplitudes elicited by large deviant stimuli and the CRS-R scores was also found at the frontocentral area. In consequence, our results combine the above spatial properties of MMN in patients with DOCs, and provide a more precise location (frontocentral area) at which to evaluate the correlation between clinical electrophysiological assessment and the level of consciousness.

Keywords: Disorder of consciousness; EEG; Minimally conscious state; Mismatch negativity; Vegetative state.

Fig. 1

Stimulus sequences. 1000 pure sound stimuli (lasting for 200 ms) with SOA of 1011 ms were presented to a subject in order to elicit the MMN ERP response. The frequencies of standard, small deviant and large deviant stimuli were 1000 Hz, 1050 Hz and 1200 Hz, and the numbers of trials were 800, 100 and 100.

Fig. 2

Grand averaged waveforms and topographies. A Grand averaged waveform of responses to small deviant stimuli and the sweep before it at electrode Fz. B Grand averaged waveform of responses to large deviant stimuli and the sweep before it at electrode Fz. C Grand averaged difference waves (at electrode Fz) of large (black line) and small (blue line) deviant stimuli. D Topography of mean MMN amplitude within the time window (time window of small deviant: 189 ms–229 ms; time window of large deviant: 258 ms–298 ms).

Fig. 3

The correlation between MMN amplitude and CRS-R scores. A The correlation between MMN amplitude at electrode Cz and CRS-R scores (r_l2/r_s2 represents the correlation coefficient between MMN amplitude derived by large/small deviant stimuli and CRS-R scores). B The different shades on the topography represent the degree of association between the MMN amplitude across different electrode sites and CRS-R scores.

Fig. 4

Spatial properties of the correlation between MMN and the CRS-R scores. A Statistical parametric maps showing scalp regions where there is a significant interaction effect between conditions (small and large deviant stimuli) and electrode nodes, with the threshold at P < 0.05. B Statistical parametric maps showing scalp regions where there is a significantly negative correlation between the MMN amplitudes elicited by large deviant stimuli and the CRS-R scores, with the threshold at P < 0.05. C Topography showing scalp regions where both the interaction effect (between conditions and electrode nodes) and negative correlation (between the MMN amplitudes elicited by large deviant stimuli and the CRS-R scores) are significant.