[Mismatch negativity in patients with multiple and severe handicaps]

Mismatch negativity (MMN) of the event related potential (ERP) is generated when patients can discriminate two different kinds of stimuli even if he or she is not conscious of their differences. The authors examined auditory ERPs of passive paradigm in 16 patients with severe multiple handicaps. All patients showed no or scarce clinical response to human voices or environmental sounds. This study investigated whether they showed MMN, since it is hard to evaluate their auditory perception clinically. Auditory stimuli were the tone bursts of 700 and 1,000 Hz in frequency offered at a 4:1 occurrence. Nine of 16 patients showed a definite N2 wave followed by an N 1 wave. The latency of the N 2 wave ranged from 150 to 596 milliseconds after the onset of the target stimuli. This N 2 was considered compatible with mismatch negativity (MMN) in healthy patients. These results suggest that the patients could discriminate subtle difference in two kinds of tones, although their responses to auditory stimuli were very poor.