Fast vigilance decrement in closed head injury patients as reflected by the mismatch negativity (MMN)

Event-related potentials (ERPs) were measured from 24 chronic closed head i njury (CHI) patients and 18 age- and education-matched controls. The oddbal l paradigm was applied while subjects were watching a silent movie. The sta ndard (P=0.8) sound of 75 ms duration had a basic frequency of 500 Hz with harmonic partials of 1000 Hz and 1500 Hz, whereas these frequencies for the pitch deviant were each 10% higher. The frequencies of the duration devian t matched with those of the standard but was 25 ms in duration. The MMN (mi smatch negativity), generated by the brain's automatic auditory change-dete ctor mechanism, was elicited by both deviants. No significant differences i n the MMN latency or amplitude for either pitch or duration deviants were f ound between the groups. However, the MMN amplitude for the pitch deviant d ecreased in the patient group during the experiment considerably faster tha n in controls, suggesting a faster vigilance decrement in the patients. Neu roReport 12:1517-1522 (C) 2001 Lippincott Williams & Wilkins.