|| We recorded a slow negative potential from Cz (10/20 method) in 49 healthy students (12 male, 37 female, mean age 19.1) by a short interstumulus interval CNV paradigm. The interstimulus interval was 2 or 3 seconds, the warning stimulus presented at random or regular interval at 0.2 Hz. An atypical negative variation with two separated negative peaks was recorded in 26.0-30.6% trials regardless of interstimulus interval or modality of warning stimulus presentation, while a typical CNV was recorded in 32.0-59.2% of trials. No apparent negative variation was recorded in 14.3-18.4% in 2 seconds interstimulus interval, and 28-38% in 3 seconds interstimulus interval, showing that 2 seconds interval is better to get stable CNV recording than 3 seconds interval. The first negative wave of the atypical negative variation was 692-799msec in duration, but frequently prolonged to 1000msec or more in 3 seconds interval. It usually had negative peak around 900-1100msec, but sometimes around 1500msec. This features are different from any reported negative components of CNV. The second negative wave began 800-1200msec before second stimulus, and had its peak just before second stimulus, showing common features with readiness potential. The appearance of CNV was unsatble in the students in which the atypical negative variation was recorded in regular, 2 seconds intersitimulus interval, and the amplitude of slow vertex response and pattern reversal visual evoked potential was lower in thses students than in the students in which a typical CNV was recorded more than 3 times in total 4 times of trials. These findings indicate that the atypical variation observed in this study is due to a lowered arousal level or cortical neuronal activity, rather than a separated appearance of different components of CNV.