Abstract: Introduction
A number of studies have investigated how brain activity is modulated by emotion. These studies found some important general emotion effects in event-related potentials (ERPs), such as negativity bias, early posterior negativity and late positive potential (LPP). However, it is not clear how time processing of emotion is influenced by individual differences, especially in negative emotion. According to Eysenck’s theory, personality trait of neuroticism is strongly associated with negative emotion, which has been supported by many behavioral studies. The present study used ERP to explore how time processing of negative emotion is modulated by levels of neuroticism.

Methods
ERPs were recorded from 15 high and 15 low neurotic participants. These participants were selected from 292 college students based on their scores in neuroticism of Eysenck Personality Questionnaire-Revised, Short Scale for Chinese (EPQ-RSC). These participants were presented slides of International Affective Picture System (IAPS) posing 50 positive, 50 neutral and 50 negative pictures, which were displayed for 1000 ms and presented serially in sequences of six pictures. To ensure that the subjects were attending to the pictures, a valence categorization task was introduced. The ITI (inter-trial interval) varied between 1000 ms and 2000 ms. Electrophysiological data were collected from the scalp using a 37-channel system. These data were submitted to repeated-measure analysis of variance (ANOVA) with factors of stimuli valence (3 levels: positive, neutral, negative), neuroticism (2 levels: high, low), electrode site (8 levels: F3, Fz, F4, Fc3, Fcz, Fc4, T5, T6), and hemisphere (2 levels: left, right).

Results
The results showed that the components of P120, N130, P230 and N250 exhibited a main effect of stimuli valence, reflecting greater ERP mean amplitudes for positive and negative as compared to neutral content. The difference begins with 120 ms after stimulus onset. Furthermore, the interaction of Neurotic level and Stimuli valence is significant for LPP mean amplitude over frontal and frontal-central leads (F(1, 28)= 6.52, p<0.1). This effect indicated that high neurotic subjects, compared with low neurotic ones, exhibited smaller LPP to negative pictures, while they did not display differences in the response to positive and neutral pictures.

Conclusions
The early emotion effect about 120 ms suggests that early cognitive processing can be influenced and modulated by emotion. The LPP effect supports the view that negative emotion processing of brain is modulated by levels of neuroticism, and the influence is mainly reflected on late processing of negative emotion at frontal and frontal-central sites. The decreased LPP amplitude in high neurotic subjects may be the result of greater habituation in sessions with a large number of trials

Key words: emotion, neuroticism, event-related potentials (ERPs), late positive potential (LPP)