Abstract:

Recent studies have shown emotional facilitation of sensory processing in the visual cortex and the late positive potential of the event-related-potential (ERP) is enhanced for emotional stimuli in adults. To determine whether the LPP is sensitive to emotional content in adolescence, the present study used ERP to examine the time processing in adolescence and to testify whether the self-reported ratings of valence and arousal to emotional stimulus are covariate with the activation of motivational system in brain.
ERPs were recorded from 48 students aged from 12 to 21 years while they were viewing developmentally appropriated pictures selected from the International Affective Picture System (IAPS). A total of 60 positive, 60 negative and 60 neutral pictures were presented in brief exposure and distinct sequences of every six pictures. For attention concentration, the subjects were instructed to realize a valence categorization task when the pictures offset. The ISI (inter-stimuli interval)varied between 1800ms to 2200ms. Electrophysiological data were collected from the scalp using a 37- channel system. These data were submitted to repeated-measure analysis of variance (MANOVA) with factors of stimuli valence, age, electrode site, and hemisphere.
In all subjects, similar to the result of other emotional patterns, the positive, negative and neutral pictures elicited notable late positive potentials in the picture perception paradigm, which started at about 300ms after onset and might be sustained to 900ms. In all time courses both the positive and negative pictures elicited increased amplitudes as compared to neutral pictures in all subjects from parietal-occipital sites to all scalp regions. As for the age effect on the emotion perception, at frontal, central and temporal sites for late positive potential from 440-580ms, the elder groups showed the greater positivity, whereas the youngest group demonstrated greater at occipital sites. The self-reported ratings suggested clear categorization of the emotional stimulus by the adolescents, and the differential age effects from the ERP were also observed.
In summary, the brain cortical responses to different valence of emotional pictures show generally same trends in the adolescent group: the enhanced late positive potentials, later in the waveform, which were evoked specifically by emotional pictures. This result implies that the motivational meaning of emotion modulates the event-related potential from early age. That the elder group has larger later sustained positivity may reflect the developmental contents. The results also infer that the temporal and the parietal lobe, especially the frontal lobe closely correlate with the developmental effects on emotional processing.

Key words: adolescence, emotional processing, event-related potential (ERP), late positive potential (LPP)