Spatiotemporal Analysis of Event-related Current Density Reveals Dissociable Effects of Arousal and Valence on Emotional Picture Processing

Abstract

Background: The processing of emotional visual stimulation involves the processing of emotional and visuoperceptual information. It is not completely revealed how the valence and arousal affect these two aspects. The objective was to investigate the effects of valence and arousal on spatiotemporal characteristics of cortical information processing using distributed source imaging of event-related current density (ERCD).

Methods: Electroencephalograms (64 channels) were recorded from 19 healthy men while presenting affective pictures. Distributed source localization analysis was adopted to obtain the spatiotemporal pattern of ERCD on cortical surface in response to emotional visual stimulation. A nonparametric cluster-based permutation test was used to find meaningful time and space without prior knowledge.

Results: Significant changes of ERCD in 400-800 ms among positive, negative, and neutral emotional conditions were found in left posterior cingulate cortex (PCC) and right inferior temporal cortex (ITC). In the PCC, the stimuli with higher arousal levels showed more negative ERCD than neutral stimuli. In the ITC, the ERCD for negative stimuli was significantly more negative than those of positive and neutral ones.

Conclusion: Arousal and valence had strong influence on memory encoding and visual analysis at late period. The location and time showing significant change in neural activity according to arousal and valence would provide valuable information for understanding the changes of cortical function by neuropsychiatric disorders.

Keywords: Arousal; Electroencephalograms; Emotion; Event-related Current Density; Spatiotemporal Analysis; Valence.

Fig. 1. Experimental task.

Fig. 2. Illustration of the procedure for finding spatiotemporal regions correspoding to significant differences between conditions using nonparametric cluster-based permutation test. (A) Calculation of univariate test-statistics at all the points in time-vertex space. (B) Left: selected regions in time-vertex space with high test-statistics. If two points are continuous with respect to either time and vertex, they are grouped as a cluster as shown. Three clusters with P < 0.05 are shown, along with the sum of test-statistics within each cluster. Right: The clusters with high sum of test-statistics are determined based on the null distribution obtained from random permutation.

ERCD = event-related current density.

Fig. 3. Arousal and valence levels of emotional stimuli. (A) Distribution of arousal and valence levels of visual stimuli. (B) Statistical comparison of the valence and arousal level (^***P < 0.001, Bonferroni corrected, independent t-test).

Fig. 4. Cortical regions showing significant event-related current density differences between the three emotion conditions. Among the six region of interests which were determined by the cluster-based permutation test, only two are displayed for simplicity (left PCC [green] and right ITC [blue]).

PCC = posterior cingulate cortex, ITC = inferior temporal cortex.

Fig. 5. Spatiotemporal characteristics of the two ROIs (left PCC and right ITC). (A) The time-series of the ERCD at the left PCC and its statistical comaprison among emotional categories. (B) The time-series of the ERCD at the right ITC and its statistical comaprison among emotional categories. Error bars denote standard errors.

ERCD = event-related current density, PCC = posterior cingulate cortex, ROI = region of interest, ITC = inferior temporal cortex. ^*P < 0.05; ^**P < 0.01; pairwise t-test, FDR corrected.