How to calculate the frontal EEG asymmetry

Negative emotions can be associated with a relative activation of the right frontal brain areas and positive emotions with a relative activation in the left frontal area. Empirically, this assumption is based, among other things, on a measurement of the local alpha activity in the EEG (e.g. Davidson, 1995). It applies here that a local decrease in alpha activity is associated with an increase in the activation of an area. The aim of the present study was to investigate the relative activation of the anterior areas in the context of mood induction.
The EEG was derived from 14 right-handed female subjects using 19 standard positions against the bandaged ears. To induce mood, 34 affective positive, neutral and negative images of the International Affective Picture System were presented for eight seconds each. The presentation of the three series of images was interrupted by pauses of six minutes. Rating data and the corrugator EMG demonstrate a systematic effect of mood induction. For EEG epochs without artifacts, an asymmetry index was calculated in the alpha band (8-13 Hz). The analysis was carried out for three different time intervals: For the intervals (1) three seconds before the image presentation and (2) eight seconds during the image presentation there was no effect of the frontal asymmetry. (3.) In the interval of three seconds after the image presentation, systematic effects occur on Fp1-Fp2, F7-F8 and F3-F4. The previous presentation of positive images leads to a relatively stronger activation of left frontal areas compared to negative images.
The data thus support the assumption that the frontal EEG asymmetry differentiates between positive and negative moods. However, the effect only occurs after a picture has been presented. Whether changes in the asymmetry proceed slowly or are overwritten by the processing of the image presentation remains the subject of further analyzes.

Poster in the Emotion and Motivation group, Monday, March 29, 1999, 5: 00-7: 00 p.m., 2nd floor foyer

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