Steady-State Visually Evoked Fields (SSVEF) associated with affective emotions

The aim of this study was to examine the SSVEFs associated with the processing of positive and negative impression images. We used the International Affective Picture System (IAPS) which is increasingly used in brain imaging studies to examine emotional processes. Their images also allow valence to be systematically investigated. All 200 images were categorized into three categories of "negative ", "positive " and "neutral " individually according to valence assessed by each subject after the MEG measurement. The peripheral square, i.e., frame, of the image was flickered black and white at 15 Hz while the image was kept stationary. Those images were randomly presented for 2.0 s on screen set at 120 cm in front of the subject. Ten healthy subjects participated. MEG recordings were made with a 122-channel whole-head MEG system in a magnetically shielded room. We made two-dipoles estimation of the averaged MEG signals and obtained the amplitude of souse waveform in 15 Hz component (using a band-pass filter at 14-16 Hz) of SSVEF in occipital area. The amplitude of the SSVEF source in the occipital area was larger for the negative impression images than the positive impression images (p<0.05). This result suggests that the amplitude of SSVEF that originated from the surrounding field of visual object was modulated by the emotional object and that the SSVEF could be a measure of emotion of subjects.