Evaluation of phase-locked and non-phase-locked MEG activities under emotional stimuli

The present study investigates phase-locked and non-phase-locked brain responses in theta and alpha frequency bands. A 122-ch whole-head magnetoencephalogram (MEG) was recorded continuously during emotional audio-visual stimuli. The results showed that emotional stimuli induced increased theta band phase-locked activity at 200-400 ms and non-phase-locked activity at 100-600 ms. These activities were stronger with pleasant stimuli over all areas compared with the baseline period. In addition, decreased alpha1 band non-phase-locked activity was shown at 600-1000 ms in the pleasant and around 800-1000 ms in the unpleasant stimuli over the occipital cluster. These results indicate that emotional processing induces increased brain activity in the theta frequency band soon after the onset of the stimuli.