The Influence of Visual Induction of Positive-negative Emotions on the Somatosensory Cortex

To examine changes in somatosensory cortical activity associated with the processing of emotional images, we measured steady-state somatosensory evoked fields (SS-SEFs) of magnetoencephalograms (MEGs) under tactile stimulation. 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. Those images, along with synchronous tactile stimuli, were randomly presented for 2.0 s using a video projector and a screen set at 120 cm in front of the subject. The tactile stimuli were applied to the tip of the right index finger. A stimulus epoch consisted of a 2.0 s period of vibration at 10-Hz or 20-Hz and a silent period of 1.0 s. At least 50 epochs were recorded for off-line averaging of the MEG signals for each condition of negative, positive, or neutral images, according to the prior categorization by each subject. The amplitude of the SS-SEF was larger for the negative impression images than for the neutral impression images (p < 0.05), suggesting that the amplitude of the SS-SEF that originated from the somatosensory cortex was modulated by the visual emotional stimuli.