The emotional homunculus: ERP evidence for independent somatosensory responses during facial emotional processing

Current models of face perception propose that initial visual processing is followed by activation of nonvisual somatosensory areas that contributes to emotion recognition. To test whether there is a pure and independent involvement of somatosensory cortex (SCx) during face processing over and above visual responses, we directly measured participants' somatosensory-evoked activity by tactually probing (105 ms postvisual facial stimuli) the state of SCx during an emotion discrimination task while controlling for visual effects. Discrimination of emotional versus neutral expressions enhanced early somatosensory-evoked activity between 40 and 80 ms after stimulus onset, suggesting visual emotion processing in SCx. This effect was source localized within primary, secondary, and associative somatosensory cortex. Emotional face processing influenced somatosensory responses to both face (congruent body part) and finger (control site) tactile stimulation, suggesting a general process that includes nonfacial cortical representations. Gender discrimination of the same facial expressions did not modulate somatosensory-evoked activity. We provide novel evidence that SCx activation is not a byproduct of visual processing but is independently shaped by face emotion processing.