Transcranial magnetic stimulation disrupts the perception and embodiment of facial expressions

Abstract

Theories of embodied cognition propose that recognizing facial expressions requires visual processing followed by simulation of the somatovisceral responses associated with the perceived expression. To test this proposal, we targeted the right occipital face area (rOFA) and the face region of right somatosensory cortex (rSC) with repetitive transcranial magnetic stimulation (rTMS) while participants discriminated facial expressions. rTMS selectively impaired discrimination of facial expressions at both sites but had no effect on a matched face identity task. Site specificity within the rSC was demonstrated by targeting rTMS at the face and finger regions while participants performed the expression discrimination task. rTMS targeted at the face region impaired task performance relative to rTMS targeted at the finger region. To establish the temporal course of visual and somatosensory contributions to expression processing, double-pulse TMS was delivered at different times to rOFA and rSC during expression discrimination. Accuracy dropped when pulses were delivered at 60-100 ms at rOFA and at 100-140 and 130-170 ms at rSC. These sequential impairments at rOFA and rSC support embodied accounts of expression recognition as well as hierarchical models of face processing. The results also demonstrate that nonvisual cortical areas contribute during early stages of expression processing.

Figure 1.

The normalized location of the rOFA and the face region of the rSC in one subject.

Figure 2.

Timeline of the trial procedure for experiments 1–3.

Figure 3.

Mean accuracy scores for the expression and identity discrimination tasks in experiment 1. An asterisk denotes a significant difference in Bonferroni's corrected tests.

Figure 4.

Mean accuracy scores for the expression discrimination task in experiment 3. An asterisk denotes a significant difference in Bonferroni's corrected tests.