Suppressing sensorimotor activity modulates the discrimination of auditory emotions but not speaker identity

Abstract

Our ability to recognize the emotions of others is a crucial feature of human social cognition. Functional neuroimaging studies indicate that activity in sensorimotor cortices is evoked during the perception of emotion. In the visual domain, right somatosensory cortex activity has been shown to be critical for facial emotion recognition. However, the importance of sensorimotor representations in modalities outside of vision remains unknown. Here we use continuous theta-burst transcranial magnetic stimulation (cTBS) to investigate whether neural activity in the right postcentral gyrus (rPoG) and right lateral premotor cortex (rPM) is involved in nonverbal auditory emotion recognition. Three groups of participants completed same-different tasks on auditory stimuli, discriminating between the emotion expressed and the speakers' identities, before and following cTBS targeted at rPoG, rPM, or the vertex (control site). A task-selective deficit in auditory emotion discrimination was observed. Stimulation to rPoG and rPM resulted in a disruption of participants' abilities to discriminate emotion, but not identity, from vocal signals. These findings suggest that sensorimotor activity may be a modality-independent mechanism which aids emotion discrimination.

Figure 1.

Summary of cTBS and task protocol in experiments 1 and 2. Participants completed a same–different auditory emotion (experiment 1) or identity (experiment 2) matching task. Both experiments consisted of three testing sessions conducted over three nonconsecutive days. At each testing session one of the three brain regions was stimulated (rPoG, rPM or the vertex) and each task was completed before and 5 min following cTBS to each site. The 5 min rest period was based on the observed time course of effects seen in the motor cortex (Di Lazzaro et al., 2005; Huang et al., 2005).

Figure 2.

Summary of cTBS sites stimulated, rPoG (a) and rPM (b). Locations of cTBS were determined using the Brainsight coregistration system. To ensure that any differences observed were not due to nonspecific effects of cTBS, the vertex was stimulated as a cTBS control site.

Figure 3.

Magnitude of disruption or facilitation (mean ± SEM) in milliseconds following cTBS targeted at rPoG, rPM and the vertex (experiments 1 and 2). To determine whether the magnitude of impairment following cTBS stimulation differed across the sites and tasks we calculated the difference between the post-cTBS and pre-cTBS baseline reaction times (±3 SDs and all errors removed; and corrected for accuracy) for each condition (i.e., baseline RT/accuracy minus post-cTBS RT/accuracy for each site stimulated across tasks). A disruption in reaction times following stimulation is shown by a negative value and facilitation by a positive value. a, For the emotion discrimination task (experiment 1), participants (n = 10) were impaired in their abilities to discriminate between the auditory emotions of others following stimulation to rPoG and rPM compared with stimulation at the vertex (cTBS control site). b, This was not found to be the case when participants (n = 10) had to discriminate auditory identity (experiment 2)—the effects of cTBS targeted at rPoG, rPM and the vertex did not significantly differ between the sites stimulated, and there was a trend for facilitation at all sites. Between-group comparisons also revealed that the disruption in performance on the emotion-discrimination task following cTBS to rPoG and rPM was significantly different to the facilitation shown in the identity task. No significant difference between emotion discrimination and identity discrimination task performance was found following cTBS at the vertex. *p < 0.05.