Mirror-touch synaesthesia: the role of shared ... - UCL Discovery

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Chapter 8
necessary for all or only some distinct facial expressions is a matter of debate. To
date only two transcranial magnetic stimulation studies have addressed the necessity
of the right somatosensory cortex in healthy adults. In one study, two emotional
expressions (fear and happiness) and single pulse TMS over right somatosensory
cortex were used to investigate the necessity of this brain region for emotion
recognition in healthy adults. These authors observed an expression-selective TMS-
related interference following stimulation of right somatosensory cortex during the
recognition of fearful, but not happy expressions (Pourtois et al., 2004). In contrast, a
more recent repetitive TMS study (Pitcher et al., 2008), using six emotional
expressions (anger, disgust, fear, happiness, sadness and surprise), found an
expression-general impairment following stimulation of the right somatosensory
cortex. Further study is needed to clarify this discrepancy.
Furthermore, in both previous TMS studies a same-different matching task
was used to assess participants’ expression recognition abilities. The nature of these
tasks requires some degree of working memory in which the participant must not only
recognize a sample expression but store the information in memory to match it to a
sequential expression. Therefore it is difficult to disentangle whether TMS
impairment results from a disruption of fronto-parietal working memory networks (cf.
Harris, Harris, and Diamond, 2001; Mottaghy, Gangitano, Sparing, Krause, and
Pascual-Leone, 2002; Oliveri et al., 2001) or sensorimotor simulation mechanisms per
se 4 .
To address this, this study sought to establish: i) whether neural activity in the
right primary somatosensory cortex (rSI) and right inferior frontal gyrus (rIFG) is
central to recognizing the facial expressions of others and ii) whether, at the cortical
4 Note that this is controlled for in Chapter 7 because of the task-specific dissociation observed.