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

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Chapter 8
processed by a single “expression system” and that expression-general and
expression-specific representations may interact at varying levels of processing. The
lack of impairment on disgust recognition found here may reflect the fact that the
neural noise introduced in rSI by TMS is better compensated for by emotions which
have more alternative mechanisms / expression-specific representations elsewhere in
the brain. For example, there is a good degree of evidence from functional brain
imaging (Phillips et al., 1997, 1998; Sprengelmeyer, Rausch, Eysel, and Przuntek,
1998), intracerebral recording (Krolak-Salmon et al., 2003), and neuropsychological
studies (Calder et al., 2000; Kipps, Duggins, McCusker, and Calder, 2007) which
indicate that the anteroventral insula acts as an expression-specific mechanism for
disgust recognition. The anteroventral section of the insula is connected to number of
regions which are thought to be involved in emotion processing across modalities
(including the primary somatosensory cortex, basal ganglia, amygdala, orbitofrontal
cortex and superior temporal cortex; Augustine, 1996; Flynn, Benson, and Ardila,
1999; Mesulam and Mufson, 1982) and has been suggested to act as a point of
convergence for sources involved in the processing of disgust recognition to varying
degrees (Kipps et al., 2007). It is feasible that suppressing rSI with cTBS reduces
one, of the multiple sources, of information which contributes to disgust processing in
this section of insula, and therefore does not result in impairment. It is also possible
that with alternative paradigms (e.g. same-different expression matching paradigms as
opposed to a forced-choice paradigm which could bias responses of disgust and
thereby facilitate performance) and stimuli (e.g. dynamic stimuli as opposed to static),
stimulation to rSI may lead to a disruption of participants’ abilities to recognise
disgusted facial expressions (c.f. Chapter 7; Pitcher et al., 2008).