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

166
Chapter 9
connectivity (i.e. structural differences; Bargary and Mitchell, 2008; Rouw and
Scholte, 2007), others in favour of malfunctions in cortical inhibition (i.e. functional
but not structural differences; Cohen Kadosh and Henik, 2007; Cohen Kadosh and
Walsh, 2008; Grossenbacher and Lovelace, 2001), and others for a combination of
both (Smilek, Dixon, Cudahy, and Merikle, 2001). In principle, the findings of
enhanced sensory perception in synaesthesia could be accounted for by any of these
approaches (e.g. mechanisms of inhibition may unmask local anatomical pathways,
while altered connectivity may result in alternative local and widespread anatomical
pathways which could facilitate performance). Moreover, compatible findings of
sensory-enhancement in the deprived brain would suggest that both aberrant
connectivity and malfunctions in cortical inhibition could play a role in the sensory-
enhancement found in synaesthetes. For example, temporary enhancements in tactile
acuity can occur following blindfolding, and are thought to be due to fast-acting
unmasking of existing connections to maintain functional behaviour. In comparison,
tactile acuity can also be enhanced in blindness, which is though to reflect sustained
unmasking of existing connections leading to new local and widespread anatomical
pathways (a slow-acting mechanism; Pascual-Leone, Amedi, Fregni, and Merabet,
2005). Future studies should investigate how and whether mechanisms of cortical
inhibition and connectivity interact in synaesthesia, and assess the possibility that
increased structural connectivity in synaesthesia (Rouw and Scholte, 2007) may
reflect sustained unmasking of existing connections (Cohen Kadosh et al., 2009). A
further intriguing possibility would be to examine the interaction between fast-acting
cortical unmasking mechanisms in sensory-enhancement following deprivation and
synaesthesia. For example, if temporary enhancements in tactile acuity following
blindfolding are linked to perceptual unmasking, and synaesthesia is linked to reduced