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

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Chapter 3
Leone, 2002) – further implying that elevated sensory sensitivity may be linked to
mechanisms of cross-modal plasticity rather than additional sensory experience.
Two mechanisms of cross-modal plasticity have been suggested to account for
compensatory changes in the deprived brain: cortical unmasking of pre-existing
connections and cortical reorganisation (e.g. Pascual-Leone et al., 2005; Wittenberg et
al., 2004). Mechanisms of cortical unmasking (through processes such as
disinhibition) involve the strengthening of existing within and between region
anatomical pathways (i.e. functional but not structural differences), while mechanisms
of cortical reorganisation involve the establishment of new local and widespread
anatomical connections (i.e. structural differences). The role of these mechanisms on
compensatory change is thought to reflect differences in the speed of plasticity, with
unmasking representing a form of rapid change which if sustained leads to long
lasting cortical changes such as the establishment of new anatomical connections
(slow acting mechanism; Pascual-Leone et al., 2005). For example, in the case of
temporary enhancements in tactile acuity following blindfolding, unmasking of
existing connections may offer a fast-acting mechanism of cross-modal plasticity to
maintain functional behaviour (i.e. perception of the environment through rapid
enhancements in tactile processing). In comparison, in the case of enhanced tactile
processing in the blind, sustained unmasking of existing connections may lead to new
local and widespread anatomical pathways resulting in long lasting enhancements in
tactile acuity which aid in daily life (Pascual-Leone et al., 2005).
There is growing evidence that synaesthesia may act upon the ‘normal’
architecture for cross-modal interactions (see Sagiv and Ward, 2006 for review) and
parallels may be drawn between mechanisms of cross-modal plasticity following
compensatory changes in the deprived brain and those which have been suggested to