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

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Chapter 1
localization implicated intracerebral sources of these components to lay in inferior
temporal and orbitofrontal brain regions (although few electrode sites were available).
These authors interpret their finding as evidence for increased cortical wiring in
synaesthetes (c.f. Ramachandran and Hubbard, 2001; Bargary and Mitchell, 2008),
but may also be consistent with accounts of synaesthesia which posit differences in
local mechanisms of cortical inhibition (Cohen Kadosh and Walsh, 2008).
In addition to this, two single case studies and one group study have
investigated auditory-visual synaesthesia. In a single case study of acquired auditory-
visual synaesthesia, Rao and colleagues report that synaesthesia inducing sounds
resulted in a modulation of the auditory evoked N1 deflection (Rao, Nobre,
Alexanader and Cowey, 2007). Rizzo and Eslinger (1989) investigated the
electrophysiological correlates of a single case of developmental auditory-visual
synaesthesia, but restricted analysis to three electrode sites (O1/2, or Oz). No
abnormal potentials were found at these three sites, but this does not rule out the
possibility that abnormal potentials may occur at alternative electrode sites. A more
recent group study of tone-colour synaesthesia (n = 10; Goller, Otten, and Ward,
2009) revealed early onset (around 100msec after stimulus onset) differences in
deflections of the auditory evoked potential (auditory N1, N2, and P2). No posterior
difference was observed, implying that synaesthetic experience may be generated
locally (potentially through mechanisms of local differences in cortical inhibition; c.f.
Cohen Kadosh and Walsh, 2008).
1.3.6 Neurocognitive models of synaesthesia
While much research has determined the authenticity of synaesthesia, the
neurocognitive mechanisms which underpin synaesthesia are a subject of uncertainty.
A current area of dispute in the synaesthesia literature is whether synaesthetic