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

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Chapter 6
(EBA; thought to be functionally specialised for body processing) has been shown to
impair body but not face or object recognition (Pitcher et al., 2009) – this dissociation
is particularly striking given the anatomical adjacency between these regions.
Functional dissociations such as the triple dissociation described above demonstrate
the functional focality of TMS and have been regularly observed across a variety of
domains (e.g. Ashbridge, Walsh, and Cowey, 1997; Stewart, Walsh, Frith, and
Rothwell, 2001).
A further approach to assess the spatial specificity of TMS is to combine the
approach with methods such as fMRI, MEG or PET. To date, studies that have
combined these methodologies have demonstrated a good correspondence between
TMS defined functional regions and the areas revealed with high spatial resolution
brain imaging techniques (Bestmann, Baudewig, Siebner, Rothwell, and Frahm, 2004;
Bohning, Shastri, McConnell, Nahas, Lorberbaum, and Roberts, 1999; Ruff et al.,
2006; Siebner et al., 1998; Terao et al., 1998).
In sum, while the effects of TMS will dissipate from the targeted region to
other cortical areas, the functionally effective resolution is much more discrete
(approximately 1cm). This has been demonstrated across a variety of studies by
systematically measuring the effect on behaviour as the coil is moved away from an
optimal stimulation site (e.g. by stimulating adjacent areas of cortex [Figure 6.5]
which demonstrate functionally different characteristics or examining direct
physiological effects).