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

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Chapter 6
trial. The later has the advantage of reducing the number of temporal conditions in a
TMS timing experiment.
It is also possible that the disruption induced by multiple pulses of TMS will
summate, therefore inducing larger behavioural impairments. The potential for
summation of the disruptive effect has been further exploited by repetitive TMS
(rTMS) protocols. For example, Rushworth and colleagues (2001) delivered TMS at
a frequency of 10 Hz for 500 ms and showed dissociations between parietal regions
(supramarginal gyrus and angular gyrus) for mediating modality-specific attentional
processes. To date there is no corroborating physiological evidence that the five
pulses of TMS actually do summate, but despite this the approach has proven to be a
robust online TMS protocol for demonstrating function-specific involvement of a
wide variety of cortical areas across a number of domains (e.g. Beck, Muggleton,
Walsh, and Lavie, 2006; Bjoertomt, Cowey, and Walsh, 2002; Campana et al., 2002;
Lavidor and Walsh, 2003; Pitcher et al., 2008; Pitcher et al., 2009; Wig, Grafton,
Demos, and Kelley, 2005).
In contrast to online TMS paradigms which rely upon observing effects in
very short-lasting temporal windows, a recently introduced paradigm of offline
continuous theta-burst stimulation (cTBS) provides a more long lasting window for
one to examine changes in cortical function on behaviour. cTBS is a form of rTMS
based on the burst patterns used to induce long lasting changes in synaptic
effectiveness in animal experiments. The approach uses high frequency stimulation
bursts (3 pulses at 50Hz), which are repeated at intervals of 200 milliseconds (i.e.
5Hz). In the motor system cTBS to M1 suppresses the excitability of motor cortical
circuits for 20-60 minutes depending on the cTBS parameters used (Di Lazzoro et al.,
2005; Di Lazzoro et al., 2008; Huang, Edwards, Rounis, Bhatia, and Rothwell, 2005;