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

147
TMS Protocol and Site Localisation
Chapter 8
TMS was delivered via a figure of eight coil with a 70mm diameter using a
Magstim Super Rapid Stimulator (Magstim, UK). An offline continuous theta burst
TMS paradigm was used to prevent any influence of proprioceptive effects of TMS on
reaction time performance (Terao et al., 1997). The parameters were identical to
those used in Chapter 7. TMS machine output was set to 80% of each participant’s
motor threshold with an upper limit of 50% of machine output. Motor threshold was
defined using visible motor twitch of the contralateral first dorsal interosseus
following single pulse TMS delivered to the best scalp position over motor cortex and
was calculated using a modified binary search paradigm (MOBS; Tyrell and Owens,
1988). For each subject, motor threshold was calculated following pre-TMS baseline
and prior to coregistration.
Following the pre-TMS block, locations for TMS were identified using
BrainSight TMS-magnetic resonance coregistration system (Rogue Research,
Montreal, Canada). FSL software (FMRIB, Oxford) was used to transform
coordinates for each site to each subject’s individual MRI scan (Figure 1a, b, c).
Talairach coordinates for rSI (27, -27, 69) were taken from Blakemore and colleagues
(2005) and were averages for twelve neurologically normal subjects in an fMRI study
following touch to their own face (the same rSI site as that used in Chapter 7). The
MNI coordinates for rIFG (60, 8, 6) were the averages of twelve neurologically
normal subjects in an fMRI study of facial emotion (Hennenlotter et al., 2005) and the
region broadly corresponding to BA 44 of the inferior frontal gyrus. Coordinates for
V5 / MT (44, -67, 0) were taken from Dumoulin and colleagues (2000). In addition to
BrainSight coregistration, V5 / MT was also confirmed functionally using
phosphenes.