ASSOCIATIVE SEQUENCE LEARNING: THE ROLE OF EXPERIENCE IN THE
DEVELOPMENT OF IMITATION AND THE MIRROR SYSTEM
Supplementary Methods
rTMS experiment
Participants. The participants were eight right-handed, paid volunteers (four male), aged 24-45
years.
Stimuli & apparatus. The stimuli were the same as those used by Catmur, Walsh and Heyes
(2007), with the addition of a coloured circle (orange or purple), located equidistant between the
index and little fingers of the neutral hand, instructing the participant whether to respond with their
index or little finger. The left hand stimuli were created by reflecting the right hand stimuli in the
y-axis.
Theta burst rTMS was delivered at 80 % of each participant’s resting motor threshold (rMT; see
Rossini et al., 1994) via a 70-mm figure of eight coil connected to a Magstim Super Rapid machine
(The Magstim Company Ltd., Whitland, UK). The two stimulation sites (see Figure S1) were
located using a frameless stereotaxy system (BrainsightTM, Rogue Research Inc., Montreal,
Canada). rMT and RTs were measured using the same apparatus and procedure as Catmur et al.
(2007).
Two rTMS conditions and a baseline non-rTMS condition were used. rTMS was administered to
the left IFG, and also to the right PPC, to control for possible non-site-specific effects of rTMS. The
left IFG site was selected on the basis of the coordinates used by Pobric and Hamilton (2006). The
parietal control site was chosen to be posterior to areas in inferior parietal cortex that may be part of
the mirror system, and coordinates were based on those of Muggleton et al. (2006).
Figure S1. rTMS sites. Left: left IFG (Talairach co-ordinates -42.5, 11.6, 19.9); right: right PPC
(42, -58, 52).
Procedure. The experiment was carried out in two sessions, separated by at least 24 hours. Only
one site was stimulated in each session. Order of stimulation (IFG or PPC in the first session) was
counterbalanced between participants. Each session comprised the following stages: rTMS site
localisation; determination of rMT; practice and two baseline blocks of the automatic imitation task;
theta burst stimulation; four blocks of the automatic imitation task.
For each session, 300 TMS pulses were given in a continuous theta burst protocol. This consisted of
three pulses at 50 Hz, repeated every 200 ms for 20 s (Huang et al., 2005). Prior to the 300 pulses,
one second of theta burst stimulation was given (15 pulses), in order to acquaint the participant with
the sensation produced by the stimulation. Following the 20 s train, participants waited five minutes
after stimulation before commencing the automatic imitation task, since maximal inhibitory effects
of theta burst stimulation appear to occur at approximately seven to 14 minutes after stimulation
(Huang et al., 2005).
In the automatic imitation task, participants were instructed to respond as quickly as possible to the
coloured circle by making an abduction movement of the index finger or of the little finger.
Responses were measured using electromyography (see Catmur et al., 2007, for details). The
stimulus-response mappings (orange > index finger, purple > little finger, or vice versa), were
counterbalanced between participants.
Behavioural follow-up experiment
Participants. Eight right-handed, paid volunteers (one male), aged 20-29 years, participated. None
had participated in the previous experiment.
Stimuli. The stimuli were identical to those used in the previous experiment, with the exception that
the irrelevant movement stimulus was presented simultaneous with or 40 ms after the onset of the
discriminative stimulus.
Procedure. The procedure was equivalent to the baseline blocks of the previous experiment. The
video of the still hand was presented for 800 ms, after which time the discriminative stimulus was
presented. The irrelevant movement stimulus was then presented either simultaneous with or 40 ms
after the onset of the discriminative stimulus. Thus, the irrelevant movement stimulus could appear
at the same time as, or shortly after the discriminative stimulus. Trials, consisting of factorial
combination of trial type (spatially compatible, imitatively compatible; spatially compatible,
imitatively incompatible; spatially incompatible, imitatively compatible; spatially incompatible,
imitatively incompatible) and offset (0 ms, 40 ms), were presented in a random order.
Supplementary References
Catmur, C., Walsh, V., & Heyes, C. 2007. Sensorimotor learning configures the human mirror
system. Curr. Biol. 17, 1527-1531.
Huang, Y. Z., Edwards, M. J., Rounis, E., Bhatia, K. P., & Rothwell, J. C. 2005. Theta burst
stimulation of the human motor cortex. Neuron 45, 201-206.
Muggleton, N. G., Postma, P., Moutsopoulou, K., Nimmo-Smith, I., Marcel, A., & Walsh, V. 2006.
TMS over right posterior parietal cortex induces neglect in a scene-based frame of reference.
Neuropsychologia 44, 1222-1229.
Pobric, G. & Hamilton, A. F. 2006. Action understanding requires the left inferior frontal cortex.
Curr. Biol. 16, 524-529.
Rossini, P. M., Barker, A. T., Berardelli, A., Caramia, M. D., Caruso, G., Cracco, R. Q. et al. 1994.
Non-invasive electrical and magnetic stimulation of the brain, spinal cord and roots: basic principles
and procedures for routine clinical application. Report of an IFCN committee. Electroencephalogr.
Clin. Neurophysiol. 91, 79-92.