TMS and the temporal dynamics of word production

In 2004, Indefrey and Levelt proposed a comprehensive spatial and temporal
neural model of word production. The model (2004) outlines candidate regions in
the word production process as well as their functional time windows. More
recently, Indefrey (2011) update the existing model, giving the following
processing stages: conceptually driven lexical retrieval in the left mid MTG
from 200-275ms after picture onset; phonological code retrieval in the left
posterior MTG/STG from 275-355ms after picture onset; phonological encoding
(syllabification) in the left posterior IFG (pars opercularis) from 355-455ms
(duration varies with number of syllables); phonetic encoding and articulation
in bilateral inferior motor cortices from 455- 600ms after picture onset;
finally self-monitoring takes place in bilateral STG.
An online TMS picture naming study by Schuhmann et al. (2012) stimulated
the LIFG, mMTG and pSTG, during different time-windows after picture onset.
They found that LIFG activity is functionally relevant at an earlier
time-window (300ms) and that stimulating pSTG shows no effect in earlier time
windows for phonological code retrieval. The current experiment wishes to
address these issues by replicating the Schuhmann et al. (2012) study while 1)
manipulating word length in order to manipulate the functional time window of
LIFG and 2) stimulating pMTG to disrupt phonological code retrieval, as opposed
to mMTG.

Our objective is to disrupt neural activity in left inferior frontal gyrus
(LIFG), left posterior middle temporal gyrus (pMTG), and left posterior
superior temporal gyrus (pSTG) during different time-windows after picture
onset in order to determine the functional relevance of each brain area
throughout the word production process.

In this study participants will undergo a picture naming task. Triple pulse
transcranial magnetic stimulation (tpTMS) will be applied to three stimulation
sites in the left hemisphere: inferior frontal gyrus (IFG), left posterior
middle temporal gyrus (pMTG) & posterior superior temporal gyrus (pSTG). During
the task participants will receive a tpTMS stimulation in one of the three
stimulation sites, at one of five time-windows following picture onset.

Each participant will receive no direct benefit from participating in the
study, but will receive a compensatory (financial) incentive. Transcranial
magnetic stimulation (TMS) is a widely used non-invasive brain stimulation
technique, based on the principle of electromagnetic induction. During
stimulation the participant will likely hear the clicks of the TMS pulses and
experience stimulation of nerves and muscles of the head. The most common side
effect is a light transient headache (2-4% occurrence). A severe headache is
uncommon (0.3-0.5% occurrence). In TMS studies of patient populations (e.g.
epilepsy) or that exceeded the standard protocols (e.g. in intensity or
frequency) epileptic seizures have been reported in rare cases. In the current
study all participants will be stimulated with protocols that fall within the
safety guidelines. All subjects are screened for their relevant medical history
and other TMS safety aspects (e.g. presence of metal parts in the head). In
summary, because the risk and burden associated with participation can be
considered negligible-to-minimal, we do not expect serious adverse events
during the project. The noise in the fMRI scanner, and lying in a small space,
may lead to discomfort in some subjects.