Effect of transcranial magnetic stimulation (TMS) on the planning and execution of imitative and complementary actions

In daily life humans often imitate the actions of other people. Imitation is
important for a number of processes including language acquisition, learning
of new motor plans and engaging in social situations [1]. For these reasons,
imitation has received much attention from the scientific community. When two
people have to carry out a cooperative task, imitation seems to be less
important. In these cases, achieving the goal of the action often depends on
the execution of a complementary action. For example, in order to take a mug
from someone you must often perform a different grip than you observe (i.e. if
someone hands it to you holding the ear, you must grip the body and vice
versa).

We recently conducted a fMRI experiment in which we compared brain areas
activated during the preparation of imitative and complementary actions [2].
The right inferior frontal gyrus (rIFG, pars opercularis) was significantly
more active during preparation of the complementary as compared to the
imitative actions. The goal van the present experiment is to directly test
whether or not the inferior frontal gyrus is necessary for the planning and
execution of complemplementary actions. In order to test this hypothesis we
will use a combined fMRI/TMS approach.

The study will take place over two days. On the first day we will take a 3-D
scan of the brain using fMRI. Participants will also perform the experimental
task (same as used for the TMS experient) while functional images area
collected. The fMRI portion will take approximately 45 minutes. The results
from the fMRI task will be used to determine more precisely the location within
the IFG that will be later stimulated (see the attached project sheet for
approval of the fMRI portion). Approximately two weeks after acquisition of
the fMRI data, participants will take part in the TMS portion of the experiment.

For the TMS portion, we will use the same basic task as in the fMRI version.
We will assess the effect of erTMS of IFG on imitation and complementary
actions using four experimental conditions. First, we will establish the motor
threshhold. Based on these results we will establish the stimulation strength
for that individual. Following this initial step, we will conduct the main TMS
experiment. Participants will be given detailed instructions and allowed a
brief practice period prior to the beginning of each of the experimental
blocks.

In order to disturb the activity of the three stimulation locations (rIFG,
lIFG, OCC) erTMS (maximum of three pulses per trial) will be applied. During
erTMS sessions three brain areas (locations) will be stimulated in a randomized
order.

In this study erTMS method will be used, and the maximum number of pulses per
trial will be three. The total number of magnetic pulses each subject will
receive is 1440 (480 per location), which fits within the TMS guidlines. In the
past, use of such parameters has never led to any side effects. There are no
known benefits to participating in this experiment.