The role of the parietal cortex in re-orienting to emotional stimuli: a single-pulse TMS study

Emotional stimuli, such as threatening stimuli affect attention selection. It
is still not clear what the underlying neural mechanisms are of this
attentional modulation. In the present study we will investigate the role of
the right posterior parietal cortex ( PPC), an area important in shifting
attention to task-relevant stimuli (reorienting ). In the current study ,
participants perform a spatial cueing task while the right PPC is stimulated by
single pulse transcranial magnetic stimulation (TMS). In the cueing task
attention is first captured by a neutral peripheral sudden onset cue presented
to the left or right of the fixation point .Subsequently, participants must
respond to a threatening or non-threatening target presented at the same
location (valid) or at the opposite location (invalid) of the cue. If the
target appears on the opposite location, attention should be re-oriented to
this location. After the onset of the target , we will administer a single
pulse TMS to intefere with the re-orienting proces. A previous study ( Chambers
et al ., 2004) has shown that PPC is crucial in reorienting to task relevant
(emotionally neutral) stimuli. Chamber et al. found that single pulse TMS
interfered with reorienting to the target at two different points in time (two
time- windows); a time- window corresponding to rapid subcortical processing
and a time- window corresponding to slower cortical processing. To investigate
whether reorienting to threatening stimuli is processed more quickly than
non-threatening stimuli, we will use the set-up of Chamber et al , (2004) with
the addition of a threatening (CS +) or non-threatening target (CS-). In order
to investigate the temporal characteristics of re-orienting, the timing of the
pulse will be systematically varied between trials. We measure the manual
responses (percentage of correct and reaction time) to the target stimulus in
order to determine when the right- PPC is involved in the re - orienting to
threatening stimuli. The results will improve our knowledge and understanding
of the underlying mechanisms of emotional modulation of attention. In addition,
the results will also contribute to methods that can be developed for the
prevention and treatment of anxiety disorders , for instance by means of
attentional bias modification .

Primary objective: The most important question this study wants to answer is
when the right posterior parietal cortex (PPC) , which is known to be involved
in re- orienting to task-relevant stimuli , is involved in re - orienting to
threatening stimuli. Results from the study provide insight into the underlying
neural processes of emotional modulation of attention, more specifically the
timing of the process . By measuring manual responses to invalid targets in a
spatial cueing task with threatening and non -threatening targets, we can
investigate when re-orienting occurs and what the possible underlying neural
correlates of the process might be. We anticipate that single pulse TMS
inteferes with reorienting to threatening stimuli only in the first time window
and not in the second time- window .
Secondary objective (s ) : In addition to our primary objective, we will
investigate a possible correlation between the degree of
anxiety as measured by the VAS and the STAI-T with re - orienting, as indexed
by the difference in performance on the invalid CS+ target and CS- target.

The study takes place in the Donders Centre for Cognitive Neuroimaging ( DCCN )
as a within-subject experiment with healthy, adult volunteers. The study
consists of two experimental sessions. In the experimental sessions, the
participants will first practice the task. Subsequently, by means of a work-up
procedure the participant determines the intensity of the electrodermal
stimulation after which the fear-conditioning procedure is peerformed.
Immediately thereafter the experiment begins. During the experiment, a tsingle
-pulse is administered to the right PPC on each trial. The timing of this
pulse, with respect to the target onset (Target - TMS SOA), is systematically
varied. A session consists of 10 blocks of each fifty trials, between the
blocks participants can take a pause. In total, the experiment takes no longer
than half an hour (including breaks). In the second session, participants are
asked to complete the questionnaire ( STAI- T). In total, a session lasts no
longer than 60 minutes.

TMS can cause a mild headache during stimulation. For the assessment of risks
and charges related to transcranial magnetic stimulation in this study we refer
to section 5.2 of the approved Standard Use Procedure for Non-invasive
stimulation of Brains ( v. 2.1., CMO Nr. 2013/245) at the Donders Institute for
Brains , Knowledge and Behaviour.
The electrodermal stimulus is unpleasant but not painful. For the assessment of
risks and charges related to electrodermal stimulation in this study we refer
to section 8.3.1 of the approved Research Protocol Imaging Human Cognition (v
1.0., CMO 2014/288) .