Emotional modulation of attentional selection: A transcranial magnetic stimulation study

Emotional stimuli, such as threatening stimuli, are known to influence
attentional selection. However, how and when these stimuli modulate attentional
selection is not yet clear. In the current study, we will investigate the
influence of the right parietal cortex, involved in stimulus driven spatial
attention on attentional orienting to threatening stimuli. We will use offline
1-Hz repetitive transcranial magnetic stimulation (rTMS) to the parietal
cortex, which results in a transient disruption of cortical activity at the
stimulation site. Subsequently, participants will perform a visual search task
with irrelevant distractors that can either be threatening or non-threatening.
We will measure manual responses to the target stimulus in the presence and
absence of distractor to index attentional capture. The results will increase
our knowledge and insights in the mechanisms underlying emotional modulation of
attention. Moreover, the study will contribute to methods involved in the
prevention and treatment of anxiety disorders.

Primary Objective: The main question this study wants to address is whether the
right posterior parietal cortex, known to be involved in saliency detection and
stimulus driven orienting, is also involved in orienting to emotional stimuli,
such as threatening stimuli. We will index attentional capture by the
difference RT for distractor present minus absence trials. We expect to find
and interaction between TMS (sham rTMS, left rTMS and right rTMS) and
distractor type (threatening, non-threatening). For non-threatening distractors
we expect to find a difference between distractor present and absent trials
that persists with sham TMS and left rTMS and is reduced with right rTMS. For
threatening distractors, we expect that the difference RT persists across the
TMS conditions.
Secondary Objective(s): In addition to our primary objective, we expect to find
a correlation between the level of state anxiety as measured by ratings on the
VAS and attentional capture by threatening distractors as indexed by the
difference RT score between distractor present minus distractor absent.

The study is a sham controlled randomized cross-over design. Each participant
will complete an intake session of maximum 30 minutes on one day, followed by
three experimental sessions on three separate days of approximately 60 minutes.

During the intake session, explanation of experimental procedures, written
informed consent, standard health and safety-screening list is administered. In
addition, individual motor threshold (MT) from the left primary motor cortex
using the thumb movement visualization method will be measured to determine
stimulation intensity (Schutter & Van Honk, 2006).

In each experimental session, participants will first practice the task and
perform the fear-conditioning procedure as described in section 8.3 study
procedure. Subsequently, the will receive a 20-min 1-Hz train of pulses of
either sham rTMS (left or right sham TMS will be counterbalanced between
subjects), or rTMS to the left or to the right parietal cortex. Previous
studies have shown that these parameters transiently disrupt cortical activity
at the site of stimulation (e.g., see Hilgetag, Theoret & Pascual-Leone, 2001;
Mevorach, Humphreys, Shalev, 2005; Schutter et al., 2001; Van Honk et al.,
2002). The site of stimulation will be the same as that of Hodsoll et al., 2009
corresponding to points P3 (left parietal) and P4 (right parietal) on the 10-20
electroencephalography coordinate system. Stimulation intensity will be set at
10% below the resting motor threshold of each participant. Following the rTMS
stimulation, the participants will perform the task as described in study
procedure (section 8.3).

The research will take place at the Brain Stimulation Laboratory of the
Department of Experimental Psychology, Utrecht University.

There are no immediate benefits associated with the study. TMS might be
somewhat uncomfortable and may cause a mild headache during stimulation. When
TMS is applied at fast frequencies (>= 25 Hz) the risk for an insult increases.
However, given the currently proposed TMS parameters the likelihood of adverse
events, like nausea, dizziness or an insult is negligible (Please see also 7.2
Adverse and serious adverse events). Total duration of the study per
participants is no more than 1 hour. The loud sound is uncomfortable but given
the current parameters the likelihood of adverse events is negligible. The
volunteers will be paid for participation. They can withdraw from the study at
any given time. Given the very low risks of this study comparing to the
potentially large benefits, we regard this study legitimate and eligible.