Attentional interference by itch and pain

Of the general population, approximately 14% suffer from chronic itch and
approximately 20% suffer from chronic pain, which both can severely affect
patients* quality of life. For pain, it has been shown that attentional
processes can be dysregulated, mainly difficulty disengaging from pain, as
shown by studies using behavioural attention tasks. This can result in
attentional interference in daily activities. Additionally, neurophysiological
studies also indicate that the alpha-desynchronization patterns, a
neurophysiological measure of attentional processing, as measured by for
example electroencephalography (EEG), are altered in patients with chronic
pain. For itch, attentional processes have barely been investigated. Our
recently developed somatosensory attention task (SAT) with somatosensory itch
and pain inductions allows to quantify the extent to which itch and pain
interfere with task execution, and thereby gives insight into the attentional
processes associated with itch and pain (e.g., attentional disengagement).
However, this task needs to be optimized further as in previous versions of the
SAT the targeted intensity of itch and pain was not reached in a considerable
proportion of participants and extensive randomization of targets limited the
potential to analyse attentional processing over the time course of a stimulus.
Moreover, neurophysiological correlates of attentional processing have not been
investigated so far with respect to itch and only sparsely for pain. Such
information about attentional interference by itch and pain in healthy
participants is necessary before these processes are to be investigated more
thoroughly in patients with chronic itch or pain.

The primary objectives are to investigate attentional interference by
somatosensory itch and pain stimuli in healthy subjects, both on a behavioural
(SAT) level and a neurophysiological level (EEG alpha-desynchronization).

Secondary objectives include investigating whether itch or pain attract
attention to its spatial location and it will be explored whether this
attention allocation varies over the time course of a stimulus. Moreover,
neurophysiologically the pattern of alpha-oscillations during the time course
of the itch and pain stimuli, irrespective of the SAT, will be investigated.
The pattern of alpha-oscillations will also be explored during the SAT if the
EEG-signal allows to do so (e.g., the signal is not contaminated by artefacts
due to the visual target stimuli within the SAT).

Other objectives include investigating attentional processing of itch pictures,
using a previously developed dot-probe task, and one*s general ability to
disengage attention (irrespective of itch and pain) using the Flanker task.
Additionally, associations between the outcomes of the behavioural and
neurophysiological attention tasks and individual characteristics related to
attention will be explored.

This is an experimental study including healthy subjects in a within-subjects
design. The study consists of two parts. First, participants fill out
self-report questionnaires at home (ca. 15 mins). Second, participants visit
the laboratory where the behavioural attention tasks will be administered (ca.
3 h). The experiment includes breaks.

General procedure: Potential participants receive written information about the
study. They are informed about the study procedures and they are informed that
the study investigates perception of itch and pain. They are not explicitly
informed about the goal of investigating attentional mechanisms, as this
knowledge could influence study results. Prior to visiting the lab, potential
participants will fill out several screening questionnaires via an online
system (Qualtrics). Subsequently, eligible participants will make an
appointment for participation. The testing session will take place at the
Faculty of Social and Behavioural Sciences, Leiden University and will take
approximately 3 hours. After an explanation of the procedures and a brief check
of the in- and exclusion criteria, participants will be asked to sign the
informed consent form. First, a short general attentional interference task
will be employed; the flanker task. Afterwards, EEG electrodes will be applied
to the head of the participant, and EEG will be measured during rest, followed
by recordings during three different types of somatosensory stimuli: electrical
itch and pain stimuli and vibrotactile (pulsation) stimuli. Subsequently,
participants will conduct the SAT in which the three types of somatosensory
stimuli are applied. Thereafter, the electrodes for the somatosensory stimuli
will be removed. Lastly, participants will perform a short computerized
behavioural attention task: the dot-probe task for itch. After finishing the
measurements, electrodes for EEG will be removed.

No risks are known for the administration of the questionnaires, computer
tasks, pulsating tactors (as control condition) and EEG measures. Also for the
electrical stimulation, the safety of participants is guaranteed throughout the
entire experiment, as an apparatus qualified for clinical research will be
used, which continuously confines the amount of electrical transmission given
to the participant. The electrical stimulation does induce itch or pain for
short duration and can cause temporary redness of the skin. No direct benefits
are expected to be experienced by the participants.