Modulation of Somatosensory Stimulus Evoked Potentials and Pain by Self-Touch

We have recently shown that acute pain can be reduced by multisensory
integration through self-touch, which provides proprioceptive, thermal, and
tactile input forming a coherent body representation (Schütz-Bosbach, Musil, &
Haggard, 2009; Ehrsson, Holmes, & Passingham, 2005; Kammers, de Vignemont, &
Haggard, 2010). However, the question remains what the precise underlying brain
mechanism of this reduction in perceived pain is. Consequently, in the present
study we want to expand this behavioural finding by looking at the precise
brain mechanism underlying self-touch. The primary prediction is that the
processing of afferent peripheral somatosensory and pain signals to the brain
is altered when one is experiencing self-touch versus when one is touching
something or someone else.
In Experiment 1 we will use light shocks to simulate tactile stimulation and
look at SEPs during self-touch or external touch (touching the experimenter)
while in Experiment 2 we will use (an illusion of) pain and look at the ERPs
during self-touch versus external touch. For the induction of pain we will use
the well-known thermal grill illusion (TGI) (Craig & Bushnell, 1994). To induce
the TGI the participant's index and ring fingers of each hand will be immersed
in mild warm water while the middle finger will be slightly cooled in mild cool
water. Immediately after induction of 50 seconds, the fingers will be removed
from the water and pressed either against each other or on the hands of the
experimenter. For both the SEPs (Exp 1) and the ERPs (Exp 2) the EEG signals
for self-touch versus external touch will be compared.

The main objective of this study is to investigate the brain mechanisms
underlying the modulatory effect of self-touch on afferent somatosensory (Exp
1) and pain signals (Exp 2).

The study consists of two experiments, the first of which investigates
somatosensation and the second of which investigates pain processing. Both
experiments are within-subjects designs. Different participants will take part
in the two experiments. During each experiment brain activity is monitored in
the participant by means of electro-encephalography, forming the main set of
dependent measures.
All participants visit the laboratory once for testing which will take about 2
hours.

This study is non-therapeutical, uses no medicinal products, no invasive
techniques, no interventions and will not include minor and/or incapacitated
adults or dependent subjects. Due to the design of this study (see section 3
for details), no medical risks are associated with participation. Discomfort of
the participation by the SEP stimulation is minimal, and several studies in our
lab showed no medical or psychological risks associated. The risks of this
project are therefore regarded as minimal.