Localization of electroctutaneous stimuli.

Rationale:

The body schema is the unconscious awareness of our body, which is fed by various sensory modalities. Various disorders have been hypothesized to be reflected in this awareness. When people report the location of a cutaneous stimulus they refer to their body schema, therefore studying the reported locations of stimuli on the skin may provide information about this schema. Although tactile localization has been studied repeatedly, many factors which may influence spatial perception of touch remain unidentified, which impedes interpretation of the results. Localization data is known to have both systematic and stochastic errors when comparing it to the actual stimulus sites. The systematic component differs between subjects. It is at present unknown whether the systematic component is a trait of a subject or whether it changes when repeating the same measurement at another time. Also, the effect of stimulus strength and duration on the stochastic and systematic components is unkown. Another unknown is whether the spatial perception of touch and nociception are the same. Finally, the study of spatial perception would benefit from a critical evaluation about the statistical methods used for analyzing the data.



Objective:

In this study we address the influence of stimulus strength, modality and duration on reported locations of cutaneous stimuli. In addition, we assess the reproducibility of these reports and test whether we can improve the analysis of localizations by identifying clusters in this data. All stimuli will be applied using electric stimulation on the skin.



Study design:

The study consists of 5 series of experiments which use electric stimuli of tactile afferents:

1. Reproducibility and clustering study consisting of a pilot phase (5 subjects, 2 experiments each) and final series (25 subjects, 2 experiments each);

2. Influence of stimulus strength on tactile localization (45 subjects);

3. Effect of stimulus frequency and duration on tactile localization with a pilot stage (5 subjects) and final stage (40 subjects);

4. The effect of gaze direction on clustering in tactile localization with a pilot stage (max 5 subjects) and final stage (15 subjects). Experiment series 5 also includes nociceptive electric stimuli and will compare the localization of tactile and nociceptive stimuli (15 subjects).



Study population:

Healthy, right-handed volunteers, aged between 18-30 years.



Main study parameters/endpoints:

Main parameters of the various experiment series are the following stimulus parameters: Location, strength, frequency, duration and modality. In one experiment, gaze direction of the subject will be varied. The outcome measures are reported location, which will be analysed in respect to variance and mean per site as well as clustering behaviour.



Nature and extent of the burden and risks associated with participation, benefit and group relatedness:

Each experiment will last approximately 1.5-2 hours depending on the experiment. The first hour consists of preparations; the remainder is taken up by the main experiment. In 4/5 experiments all stimuli feel as a dull tap. In the tactile/nociceptive comparison experiment half of the stimuli will feel as a light pinprick. There are no risks involved in participating in these experiments. The needle electrodes used in experiment series 5 can cause mild skin irritation which disappears within half an hour after removal of the electrodes.

Stimulus strength, duration and modality influence the reported location of cutaneous stimuli.

Each experiment lasts 2 hours.

Subjects receive electrocutaneous stimulati at 8 sites on their forearm. The electrode positions are hidden for the subjects by a tablet screen which presents a picture of the arm without electrodes. Subjects report the perceived location of the stimuli by tapping on this screen.
All experiments are performed on healty subject. All analyses will be within subject, no comparison between groups is made. Experiments last approximately 2 hours, of which 1 hour is preperation and 1 hour the actual localization task.