Wednesday, March 13, 2019

Assessment of experimental orofacial pain, pleasantness and unpleasantness via standardised psychophysical testing

Abstract

Background

Somatosensory assessment within the orofacial region may be performed using highly standardised quantitative sensory testing (QST). However, the function of the C tactile (CT) afferent, a nerve fibre linked to the perception of pleasant touch, is usually not evaluated. Furthermore, the perception of unpleasantness is also rarely assessed; a dimension not only limited to a painful experience. Therefore, the primary aim was to apply standardised QST stimuli as well as standardised pleasant stimuli and evaluate their potential capacity for evocation of perceived pain, pleasant and unpleasant sensations in the facial region.

Methods

Twenty‐one female participants underwent QST as per the protocol derived from the German Research Network on Neuropathic Pain. For the first time, two modified protocols were used to investigate stimuli for perceived pleasantness and unpleasantness.

Results

Thermal stimuli provided separate thresholds for each sensation. From certain mechanical stimuli (e.g. vibration), overlap between the perceived sensations of pleasantness and unpleasantness were identified. It was not possible to evoke only an unpleasant sensation without a painful contribution, and both these sensations increased significantly when utilising an increasing pinprick force (p < 0.011). Between dynamic stimuli, the brush was rated as significantly more pleasant than the cotton wool tip (p = 0.015). A quadratic model provided the best fit for velocity against mean pleasantness ratings (R2 = 0.62 ± 0.08), supporting previous CT afferent literature to some extent.

Conclusion

Stimuli were generally not isolated to one sensation, highlighting the multidimensional construct of stimulus perception, and the need for scales to capture this.

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