Effect of limb pain on scalp tenderness during motion sickness

Researcher Lone Knudsen

Supervisors Professor Peter Drummond

Date: 11th June, 2010

A disruption of central pain control may be involved in the development of scalp tenderness during motion sickness. The aim of this study was to investigate the effect of limb pain on sensitivity to noxious stimulation on each side of the forehead during motion sickness. Motion sickness was induced by optokinetic stimulation (i.e., by placing the head inside a rotating drum with black and white vertical stripes). Eighty-five healthy volunteers were subjected to a cold pressor (CP) task of the hand on two occasions. On one of these occasions, the CP was preceded by optokinetic stimulation. Pressure-pain thresholds and ratings of sharpness were obtained from each side of the forehead before and after each stimulus. On its own, the CP decreased forehead sensitivity to sharpness and inhibited increased sensitivity to pressure-pain in pain sensitive individuals suggesting involvement of inhibitory pain control mechanisms such as diffuse noxious inhibitory controls (DNIC) and stress-induced analgesia (SIA). Scalp tenderness to pressure and sharpness developed during residual motion sickness, but bilateral forehead analgesia both to pressure and sharpness emerged to the concurrent CP. These findings suggest that DNIC and SIA remained intact during residual motion sickness. As the CP induced greater pain in pain insensitive individuals during residual motion sickness, a facilitatory mechanism rather than disinhibition may be involved in the development of scalp tenderness during motion sickness.