Phasic skin conductance activity and motion sickness

Sweating is commonly associated with motion sickness. Previous studies have attempted to relate sweating or the associated electrodermal activity to the degree of motion sickness symptoms. This study was aimed at improving methodology by study of 1) recording site--palmar finger versus forehead; and 2) signal analysis--tonic skin conductance level (SCL) versus phasic skin conductance responses (SCRs). Eleven subjects were exposed to a cross-coupled motion challenge, produced by repeated head movements (16 per minute) during rotation around the Earth vertical axis in which rotational velocity was incremented on a staircase profile from 3 degrees to 99 degrees.s-1 to an end point of moderate nausea. Six subjects underwent additional control conditions of rotation only and head movements only. A group of 12 subjects underwent sessions of vertical and horizontal sinusoidal linear motion through the head z-axis at 0.3 Hz, 1.8 ms-2 rms. Sweating responses were recorded in a further three subjects by mass spectrometry for water vapor from the skin using a dry N2 gas flow method. Phasic skin conductance activity at the forehead site provided the best correlate of motion sickness onset and recovery. Other combinations of signal analysis or recording site were less useful.