Classifi cation of the stimuli that elicit the sympathetic skin refl ex. Non-physiological, physiological and cognitive and emotional stimuli

Introduction: The sympathetic skin response is generated by a diversity of non-physiological, physiological, cognitive and emotional stimuli. The stimuli that induce the response seem to be disparate and unrelated. We propose a classifi cation of the stimuli that induce the electrodermal response and suggest a common physiological basis underlying the various stimuli. Subjects and methods: We studied twenty healthy subjects in whom the sympathetic skin response was induced with: 1) a cough; 2) a sudden blank noise; 3) eye opening; and 4) muscle contraction. The electrodermal response was obtained ten times in each subject with each stimulus. The stimulus was given one minute apart. The respiratory, the acoustic, the eye opening and the muscle contraction stimuli were recorded in the traces of all subjects. We also obtained the response at least three times in each subject during the moment of standing, sighs, sudden inspirations, talking, unexpected tactile stimulation, verbal instructions, mental calculations, and during the cold face test. Results: The response was readily obtained with cough, noise, eye opening and muscle contraction in all normal subjects. The amplitude of the response varied from trial to trial and from subject to subject. We did not give repetitive stimulation to habituate the response. Somnolence was the most common cause of an absent response. Sighs were the most common cause of a seemingly spontaneous response. Laughter and mental calculation gave a large and long lasting response. Discussion: The proposed classifi cation of the sympathetic skin response in non-physiological, physiological and cognitive and emotional seem to have some heuristic value. The sympathetic skin response seems to be part of a generalized mechanism of arousal and attention in which there is sympathetic activation of the eccrine skin glands of the skin. The sympathetic skin response is a complex response that acquires a physiological meaning when seen as a part of a generalized sympathetic activation. The sympathetic skin response should always be recorded with respiratory movements. Noise, eye opening, muscle contractions, verbal instructions and somnolence are confounding factors that should be monitored.