Tempo-spatial discrimination is lower for noxious stimuli than for innocuous stimuli

• Published in: Pain (Amsterdam) Vol. 159; no. 2; pp. 393 - 401
• Main Authors: Frahm, Ken Steffen, Mørch, Carsten Dahl, Andersen, Ole Kæseler
• Format: Journal Article
• Language: English
• Published: United States Wolters Kluwer 01.02.2018
• Subjects: Adult; Discrimination, Psychological - physiology; Female; Humans; Lasers - adverse effects; Linear Models; Male; Pain - physiopathology; Pain Threshold - physiology; Physical Stimulation - adverse effects; Touch - physiology; Young Adult
• ISSN: 0304-3959; 1872-6623; 1872-6623
• DOI: 10.1097/j.pain.0000000000001095

The exteroceptive sensory system is responsible for sensing external stimuli in relation to time and space. The aim of this study was to investigate the tempo-spatial properties of the exteroceptive system using painful laser heat and nonpainful mechanical touch stimulation. Thirteen healthy subjects were stimulated on the volar forearm using 2 paradigms: a continuous stimulation along a line on the skin and a 2-point stimulation. The line stimulations were delivered in both the distal and proximal direction with lengths of 25, 50, 75, and 100 mm. The 2-point stimulations were assessed by simultaneous stimuli at a point-to-point distance ranging from 10 to 100 mm, in steps of 10 mm. The subjects reported the intensity (0-10 numeric rating scale, 3: pain threshold) and either direction (line stimuli) or number of perceived points (2-point stimuli). All mechanical line stimulations were reported correctly, ie, a directional discrimination threshold of less than 25 mm. For painful laser line stimulation, the directional discrimination threshold was 68.5 and 70.2 mm for distally and proximally directed stimuli, respectively. The 2-point discrimination threshold for painful laser stimulation (67.9 mm) was higher than for the mechanical stimulation (34.5 mm). Numeric rating scale increased both with line length and distance between the 2 points (linear mixed model, P < 0.001). The findings indicate that the tempo-spatial acuity of the exteroceptive system is lower for noxious stimuli than for innocuous stimuli. This is possible due to the larger receptive fields of nociceptive neurons and/or less lateral inhibition.