Selective averaging of argon laser induced pre-pain and pain related cortical responses.

The argon laser was found to be suitable for pre-pain and pain stimulation. The visible (488 and 515 nm) argon laser light penetrates the skin and is absorbed by melanin and haemoglobin. Argon laser stimuli of different intensities were perceived differently, and could be classified into 3 pre-pain and 3 pain classes. The pre-pain sensations were either perceived as warmth, weak pin prick, or weak pin prick followed by warmth. The pain sensations were perceived as painful pin pricks of different intensities. Single cortical responses to argon laser stimuli were averaged selectively, according to this perceptual classification, and characteristic pre-pain and pain related cortical responses were recorded. The sensation of warmth was related to a late cortical deflection, 700-800 ms after stimulus onset, whereas the pin prick related response appeared with a latency of 300-400 ms. Pre-pain related responses were only recorded when selective averaging according to perception was used. The amplitude of the selectively averaged pain related cortical responses correlated with the subjective sensation of pain. Selective averaging of pre-pain and pain related single responses may prove useful in studying the cortical projection of different perceptions or modality patterns, and to investigate the function of the thermal and nociceptive pathways and their interactions.