NERVE-FIBER DISCHARGES, CEREBRAL POTENTIALS AND SENSATIONS INDUCED BY CO2-LASER STIMULATION

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  • 1 January 1984
    • journal article
    • research article
    • Vol. 3  (1) , 33-40
Abstract
Short radiant heat pulses, emitted by a high power CO2 laser, were used to investigate single nociceptor activity, cerebral potentials and concomitant sensations. Stimuli of 20 and 50 ms duration with different intensities were randomly applied to the hairy skin of the hand. Microelectroneurography was performed from the radial nerve at the wrist; 26 stable recordings were evaluated. Pre- and poststimulus EEG segments were recorded from vertex versus linked ear lobes. Sensation was assessed on an 8-step category scale, an adjective scale, and by reaction times. In some experiments in A-fibers block was applied in order to isolate C-fiber responses. Short heat stimuli activate C-units. In addition 1 of 2 identified A.delta.-units responded. None of the 15 A.beta.-units investigated was activated by the heat pulse. Short heat stimuli evoked cerebral potentials having a main vertex positive component at about 400 ms. These potentials were ascribed to A.delta.-fiber input. Laser induced pain consisted of an immediate stinging component, followed by a burning pain which often lasted several seconds. Reaction time to 1st pain ranged from 400-500 ms. Weak laser stimuli induced non-painful sensations mostly of tactile character. High correlations were found between the number of spikes elicited by a given stimulus and the intensity of the evoked sensation. Intensity discrimination, as evaluated by measures of Signal Detection Theory, was better in the peripheral C-units than in the subjective ratings. If conduction of A-fibers was blocked by pressure, A.delta.-related cerebral potential components vanished. Instead a vertex positivity at about 1260 ms emerged; its peak latency corresponded well to the prolonged reaction time of 1100-1900 ms. This ultralate evoked cerebral potential is supposed to be a correlate of C-fibers mediated 2nd pain.