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Human cerebral potentials evoked by CO2 laser stimuli causing pain
Experimental Brain Research
|January 1, 1987
Summary
Brief radiant heat pulses activate C-fibers, revealing two pain sensations and distinct evoked cerebral potentials (EPs). Blocking A-fibers isolates the second pain and reveals ultralate EPs, suggesting convergence of neural inputs.
Area of Science:
- Neuroscience
- Human Physiology
- Pain Perception
Background:
- Slowly conducting afferents in hairy skin transmit pain signals.
- C-fiber and A-fiber activation can lead to distinct sensory experiences and evoked potentials.
Purpose of the Study:
- To investigate the characteristics of C-fiber activation using brief radiant heat pulses.
- To differentiate the evoked cerebral potentials (EPs) associated with A-fiber and C-fiber activity.
- To explore the nature of second pain sensation and its corresponding EPs.
Main Methods:
- CO2 laser pulses applied to hairy skin in humans.
- Preferential A-fiber block induced by pressure on the radial nerve.
- Recording of stimulus estimation, evoked cerebral potentials (EPs), reaction times, and autonomic responses.
- Analysis using conventional averaging and latency-corrected averaging with a modified Woody filter.
Main Results:
- A double pain sensation (sharp followed by burning) was observed with intact nerves.
- A-fiber block isolated the second, burning pain sensation.
- Late EPs (N240/P370) were recorded with intact nerves.
- An ultralate EP (beyond 1000 ms) was observed under A-fiber block, with greater latency jitter.
- Latency-corrected averaging revealed an ultralate EP (N1050/P1250) similar in shape to the late EP.
Conclusions:
- Both late and ultralate EPs may represent secondary responses to afferent input converging onto neural centers.
- Convergence of myelinated (A) and unmyelinated (C) fibers might explain the observed EPs.
- Mechanisms like habituation and attention may influence the reliable detection of ultralate EPs without nerve blocks.