Very late pain-related activity identified with topographically mapped frequency domain analysis of evoked potentials.
OBJECTIVE
To identify low-frequency activity in the pain-evoked potential at very late latencies, consistent with C-fiber transmission velocities.


METHODS
Brief (1 ms) painful (intracutaneous) and two levels of non-painful (mild and strong) electrical pulses were applied to the index and middle fingers of the left hand. Evoked potentials (EPs) were recorded from 30 electrodes covering the entire scalp. Data from the 3 stimulus conditions (approximately 60 trials per condition per subject) were compared using the frequency domain technique of complex demodulation applied to single trial data. Subjects were 14 normal right-handed male human volunteers, aged 19-36 years.


RESULTS
Using descriptive probability mapping, pain versus strong non-pain differences were found in grand average data as well as in 8 of 14 subjects, consisting of greater low-frequency power at latencies from 700 to 1100 ms at electrodes near the contralateral central sulcus and at the vertex.


CONCLUSIONS
There are topographically focal, pain versus non-pain differences in the 700-1100 ms latency range that can be seen using frequency-domain analytic techniques. These differences were not seen with traditional time domain analyses. They may be due to a C-fiber-related mechanism or to very late activity triggered by faster fibers.
Department of Anesthesia, University of California, San Francisco 94143-0648, USA. dbecker@itsa.ucsf.edu
D E
DE
Becker
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RS
Noss
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Fein
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CD
Yingling
D000328:Adult; D001921:Brain / Q000503:physiopathology*; D001931:Brain Mapping; D004558:Electric Stimulation; D005071:Evoked Potentials / Q000502:physiology*; D005385:Fingers / Q000502:physiology; D006801:Humans; D008297:Male; D010146:Pain / Q000503:physiopathology*; D011336:Probability; D011930:Reaction Time / Q000502:physiology