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 poten tial at very late latencies, consistent with C-fiber transmission velo cities, 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) we re recorded from 30 electrodes covering the entire scalp. Data from th e 3 stimulus conditions (approximately 60 trials per condition per sub ject) were compared using the frequency domain technique of complex de modulation applied to single trial data. Subjects were 14 normal right -handed male human volunteers, aged 19-36 years. Results: Using descri ptive probability mapping, pain versus strong non-pain differences wer e found in grand average data as well as in 8 of 14 subjects, consisti ng of greater low-frequency power at latencies from 700 to 1100 ms at electrodes near the contralateral central sulcus and at the vertex. Co nclusions: There are topographically focal, pain versus non-pain diffe rences in the 700-1100 ms latency range that can be seen using frequen cy-domain analytic techniques. These differences were not seen with tr aditional time domain analyses. They may be due to a C-fiber-related m echanism or to very late activity triggered by faster fibers. (C) 1998 Elsevier Science Ireland Ltd. All rights reserved.