LONG-TERM DEPRESSION OF PAIN: DO STIMULATION PARAMETERS MATTER?

Frequent pain attacks may induce long-term potentiation of nociceptive processing as a prerequisite for chronic pain. Under experimental conditions, potentiated nociception recovers to baseline by electrical low frequency stimulation (LFS) in rodents. Thus, LFS may be a potential treatment in order to weaken or even erase pain memory. The present study addressed the efficacy of different stimulation parameters on nociception and pain in man. Electrophysiological and psychophysical experiments were performed in 29 healthy volunteers (16 female, 13 male; 20 to 53 years). Painful electrical test (0.125 Hz) and conditioning stimuli (LFS: 0.5, 1, or 2 Hz; 300, 600, or 1200 pulses; 1×IP, 2×IP, or 4×IP; IP=pain threshold) were applied to the right hand dorsum by a concentric electrode. This special designed electrode allows preferential activation of nociceptive A‰ fibres. Somatosensory evoked cortical vertex potentials (SEP) were recorded via EEG. Volunteers gave test stimulus intensity ratings (0 to 100). Inhibitory effects of LFS depend on stimulus frequency, number of pulses and stimulation intensity. Stimulation protocol with 1 Hz, 1200 pulses and 4×IP induced the strongest sustained reduction of SEP and pain rating (-47.1% SEP, -43.8% Pain, p<0.001). Established LTD after single LFS was amplified (-54.6% SEP, -47.7% Pain, p<0.01) by an additional second LFS. Our results indicate that electrical LFS is able to inhibit pain and nociceptive processing for at least one hour in healthy volunteers. Existence of LTD and its amplification by repetitive LFS may qualify this approach for neuromodulatory treatment of chronic pain.