The primary aim of this study was to compare and contrast fMRI spinal processing of nociceptive and motor signals in humans. We hypothesized that 1) the signal time course of the nociceptive and motor tasks would differ and 2) tonic pain and phasic pain would differ, as tonic pain activates both A-delta and C nociceptive fibers while phasic pain primarily activates A-delta fibers. Twelve volunteers consented to the study and were scanned in a 3T whole-body MRI system by GE, with an HD neurovascular array coil. Noxious stimuli were presented by a computer-controlled thermode placed on the thenar eminence of the hand. Tonic heat stimulus was a 48°C block. Phasic stimulus oscillated from 40°C to 48°C at 10°C/sec. Each subject participated in three, eight-minute blocks of functional scans: 1) thirty seconds of fist-clenching alternated with thirty seconds of rest, 2) thirty seconds of 48°C phasic stimulus alternated with thirty seconds of rest, and 3) thirty seconds of 48°C tonic stimulus alternated with thirty seconds of rest.

Preliminary data were analyzed in Brain Voyager at p=0.05. Because the hemodynamic response function (HRF) has not been well characterized in the spinal cord, we deconvolved a spinal HRF from the motor task and used that HRF for all analyses. Activity maps and signal time courses were generated from all three runs for each subject. In the fist-clenching task, activity was observed in the dorsal horn, possibly corresponding to sensory input from the palm. During both tonic and phasic pain, there was activity in the spinal areas of C5-C7. Event-related averages (ERAs) for the fist-clenching task increased and plateaued. ERAs for phasic pain were slower to peak. As compared to the tonic task, the phasic task showed increased BOLD percent change. These results are in concordance with electrophysiological recordings of nociceptive fibers in animals.