Descending modulation of the nociceptive system has proven to be pronounced in healthy humans. The descending modulation can be activated by rather distinct methods such as strong tonic painful stimulation or changes in the cognitive state. The extent of descending modulation on spinal pain processing remains unclear. Therefore, we assessed simultaneous cognitive modulation of spinal and cortical processing of experimental pain.
Painful (1.7 × pain threshold (PT)) and non-painful (0.5 × PT) electrical stimulation was applied to the sole of the foot of 9 healthy subjects. Cortical activity was recorded by EEG from the vertex and the nociceptive withdrawal reflex (NWR) was recorded from the tibialis anterior muscle. Stimulations were applied during the Spatial Attention Task, where the subject was asked to indicate the direction of arrows presented in a computer screen, and when the subjects were relaxed. The subject was asked to rate the average pain intensity after 30 stimuli. A total of 240 stimuli were applied.
The amplitude of the EEG P100 (p < 0.001), P300 (p = 0.019) peaks, the pain intensity (p < 0.001) and the NWR (p < 0.05) were all significantly higher when noxious stimulation was applied than when non-noxious stimuli were applied. The spatial attention task did not significantly modulate the amplitude of the P100 (p = 0.083), the P300 (p = 0.804) peaks, and the pain intensity (p = 0.139), but the NWR were significantly lower during the Spatial Attention Task (p = 0.042).
The results indicated that attracting the attention of the subjects to a task of spatial discrimination evoked a descending modulation affecting nociceptive processing at the spinal level. Still pain perception and late components of the vertex EEG were not significantly altered by the spatial attention task.
© 2012 Scandinavian Association for the Study of Pain