Differential cerebral responses to aversive auditory arousal versus muscle pain: specific EEG patterns are associated with human pain processing.

The specificity of electroencephalogram (EEG) activity in relation to processing of human pain needs further elucidation. This study was designed to determine if nociceptive input and general arousal responses to external stimulation exert different effects on EEG activity. Continuous aversive auditory stimuli (90 dB for 2 min) and painful injection of hypertonic saline (5.8%, 0.2 ml) into the left brachioradialis muscle were administered to 12 male subjects during separate sessions in a counterbalanced design. Intensity, arousal and unpleasantness were assessed during the muscle pain and auditory stimulation using a visual analogue scale and arousal-affective scales. The EEG data (32 channels) was acquired before, during and after application of painful and aversive auditory stimuli. Aversive auditory stimulation and intramuscular injection of hypertonic saline induced similar degrees of arousal and unpleasantness associated with a similarity of intensity of sensation of pain and auditory sensation. However, muscle pain induced a significant decrease of alpha-1 activity (8-14 Hz) at T6, PC2, PC6, Pz, P4, O2 and POz sites compared to the baseline, but aversive auditory stimulation did not produce any significant changes in alpha-1 activity compared to baseline. The alpha-1 EEG powers at P3, Pz, P4, PC1, PC2 and POz, and alpha-2 at Pz and POz sites were significantly decreased during muscle pain when compared with aversive noise stimulation. These results indicate that specific EEG patterns are associated with human pain processing.