Cerebral event-related responses induced by CO2 laser stimulation in subjects suffering from cervico-brachial...

The present study was undertaken to examine possible changes in subjective appraisal and central nervous system processing, indexed by pain-related cerebral evoked potentials (N290, P400), of incoming noxious information in 20 pain-free control volunteers and 18 subjects suffering from right-side cervico-brachial pain (CBS). Detection threshold and cerebral evoked potentials were recorded in response to noxious CO2 laser stimulation of the right and left hands. The results indicate that when compared to controls, CBS subjects exhibit an elevation in detection threshold intensity and a reduction in the amplitude of the P400 peak following laser stimulation of the pain affected side. There were also differences in the choice of qualitative descriptor for laser stimuli although not in the subjective rating of stimulus intensity. These changes were not apparent for responses on the unaffected limb. The severity of clinical pain was found to be related to the magnitude of reduction in P400 amplitude only on the pain affected side. Conversely, feelings of anxiety were associated with higher amplitude responses on both the right and left sides, suggesting a more generalized relationship between these factors. We interpret these findings to indicate an alteration in central nervous system processing and subjective appraisal of acute experimental pain in subjects with chronic CBS. Moreover, these alterations appear to be restricted to pain affected pathways and are more related to the severity of clinical pain than to general mood state.