Topographic analysis of painful laser and sural nerve electrical evoked potentials.

A quantitative scalp topographic pattern analysis was used to compare evoked potentials elicited by painful laser (LEP) and electrical stimulation of the sural nerve (snSEP) in 22 healthy adults. The snSEP and LEP were separated into stable periods (consecutive time points having the same topographic pattern). The topographic pattern is dependent upon the number, location, orientation and relative magnitudes of the brain areas active at that time (source configuration). Demonstrating that 2 topographies have the same topographic pattern, therefore, provides evidence that they are generated by the same source configuration. The snSEP SP2/3 and SP3 stable periods have similar topographic features as the stable periods encompassing the LEP N1 and N2 peaks. However, the quantitative scalp topographic analysis demonstrated that the snSEP SP2/3 and SP3 have a much larger fronto-central negativity. Our earlier work suggests this difference might be due to the sural nerve electrical stimulus evoking a more robust pain-evoked response from the anterior cingulate cortex than the laser. The snSEP SP6 topographic pattern was essentially the same as the LEP P2 peak. This finding plus the results of our earlier work demonstrate that SP6 is the snSEP analogue of the LEP P2 peak. These findings have important implications for the choice of evoking stimulus in investigations of pain processing in humans. For example, the sural nerve electrical stimulus will be preferred over the laser in studies of the anterior cingulate's role in cognitive processes related to pain, such as orienting attention, and/or in studies involving cognitive tasks that require the presentation of a large number of painful stimuli. The LEP N1 and N2 peaks, on the other hand, will be preferred in studies of the parietal operculum's role in pain sensation.