Differences in perception and brain activation following stimulation by large versus small area cutaneous surface...

Application of electrical stimulation through conventional surface electrodes activates both non-nociceptive and nociceptive fibres. To encompass this problem, electrical stimulation through small area pin electrode was introduced where subjective description of stimulation quality indicated preferential activation of nociceptors. The present study aimed to show that brain areas involved in nociceptive processing are activated by stimulation through cutaneous pin electrode (CPE) to a larger extent than conventional surface electrodes.

Evoked potentials (EPs) were induced by electrical stimulation through conventional surface and CPE electrodes. The EPs were recorded from 62 scalp electrodes in 12 healthy volunteers where stimulation intensity was 10 times the sensory threshold. Dipolar models of brain sources were built by using the brain electrical source analysis.

The solution for the conventional large area surface electrode was a four-dipole model including contralateral primary somatosensory cortex, bilateral secondary somatosensory cortex (SII) and mid-cingulate sources. The solution for CPE was a five-dipole model and very similar to that previously described to explain the topography of laser EPs. The solution included bilateral SII, bilateral insula and mid-cingulate sources. Since laser stimuli mainly activate nociceptive fibres, the strong similarity suggests that mainly nociceptive inputs are involved in generation of CPE-evoked responses.

The current study gives evidence that CPE activates the nociceptive brain areas to a greater extent than conventional surface electrode. Therefore, CPE should preferentially be utilized in future studies where electrical stimuli are used to study nociception.