Phase-locked and non phase-locked EEG responses elicited by intranasal nociceptive chemosensory stimulation to explore trigeminal function in humans

Huart, Caroline [UCL] Rombaux, Philippe [UCL] Mouraux, André [UCL]

Background and aims: Brief and selective chemical stimulation of olfactory and trigeminal receptors of the nasal mucosa can be used to elicit chemosensory event-related potentials (ERPs) and, thereby, study chemosensation. In particular, intranasal stimulation with gaseous C02, which produces an odorless stinging and burning sensation, can be used to selectively activate chemosensitive nociceptors of the second trigeminal branch. The aim of this study was to characterize the phase-locked ERPs, as well as the non phase-locked event-related synchronization and desynchronization (ERS and ERD) triggered by nociceptive trigeminal chemosensory stimulation in healthy subjects, and to compare the obtained responses to those elicited by thermal laser stimulation of heat-sensitive skin nociceptors. Methods: The EEG was recorded in ten healthy volunteers, using 64 scalp electrodes. A constant airflow olfactometer was used to deliver 60 pulses of CO2 (concentration: 50%v/v; rise-time: 20 ms; ISI: 30 s). Time-domain averaging was used to characterize ERPs. A time-frequency decomposition based on the Morlet wavelet transform was used to characterize ERS and ERD. Results: In all participants, nociceptive chemosensory stimulation elicited clear ERPs consisting of a negative wave (391±55 ms) followed by a positive wave (554±57 ms), as well as ERS (490 ±74 ms, 3.48 ±0.94 Hz) and ERD (813 ±140 ms, 8.94 ±1.21 Hz). The obtained responses were very similar to the EEG responses to thermal stimulation of skin nociceptors. Conclusion: Selective stimulation of chemosensitive nociceptive free nerve endings of the nasal mucosa using gaseous CO2 can be used to study nociceptive trigeminal function in humans