Cortical activity evoked by an acute painful tissue - damaging stimulus in 1 healthy adult volunteers

27 Everyday painful experiences are usually single events accompanied by tissue damage and yet 28 most experimental studies of cutaneous nociceptive processing in the brain use repeated laser, 29 thermal or electrical stimulation that do not damage the skin. In this study the nociceptive activity in 30 the brain evoked by tissue damaging skin lance was analysed using electroencephalography (EEG) 31 in twenty healthy adult volunteers (thirteen male and seven female) aged 21-40 years. Time 32 frequency analysis of the evoked activity revealed a distinct late event related vertex potential 33 (Lance Event Related Potential, LERP) at 100-300 ms consisting of a phase-locked energy increase 34 between 1-20 Hz (delta-beta bands). A pairwise comparison between lance and sham control also 35 revealed a period of ultra-late stronger desynchronization following lance in the delta band (1-5 Hz). 36 Skin application of mustard oil before lancing, which sensitises a subpopulation of nociceptors 37 expressing the cation channel, TRPA1, did not affect the ultra-late desynchronisation but reduced 38 the phase-locked energy increase in delta and beta bands, suggesting a central interaction between 39 different modalities of nociceptive inputs. Verbal descriptor screening of individual pain experience 40 revealed that lance pain is predominantly due to Aδ fibre activation, but when individuals describe 41 lances as C fibre mediated, an ultra-late delta-band event related desynchronisation occurs in the 42 brain evoked activity. We conclude that pain evoked by acute tissue damage is associated with 43 distinct Aδand C-fibre mediated patterns of synchronization and desynchronization of EEG 44 oscillations in the brain. 45