title: Beep tones attenuate pain following Pavlovian conditioning of an endogenous pain control mechanism.
abstract: Heterotopic noxious counter-stimulation (HNCS) is commonly used to study endogenous pain control systems. The resulting pain inhibition is primarily based on spinal cord-brainstem loops. Recently, functional imaging studies have shown that limbic structures like the anterior cingulate cortex and amygdala are also implicated. Since these structures are involved in learning processes, it is possible that the HNCS-induced pain inhibition may depend on specific cues from the environment that have been associated with pain reduction through associative learning. We investigated the influence of Pavlovian conditioning on HNCS-induced pain inhibition in 32 healthy subjects by using a differential conditioning paradigm in which two different acoustic stimuli were either repeatedly paired or unpaired with HNCS. Series of noxious electrical pulse trains delivered to the non-dominant foot served as test stimuli. Diffuse noxious inhibitory control (DNIC)-like effects were induced by concurrent application of tonic HNCS (immersion of the contralateral hand in ice water). Subjective pain intensity and pain unpleasantness ratings and electromyographic recordings of the facial corrugator muscle and the nocifensive RIII flexion reflex were used to measure changes in pain sensitivity. HNCS induced significant pain and reflex inhibitions. In the post-conditioning phase, only the paired auditory cue was able to significantly reduce pain perceptions and corrugator muscle activity. No conditioned effect could be observed in RIII reflex responses. Our results indicate that the functional state of endogenous pain control systems may depend on associative learning processes that, like in the present study, may lead to an attenuation of pain perception. Similar albeit opposite conditioning of pain control mechanisms may significantly be involved in the exacerbation and chronification of pain states.
authors.affiliation: Laboratory of Psychobiology and Neurophysiology, Integrative Research Unit on Social and Individual Development, University of Luxembourg, Luxembourg, Grand-Duchy of Luxembourg.
authors.forename: Raymonde
authors.initials: R
authors.lastname: Scheuren
authors.affiliation: Laboratory of Psychobiology and Neurophysiology, Integrative Research Unit on Social and Individual Development, University of Luxembourg, Luxembourg, Grand-Duchy of Luxembourg.
authors.forename: Fernand
authors.initials: F
authors.lastname: Anton
authors.affiliation: P.A.I.N. Group, Boston Children's Hospital, Waltham, Massachusetts, United States of America ; Department of Anesthesia, Harvard Medical School, Boston, Massachusetts, United States of America.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Erpelding
authors.affiliation: Institute of Health Promotion, St Theresa Clinic, Luxembourg, Grand-Duchy of Luxembourg.
authors.forename: Gilles
authors.initials: G
authors.lastname: Michaux
mesh_terms: D000161:Acoustic Stimulation; D000293:Adolescent; D000328:Adult; D000679:Amygdala / Q000502:physiology; D003214:Conditioning, Classical / Q000502:physiology*; D003463:Cues; D004558:Electric Stimulation; D005152:Facial Muscles / Q000502:physiology; D005260:Female; D006179:Gyrus Cinguli / Q000502:physiology; D006801:Humans; D008297:Male; D009433:Neural Inhibition / Q000502:physiology; D059225:Nociception; D010146:Pain / Q000503:physiopathology / Q000517:prevention & control* / Q000523:psychology; D010147:Pain Measurement; D012018:Reflex / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology