ERP CORRELATES OF PLACEBO AND "ANTI-PLACEBO" EFFECTS.

In the study we observed the effects of placebo and "anti-placebo" messages on the neural activities registered through the event related potentials (ERP). Instead of commonly used term nocebo, we used the term "anti-placebo", given that the message we delivered was not supposed to induce the negative effects, but just to diminish the effect of placebo. Thermal stimulus of 45 degrees of Celsius was applied on the skin of 29 students in a four different experimental situations: without analgesia, after receiving dermal analgesic EMLA Cream, after receiving neutral skin cream presented as an analgesic (placebo situation), and after receiving again EMLA Cream, but presented as the herbal analgesic not officially accepted as a medicament ("anti-placebo" situation). Immediately after stimulation, participants were asked to estimate the level of "unpleasantness" of the stimuli on the subjective scale ranging from 1-10, and to start a cognitive experiment, during which the ERP responses were measured. Results showed three main ERP effects. In the early effect, we noticed that all three experimental situations with analgesia (that is, two conditions with the pharmaco-analgesia + the condition with the placebo analgesia) showed a different ERP effects in comparison to the condition with no analgesia. We interpreted these results as early expectancies that any analgesic (including placebo) should produce some effect in comparison to no-analgesic condition. In the medium effect, we observed significantly longer durations of the ERP effects in the situation of the "anti-placebo" and no-analgesia, whereas in the analgesia and placebo condition these effects were much shorter. This result led us to the conclusion, that on the neural level, our suggestion of "bad medicament" (similar to situation of no-medicament) caused a specific mental activity registered on ERP. This effect is the one which calls into a question doctors' ecommendations (which contain negative connotation) of medicaments, as they could potentially and unconsciously diminish a valuable impact hat the placebo could have during a treatment. Finally, in the late effect, we also observed significant differences across the four experimental conditions, but these differences were directly correspondent with the order of presentation of experimental situations, and we interpret them as an artefact of the experimental design. [ABSTRACT FROM AUTHOR]

U ovom istraživanju bavili smo se neuralnim korelatima efekata placebo i „anti-placebo" poruka putem merenja moždanih talasa (ERP). Umjesto uobic^ajenog termina nocebo, koristili smo termin „anti-placebo", budući da poruke koje smo zadavali ispitanicima nisu trebale da proizvedu negativne efekte, već da umanje ili ponište efekat placeba. Primenili smo termalnu draž intenziteta 45 stepeni Celzijusa na kožu podlaktice. Ukupno je 29 studenata uzelo učešća u četiri eksperimentalne situacije: bez analgezije, nakon primene analgezije (korišćenjem EMLA kreme), nakon primene neutralne kreme koja je prezentovana kao analgetik (placebo situacija) i nakon primene EMLA kreme koja je prezentovana kao herbalna krema koja nije zvanično prihvaćena kao medikament („anti-placebo“ situacija). Neposredno nakon stimulacije, od ispitanika je zatraženo da procene nivo neprijatnosti na subjektivnoj skali osetljivosti 1-10, a nakon toga im je zadat kognitivni eksperiment, tokom koga su mereni ERP odgovori. Rezultati su pokazali tri glavna ERP efekta. U ranom efektu, sve tri eksperimentalne situacije koje su podrazumevale primenu anelgezije (tj. dve situacije sa farmako-anelgezijom + situacija sa placebo-anegle-zijom) pokazale su različite profile ERP efekata u odnosu na situaciju u kojoj nije primenjena anelgezija. Ovaj rezultat smo interpretirali kao rano očekivanje da bilo koja vrsta anelgezije (uključujući placebo) treba da proizvede nekakav efekat, za razliku od situacije u kojoj nije bilo primene analgezije. Središnji ERP efekat je demonstrirao duže trajanje ERP efekata u situaciji sa „anti-placebom“ i u situaciji bez analgezije, dok su u situaciji sa primenom analgezije i u placebo situaciji ovi efekti bili mnogo kraći. Ovaj nas je rezultat naveo na zaključak da, na neuralnom planu, sugerisanje da je neki lek „anti-placebo“ proizvodi sličan profil ERP ili sličnu mentalnu aktivnost kao u situaciji bez leka. Ovaj rezultat poziva na preispitivanje preporuka lekara da neki lekovi nisu baš dobri, jer ovakve sugestije mogu potencijalno i nesvesno da umanje inače pozitivan efekat koji placebo ima tokom tretmana. Na kraju, u poznom efektu smo takođe uočili razlike između četiri eksperimentalne situacije, ali su ove razlike u vezi sa redosledom izlaganja eksperimentalnih situacija, te smo ih interpretirali kao artefakt eksperimentalnog dizajna. [ABSTRACT FROM AUTHOR]