Giselle ChristoffersenSupervisor: Laura Petrini

In association with the Department of Psychology, KANUK and Center for Sensory-Motor Interaction at Aalborg University

AimsThe aim of this studyis to Investigate howplacebo analgesia

effectsthe subjective

perceptionof pain and

psychologicalaspects such as the

roleof the experimenter

andthe participant’sexpectancy. The brainactivity was recorded

by measuring ERPs.

ResultsResults

IntroductionThe placebo effect has been a scientific field of interest since the 1950’s and has since then been found to have a multitude of effects, specifically in relieving pain: placebo analgesia (PA). However there’s an inconsistency in the literature regarding who experiences PA and the intensity of the effect.

MethodSubjects were 25 healthy students age range 21-32 (mean 25,5 years). All participants were assigned to 4 conditions (B, M, AN, AN NP) with 2 pain intensities (VRS 4, VRS 7) each (see Fig.1). The pain was induced by 60 electrical stimulations applied to the surface of the left index finger with a 2 second interval. A NoxiSTIM stimulator was used. The placebo was an odourless, thick, white moisturizing lotion, which was applied on the index finger and was presented in condition M as a regular moisturizing lotion and in condition AN as an effective analgesic lotion. The EEG was recorded from 128 scalp sites using the 10-5 system montage by ANT-EEProbe. Electrodes impedences were kept below 5KΩ. The EEG was digitezed at 512 Hz with amplifier bandpass of 0.3-30Hz. Repeated measures of ANOVAs (condition x pain intensity) were conducted. The subjective pain perception was measured using a 10 point Visual Rating Scale (VRS)

Discussion/ConclusionIn the present study the subjective perception of pain (evaluated using VRS) was compared in 4 different conditions within subjects. VRS results were then compared with ERP responses. The results only showed a significant difference in conditions AN4 and ANNP4, indicating that the placebo lotion only has an effect on low intensities of pain. Furthermore these results show that the presence of the experimenter is needed in order for the placebo to be effective. The EEG data show the difference in ERPs in different conditions, supporting the reduced subjective pain ratings in condition AN4.

Hypotheses1. In the presence of the

experimenter, the participants report a lower pain intensity than when the experimenter is not present.

2. The amplitude of ERPs illustrate that the neurophysiological response to pain in the placebo condition (AN, AN NP) does not differ greatly from baseline (B).

The neurophysiological response to pain was more intense when the experimenter was not present.

Baseline – VRS 4

”Analgesic lotion” with no presence of experimenter - VRS 4

Data from grand average of 19 participants.

The first participant

”Analgesic lotion” – VRS 4

Fig.3

References[1] Hrobjartsson, A., Gotzsche, PC. (2004) Is the placebo powerless? Update of a systematic review with 52 new randomized trials comparing placebo with no treatment. Journal of Internal Medicine, 256.[2] Kirsch, I. (1985) Response expectancy as a determinant of experience of behavior. Am Psychol 40.[3] Volkow, ND., Wang, GJ., Ma, Y., et al. (2003) Expectaion enhances the regional brain metabolic and the reinforcing effects of stimulants in cocaine abusers. Neuroscience 23.

AcknowledgementsLaura Petrini, Ph.D., Department of Health Science and Technology, SMI, Aalborg University.Jørn Ry Hansen, Department of Psychology, Aalborg UniversityLi Wang, M.Sc.Eng., Ph.D StudentThe KANUK team

The data on the subjective perception of pain showed only a significant placebo effect between AN4 and ANNP4 (F(21,3) = 67,459, p = 0.003) , but no significant effect between the other conditions.EEG data showed that the neurophysiological response to pain is more intense when the experimenter is not present (Fig.2).Furthermore, prominent amplitudes were found among 4 components in the EEG data. Conditions B4, AN4 and AN NP4 are illustrated (Fig.3).

Fig.1

Conditions within subjects

Component 1 Component 2 Component 3 Component 4

Component 1 Component 2 Component 3 Component 4

Component 1 Component 2 Component 3 Component 4