Psychopharmacology (2011) 215:537–548 the first author and the experimenter during the experimental sessions. Laser stimulation and calibration An Nd:YAP laser (Stimul 1340, El.En. Group, Firenze, Italy) was used for laser-induced heat pain. The laser had a wavelength of 1,340 nm and selectively activated Aδ- and C-fibers. Spot diameter was set to 6 mm and duration to 4 ms. An upper limit of 4.5 J was set in order to avoid damage to the skin. Subjects and experimenters wore protective goggles. Laser stimulation was controlled by TTL-pulses defined in E-prime software (Psychology Software Tools, Inc., Pittsburgh, USA) run on a Dell computer. The intensity of the pain stimulus was calibrated for each subject in order to make sure subjects experienced similar amount of pain. Subjects were seated in a comfortable chair and instructed in how to report pain. Laser stimuli were presented to the medial volar forearm, and the laser head was moved randomly between each stimulus. Stimuli were presented in an ascending series starting at 0.5 J, with an increase rate of 0.25 J, until the subject reported 4 (pain threshold) or higher on the NRS. The next series was descending from 1 J above threshold, with a decrease rate of 0.25 J, until the subject reported 4 or lower on the NRS. Two ascending and two descending series were performed. Pain threshold was determined as the average stimulus intensity where the subject reported the lowest level of pain. The stimulus intensity to be applied in the test phase in the four experimental conditions was 1.5 times pain threshold, or maximum of 4.5 J. Procedure The experiment was performed in a laboratory at the Department of Psychology between 9 a.m. and 6 p.m. The lab contained a chamber (2.8×2.8 m) shielded for electro- magnetic disturbance and sound in which the pain tests and EEG recordings were done. Apparatus for control of painful stimulation and for recording of EEG were placed outside the chamber. On the day of testing, subjects met between 9 a.m. and 4:30 p.m. Testing lasted about 90 min. On the first day, the experimenter ascertained that the subjects met the inclusion criteria and had read and signed the informed consent. A cover story was presented in the informed consent form: Subjects were informed that they participated in an experiment that investigated the effect of expectations and learning on the effectiveness of an over-the-counter painkiller. The subjects were told that it was tested to what degree the effectiveness of an over the counter painkiller varies according to ones response expectancies. They were further informed that this required measurement of their 539 response to a painful stimulus before and after receiving a painkiller in addition to measurement of their expectations. Finally, in order to explain why 4 days of testing were needed, the participants were told that two tests with and two tests without administration of a painkiller were necessary in order to get reliable data. These four test days were the four conditions of the balanced placebo design: a control condition (no drug/got no drug information), a placebo condition (no drug/got drug information), a caffeine condition (drug/got no drug information) and an active placebo condition (drug/got drug information). All subjects participated in all four conditions. The order of presentation of the conditions was different for all subjects. After informing subjects about the purpose of the study, the participants were weighed and the experimenter reported the weight to the first author via telephone. Immediately thereafter, the intensity of the laser stimulus was calibrated for each subject according to the procedure described above. After calibration, the electrode cap for recording of electroencephalography was placed on the subjects. Sub- jects were then led into the shielded chamber, placed in a comfortable chair and told that the test phase would start. The test phase in each experimental condition consisted of a pretest, a pause and a posttest. The pretest lasted about 5 min and started with measurement of stress and arousal followed by 20 laser stimuli delivered on the T1 dermatome of the non- dominant medial volar forearm. Immediately thereafter 1.5 dl of chilled grapefruit juice with 0 or 4 mg/kg caffeine was served with information that it contained an over-the-counter painkiller that would reduce the pain (“got drug” information) or that it contained no drug (“got no drug” information). Subjects were told to wait for 30 min so that the drug could be absorbed or to wait a similar amount of time when “got no drug” information was provided. The posttest was identical to the pretest. Immediately after the posttest, subjects were asked to remember and report accurately what their expectations were at the time the posttest started. In the pre- and posttest, each laser stimulus was signalled by a 1 kHz tone with 1,000 ms duration that had onset 3 s before the laser stimulus. The purpose of the auditory cue was to produce an interval in which stimulus preceding negativity (SPN) could be measured, which previously has been observed in the anticipation of a painful stimulus (Brown et al. 2008; Böcker et al. 2001). The SPN data are not reported here. The inter-trial interval was varied between 5 and 14.5 s in randomised order. Subjects reported pain intensity 2–3 s after each stimulus. The laser head was held by the experimenter who sat beside the participant in the shielded chamber and moved it between each stimulus in order to avoid sensitization, habituation or skin damage. The participants met four times in the laboratory with a minimum of 24 h between each test. With the exception of