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The role of state anxiety and state fear in placebo effects is still to be determined. We aimed to investigate the effect of fear of movement-related pain (FMRP) and contextual pain related anxiety (CPRA) on the magnitude of placebo analgesia induced by verbal suggestion. Fifty-six female participants completed a modified voluntary joystick movement paradigm (VJMP) where half participated in a predictable pain condition (PC), in which one of the joystick movements is always followed by pain and the other movement is never followed by pain, and half in an unpredictable pain condition (UC), in which pain was delivered unpredictably. By varying the level of pain predictability, FMRP and CPRA were induced in PC and UC respectively. Colour stimuli were presented at the beginning of each trail. Half of the participants were verbally informed that the green or red colour indicated less painful stimuli (experimental groups), the other half did not receive any suggestion (control groups). We measured self-reported pain intensity, expectancy of pain intensity (PC only), pain related fear and anxiety (eyeblink startle response and self-ratings) and avoidance behaviour (movement-onset latency and duration). The results indicate that the placebo effect was successfully induced in both experimental conditions. In the PC, the placebo effect was predicted by expectancy. Despite the fact that FMRP and CPRA were successfully induced, no difference was found in the magnitude of the placebo effect between PC and UC. Concluding, we did not find a divergent effect of fear and anxiety on placebo analgesia.

We investigated whether evoked potentials to omitted stimuli could be measured in rats. Such an animal model would provide a measure of aspects of information processing concerned with expectancy and time estimation. In a first experiment, omission evoked potentials (OEPs) were elicited in rats by omitting stimuli (10%) from a train of tone pips with a fixed ISI (3 s). A control session consisted of omitting stimuli (10%) from a train of tone pips with a variable ISI (2.5-3.5 s). In a second experiment, OEPs were measured in rats that received 4 mg x kg(-1) diazepam or vehicle sc. In the first experiment, half of the animals showed OEPs that consisted of a late-latency positive wave, the other rats showed a slow negative drift. No OEPs were found in the control session. Rats showing OEPs consisting of a positive wave in Experiment 1 were passed to Experiment 2. In the vehicle condition of the second experiment, all rats showed OEPs. In the diazepam condition no OEPs were found. We found that OEPs can be measured in rats. In addition, OEPs are disrupted by diazepam. We propose that OEPs provide an elegant tool to elicit selectively endogenous EP components.

In our study, we compare three popular approaches to directed coupling analysis, in particular transfer entropy and two types of Granger causality, applied to real data from genetic absence epilepsy rats. We have chosen the channels for which the coupling architecture is already well known from previous studies. Recordings from 5 WAG/Rij rats of 8 hours duration with at least 28 spontaneous seizures of length not less than 6 s in each recording were studied. To test results for significance, surrogate signals based on series permutation technique were constructed. Connectivity development in time was investigated by considering six two-second intervals before, during and after the seizure. Our outcomes showed large differences between studied approaches, while all of them exploit the same general idea. Transfer entropy demonstrated the smallest number of significant couplings throughout all three considered measures, while the linear Granger causality showed the largest number of them. This indicates that transfer entropy is the most conservative measure and the least sensitive one. Its sensitivity is affected by insufficient series length. The linear Granger causality is likely to demonstrate insufficient specificity.

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