Periodic Reporting for period 1 - NeuroCon (Understanding the mechanisms of pain modulation through expectations (conscious and unconscious) in placebo analgesia induced in the context of fear conditioning - MEG and EEG study) Reporting period: 2020-09-01 to 2022-08-31 Summary of the context and overall objectives of the project Modern pharmacology provides us with several effective analgesia methods (e.g. pills, injections, creams). Despite working well for acute pain, they are ineffective for chronic pain, a major problem affecting approx. 20% of the EU population. Chronic pain can persist for months or even years and is associated with an over-sensitive and over-responsive nervous system. In contrast to acute pain, it is not caused by physical damage to the body and is believed to result from a complex interplay of biological, psychological and social factors, where conditioned pain-related fear is partially responsible for the symptom's chronicity maintenance and perpetuation. For this reason, even strong opioids are usually helpless but often overprescribed. Their abuse is a serious health problem which can even lead to death through overdose.As a result, it is crucial to investigate other analgesia methods not based on active substances. Their effectiveness depends on many factors, e.g. earlier positive/negative experiences or our attitude and expectations related to their effectiveness. Such relationships are acquired via a learning mechanism called classical conditioning (CC). In CC a previously neutral stimulus (the conditioned stimulus, CS) is paired with a biologically potent stimulus (the unconditioned stimulus, US) and starts to elicit a conditioned reaction (CR) that is similar to the one elicited by the US. Our cognition modulates pain perception and placebo analgesia, which works through the expectation of pain decrease induced via CC, is the best example of it. Concluding, laboratory studies where placebo manipulation is introduced during fear conditioning may help to recognise the specific role of expectations that modulate pain perception. Moreover, investigating fear conditioning processes can be important to explain and find markers that may help in the early recognition of potential pain problems. Specifically, examining how the sensory response system adapts to relevant or irrelevant information and recognising the abnormalities in this process provides a promising method of prediction of further disabilities. Such investigation has great potential in clinical practice since it can help develop adequate pain therapy and pain management strategy. Consequently, the main objectives of this project were to understand the mechanisms of information prioritization, how neutral stimuli gain their relevance in the process of learning (fear conditioning) and to investigate if placebo manipulation (consciously or unconsciously formed expectations) influences different aspects of experience (e.g. during anticipation of pain/mid-pain/tactile/no-stimuli delivery, administration of stimulus and post-stimulus pain ratings). Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far We employed the MEG neuroimaging technique in the context of the fear conditioning paradigm to determine how sensory cortices are modified to better detect and distinguish relevant information of different levels of importance. Namely, we used two conditioning stimuli (Gabor patches) predicting pain (CS+P) and mid-pain stimulation (CS+M), and two safe CSs where no stimulation (CS-0) or painless tactile stimuli (CS-T) were delivered. Next, we investigated if the expectation of pain reduction learned through CC in the acquisition phase would be sustained in the testing phase where after CS+ identical stimulation was applied to the participants in placebo groups. We measured steady-state visual evoked field (ssVEF) amplitude modulation that follows CSs presentation. Precisely, ssVEFs were elicited by a repetitive visual stimulus (4 Gabor patches) that is periodically modulated in intensity at a fixed rate of 15 Hz and evokes a sustained reentrant neuronal oscillatory activity in the visual cortex that has the same fundamental frequency as the driving stimulus. Besides the excitatory properties of the CS+M and CS+P, inhibitory properties of the non-reinforced (safe) cues (CS-0 and CS-T) were investigated. Next, considering the importance of expectation in conditioning (conscious and/or unconscious expectations elicited in CCV and CCH groups), ssVEFs have great potential in elucidating the neural mechanisms of expectation forming during fear learning processes and its role in placebo effects. In order to indicate if placebo manipulation works, behavioural measurements (individual stimuli ratings) were collected after each pain stimulation (US) delivery.Our preliminary analysis performed on the ssVEF data collected in the first registration period indicates increased cortical source space effect (ssVEFs: CS+P–CS-0 and CS+M–CS-0 differences) in acquisition compared to both habituation and extinction phases for CCH. In the case of CCO group, analogous effects were observed, however only for the CS+M–CS-0 difference. Between-group comparisons indicate higher ssVEFs general cortical source space effect for the CS+M–CS-0 effect for the CCH compared to CCO group. There was no difference between the acquisition and testing phases for both groups. The analysis of all collected behavioural data for both CCH and CCV group indicate a lack of placebo analgesia induction. However, we observe that the type of conditioning influenced the ratings of the CS+, making them less pronounced in CCV compared to CCH group. Unfortunately, for behavioural measurements for both CCH and CCV groups, no placebo analgesia was observed during the TF.The project results were presented at the Society for Neuroscience (SfN) conference in San Diego, shared with the scientific community during three invited talks, disseminated via the project website and shared with the interdisciplinary C3N group meetings. The results of the MEG analysis are under preparation for publication and the manuscript describing the novel calibration protocol is under revision. Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far) Our results replicate previous findings of increased ssVEFs response in the conditioning phase, where the CS gains its relevance - we observed an increase in ssVEF for the relevant conditioned stimuli (CS+). We also indicated that the type of conditioning (open vs hidden) may influence the magnitude of the effect. Currently, analysis of ssVEF using the GLMflex software is performed where repeated measures ANOVA with within-subject factors of the experimental phase and condition and between-subject factor groups are investigated. Behavioural data analysis indicates that in the context of the fear conditioning paradigm placebo analgesia was not induced.Aside from investigating the project's main aim, this research has accomplished an additional valuable finding. The researcher collected all the data during the calibration procedure where the stimuli strength of electric stimulation is adjusted to the individual pain perception for each of the participants. The researcher used both the classical staircase method, where the stimuli strength is increased and decreased several times to determine the sensation and pain threshold via self-reports, and a linear regression model which assumed that the data are linear. During data post-processing, it was proved that the calibration procedure can be significantly shortened, i.e. fewer stimuli can be applied (mitigating the effect of stimuli habituation) to give statistically the same result, and its reliability can be quantified. This can have a future impact on designing more accurate and reliable calibration methods crucial in laboratory and clinical pain research studies. Related documents Picture 1.png
