Computational protocol: The influence of trait anxiety and illusory kinesthesia on painthreshold

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Protocol publication

[…] The participants were students recruited from a Kio university campus. Participants with severe chronic uncontrolled pain or central/peripheral nervous system disorders were excluded. All participants were informed at the start of the study that they could discontinue participation at any time. A total of 35 healthy right-handed students (14 males, 21 females; mean age, 22.5 ± 1.5 years) participated in this study. We explained the details of the experimental procedure, but, to limit bias in the results, we did not explain the purpose of the experiment. Before participating, the participants provided written informed consent. The study protocol was approved by the ethics committee of our university (approval number: H25-25) and the study was conducted in accordance with the ethical standards of the 1964 Declaration of Helsinki (and subsequent revisions). All included participants provided informed consent.The STAI-trait was used to examine trait anxiety). The widely used STAI-trait is a 20-item self-report questionnaire that measures predisposition to trait anxiety. We asked participants to give self-ratings regarding how they generally felt on four-item scales from 1 (almost never) to 4 (almost always). The sum the scores for the 20 items gave the total score. The STAI-trait was administered only one time before the task because trait anxiety is not known to change in the short term.Pain thresholds were measured by applying stimuli to the back of the right forearm (5 cm from the extensor digitorum muscle tendons at the radiocarpal joint) using a thermal stimulator (UDH-105, UNIQUE MEDICAL, Tokyo, Japan). The thermal probe was 20 mm in size and was placed directly on the measurement point. Measurement was performed in accordance with the protocol described by Yarnitsky et al). The thermal stimulus started at 32 °C with a 1 °C increase per second. The temperature at which the participant felt the stimulus as painful was recorded as the pain threshold. At the moment they felt pain, participants were instructed to press the switch on the remote control in their right hand to prevent further temperature increase. Before formal testing, thermal stimuli were introduced a few times to a non-assessed area, such as the center of the back of the hand, to allow participants to become sufficiently accustomed to the pain caused by the thermal stimuli. The maximum temperature of the administered stimuli was 50°C. The pain threshold was measured three times and recorded as the mean of the three values.In the present study, the method for illusory kinesthesia followed that outlined by Imai et al). For vibratory stimulation, a vibratory stimulation device (SL-0105 LP; Asahi Seisakusho Co., Ltd., Saitama, Japan) was set at 80 Hz according to previous research, which stated that the optimal tendon vibration frequency for eliciting illusory kinesthesia was 70–80 Hz,,). Participants were instructed to relax in a sitting position with their eyes closed during the trial, because it has been reported that illusory kinesthesia is unlikely to occur without muscle relaxation) and because visual information can disrupt the illusion of motion), respectively.For the procedure, participants put their hands together in a resting position on the table with their eyes closed. Vibratory stimulation was then administered to the extensor digitorum muscle tendons on the radiocarpal joint. The intensity of the subjective illusory kinesthesia was evaluated on the basis of responses to the following the question: “Does it feel like the vibrated hand was flexed”? A 6-point verbal rating scale (VRS) from 0 (strongly disagree) to 5 (strongly agree) was used.Based on the experience of subjective illusory kinesthesia, participants were divided into illusion and no-illusion groups. Among these, 22 were included in the illusion group and 13 were included in the no-illusion group. Those with any sense of illusory kinesthesia (VRS intensity 1–5) were placed in the illusion group, and those with no sense of illusory kinesthesia (i.e., VRS 0) were placed in the no-illusion group. The illusory kinesthesia angle was measured on a digital photograph of the side subject to vibration. This photograph was analyzed using the ImageJ software for measurement against the illusory kinesthetic angle. Digital photograph images are those of the position of wrist during vibratory stimulation and flexion. Flexion (illusory angle) was measured with the forearm in the neutral position with the radius as the standard axis and the second metacarpal bone as the axis of movement.First, before the experimental task, we measured the pain threshold and trait anxiety in all participants at rest, in a sitting position. Second, vibratory tendon stimulation was performed as the experimental task. The task protocol involved three cycles of resting for 10 s followed by vibratory stimulation for 30 s, as described. After the task, we measured the pain threshold, the illusory kinesthetic angle, and the intensity of illusory kinesthesia. The intensity of illusory kinesthesia was evaluated using a 6-point VRS, and the illusory kinesthetic angle was reproduced on the side subject to vibration.Participant age and STAI-trait score were compared between the illusion and no-illusion groups by t-tests, whereas gender comparisons were evaluated by χ2 tests. The pain threshold was analyzed using two-way analysis of variance (ANOVA) for two binary factors, ‘‘group’’ (illusion vs no-illusion) and period (before vs. after the stimulation). The Bonferroni method was used for post hoc comparisons. Pearson product-moment correlation coefficient was used to investigate the relationship between the amount of change in pain threshold (for the illusion and no-illusion groups) and STAI-trait score. The significance level was set at p<0.05, and we used SPSS statistics, Version 17.0 (SPSS Institute Inc., Chicago, IL, USA) for statistical analysis. […]

Pipeline specifications

Software tools ImageJ, SPSS
Applications Miscellaneous, Microscopic phenotype analysis
Organisms Homo sapiens