RESUMO
BACKGROUND: Commonly used models for eliciting muscle pain involve the injection of algesic substances or the induction of delayed onset muscle soreness. The former require invasive procedures, and the time frame for pain induction and subsidence in the latter can be inconvenient. This study presents a detailed spatiotemporal characterization of a new experimental model of muscle pain based on short-wave diathermy (SWD), developed to overcome the limitations of existing models. METHODS: The shoulder was selected as target site and the effects of the model were tested in two sessions to assess its reliability. Pain intensity profiles were recorded during the application of SWD, and changes in pressure pain threshold (PPT) in the infraspinatus muscle, together with pain intensity, duration, and quality were assessed 30 min after induction. RESULTS: SWD-induced pain intensity scores averaged 4 points on a visual analogue scale, whereas PPT showed a consistent decrease of about 25% relative to baseline values. Pain was localized in the shoulder area, and was described as continuous, dull, well-delimited, heavy, and bearable. Pain lasted for an average of 145 min without requiring reinduction and was reliably elicited in both experimental sessions. CONCLUSION: SWD can be used to elicit experimental muscle pain in a non-invasive, long-lasting, and reliable way and allows for repeated within- and between-session testing in the shoulder. SIGNIFICANCE STATEMENT: SWD produces deep heating in muscles by converting electromagnetic energy to thermal energy. It was previously shown that it can be used to elicit experimental pain in the forearm muscles, and the present study demonstrates that this can be reliably generalized to other body sites, such as the shoulder. Furthermore, SWD application is non-invasive and presents a convenient time frame for pain induction and subsidence, thus overcoming limitations associated with traditional muscle pain models.
RESUMO
Several models have been developed to analyse cortical activity in response to salient events constituted by multiple sensory modalities. In particular, additive models compare event-related potentials (ERPs) in response to stimuli from two or more concomitant sensory modalities with the ERPs evoked by unimodal stimuli, in order to study sensory interactions. In this approach, components that are not specific to a sensory modality are commonly disregarded, although they likely carry information about stimulus expectation and evaluation, attentional orientation and other cognitive processes. In this study, we present an analytical method to assess the contribution of modality-specific and nonspecific components to the ERP. We developed an experimental setup that recorded ERPs in response to four stimulus types (visual, auditory, and two somatosensory modalities to test for stimulus specificity) in three different conditions (unimodal, bimodal and trimodal stimulation) and recorded the saliency of these stimuli relative to the sensory background. Stimuli were delivered in pairs, in order to study the effects of habituation. To this end, spatiotemporal features (peak amplitudes and latencies at different scalp locations) were analysed using linear mixed models. Results showed that saliency relative to the sensory background increased with the number of concomitant stimuli. We also observed that the spatiotemporal features of modality-specific components derived from this method likely reflect the amount and type of sensory input. Furthermore, the nonspecific component reflected habituation occurring for the second stimulus in the pair. In conclusion, this method provides an alternative to study neural mechanisms of responses to multisensory stimulation.