Motor responses are essential for protecting the body from pain, eg removing one's hand from a hot object or immobilizing an injured joint. The motor and pain systems are therefore interacting in the nervous system. In this study, we sought to understand how different components of pain (sensory and cognitive) influence the motor system.
Pain is a complex multidimensional experience that includes sensory, emotional, motor and cognitive components. For example, the intensity of the stimulation (sensory component) or knowing when the pain will be felt (temporal predictability – cognitive component) can influence the experience of pain. Our study evaluated how these two components influenced the perception of pain as well as the motor system. We used experimental pain (a laser) that activates the pain pathways in a controlled manner.
First, the results show that the perception of pain increases with the intensity of the laser. In addition, the pain is perceived to be more intense when it is predictable over time. This increased perception of pain was objectively translated into higher brain responses (measured by electroencephalography). This shows that pain depends on both sensory and cognitive factors.
Second, the results show that the higher the intensity of stimulation, the more the motor pathway that connects the motor cortex to the muscles corresponding to the painful area is inhibited, but with great variability across the participants. In contrast, the predictability of stimulation had an impact on the motor pathway only for half of the participants. This suggests that the cognitive factors of pain that influence the motor system may be related to other components (eg anxiety).
In conclusion, the influence of pain on the motor system is partly explained by sensory and cognitive factors, but questions still remain to be elucidated (eg the role of the affective component).
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