Periodic Reporting for period 3 - IllusoryPain (Illusions in the thermo-nociceptive system)
Okres sprawozdawczy: 2024-01-01 do 2025-06-30
This project seeks to answer the question: What does it mean to experience an "illusion of pain"? At first glance, the phrase may seem contradictory. Pain is a tangible experience that feels undeniably real. We generally trust our senses, assuming that when we feel pain, it is a direct consequence of some harmful interaction with our environment or damage within our body. Yet, the term "illusion of pain" refers to instances when pain is perceived, even though the triggering stimulus is harmless and would not typically cause a painful sensation in most circumstances.
In this project, one key objective is to pinpoint the specific conditions under which harmless stimuli are perceived as painful by different individuals. We hypothesise that these illusions are not just anomalies or misconceptions of our pain perception, but rather offer insights into how pain is generated within our nervous system. Therefore, we employ these illusions as tools to understand mechanisms governing pain perception in humans.
The significance of this project is evident when considering the challenges faced by individuals with chronic pain. Many suffer from chronic pain conditions that remain elusive to current diagnostic or treatment methods. Understanding why pain occurs, particularly in the absence of a clear physical cause, can offer solace to those who are told that their pain is merely imagined or feel unjustifiably dismissed by healthcare experts. Through this project, we aim to introduce a novel perspective that frames pain through its underlying mechanisms, moving beyond "nociceptive" and "illusory" labels. We posit that pain is not merely a response to harmful environmental stimuli or damage within our body, but a reflection of the complex mechanisms governing the human nervous system.
In this project, one key objective is to pinpoint the specific conditions under which harmless stimuli are perceived as painful by different individuals. We hypothesise that these illusions are not just anomalies or misconceptions of our pain perception, but rather offer insights into how pain is generated within our nervous system. Therefore, we employ these illusions as tools to understand mechanisms governing pain perception in humans.
The significance of this project is evident when considering the challenges faced by individuals with chronic pain. Many suffer from chronic pain conditions that remain elusive to current diagnostic or treatment methods. Understanding why pain occurs, particularly in the absence of a clear physical cause, can offer solace to those who are told that their pain is merely imagined or feel unjustifiably dismissed by healthcare experts. Through this project, we aim to introduce a novel perspective that frames pain through its underlying mechanisms, moving beyond "nociceptive" and "illusory" labels. We posit that pain is not merely a response to harmful environmental stimuli or damage within our body, but a reflection of the complex mechanisms governing the human nervous system.
This project focuses on two specific illusions, known as The Thermal Grill Illusion (or TGI) and Paradoxical Heat Sensation (PHS). TGI is generated by spatial alternation, while PHS is generated by temporal alternation of innocuous warming and cooling of the skin. While individual warm and cold elements are perceived as harmless in isolation, the spatial or temporal alternation of the two type of stimuli triggers hot and/or burning sensations.
WP1 and WP2
1. We introduced a novel protocol to assess PHS, affectively addressing previous methodological confounds (Schaldemose et al. Temperature 2023)
2. We showed that PHS and TGI cannot be elicited by the same temperature parameters in either spatial or temporal alteration (Shaldemose et al. Neuroscience Letters 2023)
3. We assessed the prevalence of PHS in individuals with neuropathic conditions and identified that PHS is most common in individuals with diabetic neuropathy (Vollert/Fardo et al. Pain 2023).
4. We demonstrated that PHS can be explained by contrast enhancement - a mechanistic principle that is shared across distinct sensory systems (Mitchell et al. Temporal Contrast Enhancement in Thermosensation: A Framework for Understanding Paradoxical Heat Sensation. BioRxiv Preprint)
5. We found that spinal cord mechanisms are responsible for both heat enhancement and illusory pain, two perceptually distinct facets of the TGI (Mitchell et al. Disentangling the spinal mechanisms of illusory heat and burning sensations in the Thermal Grill Illusion. BioRxiv Preprint).
WP1 and WP2
1. We introduced a novel protocol to assess PHS, affectively addressing previous methodological confounds (Schaldemose et al. Temperature 2023)
2. We showed that PHS and TGI cannot be elicited by the same temperature parameters in either spatial or temporal alteration (Shaldemose et al. Neuroscience Letters 2023)
3. We assessed the prevalence of PHS in individuals with neuropathic conditions and identified that PHS is most common in individuals with diabetic neuropathy (Vollert/Fardo et al. Pain 2023).
4. We demonstrated that PHS can be explained by contrast enhancement - a mechanistic principle that is shared across distinct sensory systems (Mitchell et al. Temporal Contrast Enhancement in Thermosensation: A Framework for Understanding Paradoxical Heat Sensation. BioRxiv Preprint)
5. We found that spinal cord mechanisms are responsible for both heat enhancement and illusory pain, two perceptually distinct facets of the TGI (Mitchell et al. Disentangling the spinal mechanisms of illusory heat and burning sensations in the Thermal Grill Illusion. BioRxiv Preprint).
Understanding pain and its underlying mechanisms remains an ongoing challenge in the medical and scientific community. This project distinguishes itself by focusing on perceptual phenomena that defy common understanding and established pain theories. We have introduced new methodologies to assess Paradoxical Heat Sensation (PHS) and the Thermal Grill Illusion (TGI), which addressed and rectified prior inconsistencies, as well provided a solid basis for new behavioural, neurophysiological and neuroimaging investigations.
We have made substantial progress in identifying the functional properties and potential mechanisms, such as contrast enhancement, that underlie heat and pain illusions. This work has also provided strong precedents to motivate further exploration of spinal cord mechanisms involved in TGI. In our ongoing work, we are using neurophysiological and neuroimaging techniques to delineate the central nervous system mechanisms associated with TGI.
We have made substantial progress in identifying the functional properties and potential mechanisms, such as contrast enhancement, that underlie heat and pain illusions. This work has also provided strong precedents to motivate further exploration of spinal cord mechanisms involved in TGI. In our ongoing work, we are using neurophysiological and neuroimaging techniques to delineate the central nervous system mechanisms associated with TGI.