Ph.D. Defence by Mikkel Thøgersen

Program

Dowload Program

Abstract

The phantom limb pain condition has been puzzling researchers for decades. De-spite that it is a well-studied and a common ailment for amputees, its origin and treatment is still unclear. In the previous two decades the dominant hypothesis in the field has been that maladaptive reorganizations in the cortex happen as a result of deafferentation and ultimately results in phantom pain. While it remains a ques-tion whether these reorganizations are causal, many new strategies to treat phantom limb pain are based on this hypothesis. This line of treatments was pioneered by the mirror box illusion wherein amputees could see a recreated visualization of their lost limb. The goal of using this illusion has been to recreate sensory feedback to stimulate the dormant cortical representation of the lost limb and thereby reverse the maladaptive cortical changes. In a recent study, the efficacy of the mirror illu-sion was investigated. The authors found that pain relief had a significant correla-tion to how much the patients could relate to the visualization of their lost limb. Furthermore, the study showed that phantom limb patients with a telescoped phan-tom, i.e. the feeling that the phantom has retracted towards the stump, did not obtain a pain relief from the treatment. This research points to a possible connection be-tween body perception, cortical reorganizations and pain.
Inline with these results, this PhD thesis concerns a series of three studies investi-gating how body perception, cortical plastic changes and pain processing are af-fected by a manipulation of the visual feedback in both healthy participants and phantom limb patients. Through this work, a special platform based on augmented reality was developed to study the above factors.
Following an introduction into the area of research, the initial chapter explores the link between vision, pain and body representations. To investigate these topics, a novel augmented reality platform was created and used to manipulate own-limb visual feedback. A study was conducted on healthy participants whom experienced a complete loss of visual feedback from the left upper limb. The influence of loosing vision of the limb was assessed using both questionnaires related to the sense of ownership and agency over their arm, but also their response to nociceptive thermal stimuli. The final study focused on phantom limb pain patients and the recreation of visual feedback of their missing limb, based on the perception of their phantoms. A two-week training paradigm was used to induce up to 52% pain relief and signif-icant changes in cortical activity, indicating a possible reorganization in the soma-tosensory cortices. Perception and integration of the visualized phantom seems to be an important factor in gaining pain relief.