By: Dr. Reina Isayama: MSc candidate at University of Toronto, Toronto Western Hospital/Krembil Research Institute (March 2016)
In psychology research, illusions are often used to examine how sensory information is processed in the human brain. More than 15 years ago, researchers reported a very intriguing illusory experience in which participants were convinced that an artificial rubber hand belongs to their body. In the experiment, healthy individuals viewed a rubber hand being touched while their unseen own hand was synchronously being touched. The participants experienced an illusory feeling of ownership of the rubber hand and perceived the location of their unseen own hand shifted towards the rubber hand owing to integration of sensory inputs from vision, touch, and position sense in the brain.
The rubber hand illusion has been tested in several neurological and psychiatric disorders. In individuals with focal hand dystonia, the rubber hand illusion was reported to be reduced. However, the reasons for the diminished rubber hand illusion in focal hand dystonia remains unclear and how the rubber hand illusion changes the brain physiology is still not fully understood. My study, generously supported by DMRF Canada and CIHR, focused on the modulation of the interaction between sensory and motor cortices (the main brain areas responsible for sensory and motor functions) during the rubber hand illusion because the reduced rubber hand illusion in focal hand dystonia may be related to the motor symptoms of dystonia.
I tested more than 30 healthy individuals using transcranial magnetic stimulation (TMS), which is a non-invasive way to stimulate a focal part of the brain through the scalp, and recorded responses from hand muscles before and immediately after the rubber hand illusion. I found that the functional connections between the sensory and motor cortices are reduced after the rubber hand illusion. I propose that this flexibility of sensory-motor interactions may be compromised in focal hand dystonia, leading to reduction of the illusion.
This finding was presented at several international conferences including the International Congress of Clinical Neurophysiology, the Society for Neuroscience annual meeting and the International Parkinson and Movement Disorder Congress. We are now examining the interaction between sensory and motor cortices in people with focal hand dystonia using TMS during writing preparation. We are very excited about this project because we believe that our findings will further our understanding of the pathophysiology of dystonia and help to design neuromodulation therapies using TMS and other types of the brain stimulation for people suffering focal hand dystonia. I would like to thank CIHR and DMRF again for giving me this opportunity to perform these projects. I will continue my research in movement disorders such as dystonia and am looking forward to contributing further to the field