The rubber hand illusion and deep brain stimulation in Parkinson's disease

Professor Dominic Thyagarajan

Professor Dominic Thyagarajan heads a group investigating movement disorders in the newly launched Department of Neuroscience. Here, he writes of a study published 14 September 2018 in Nature’s Scientific Reports that enlisted the intriguing Rubber Hand Illusion technique and deep brain stimulation to investigate impaired motor function in Parkinson’s disease.

The mysterious functions of the basal ganglia

by Professor Dominic Thyagarajan

In 1982, the highly creative neuroscientist David Marsden delivered the Robert Wartenberg lecture to the American Academy of Neurology entitled "The mysterious motor function of the basal ganglia". In the lecture, he summarised almost 100 years of research into the function of these islands of neurons situated at the base of the brain. Although Marsden concluded the basal ganglia were concerned with the automatic execution of learned motor plans, he discussed speculations that extensive input to the basal ganglia of visual, auditory olfactory and sensory information, coming from wide areas of the cerebral cortex and thalamus and from the midline nuclei raphe nuclei concerned with wakefulness, indicated a function for these nuclei in perception, cognition and the focus of attention on environmental events.

Despite this, it is mainly the motor functions of the basal ganglia that have attracted the attention of researchers. Marsden also observed that Parkinson's disease, in which destruction of dopaminergic projections alters basal ganglia circuitry, is the 'test bed' against which theories of basal ganglia function should be measured.

In our study, we opportunistically investigated basal ganglia functions in perception and bodily awareness by turning deep brain stimulators on and off in a group of surgically treated patients with Parkinson's disease. In a previous study published in the journal Neuropyschologia (Volume 97, March 2017, pages 38-45) we used the Rubber Hand Illusion experiment to show that people with Parkinson's disease have illusory perceptions concerning body ownership under conditions which do not normally trigger this strange perceptual illusion in which people, under certain conditions of stroking, seem to feel that a fake rubber hand placed next to them actually belongs to them. We had provided evidence that Parkinson's disease, and by extension basal ganglia circuits, modulates the integration of sensory information from different modalities (vision, touch) to affect how a person perceives ownership of body parts.

In the present study in Scientific Reports, we not only confirmed our previous observations in Parkinson's disease, but were also able to show that deep brain stimulation, which is used to treat impaired motor function in Parkinson’s disease, also partially normalises the disturbed bodily awareness in the disease. Our study did not necessarily address how this could benefit patients treated with deep brain stimulation in their day-to-day life, but it does contribute to knowledge concerning the complex impairments of brain function in Parkinson's disease and the "Mysterious perceptual function of the basal ganglia".

Reference:
Catherine Ding, Colin J. Palmer, Jakob Hohwy, George J. Youssef, Bryan Paton, Naotsugu Tsuchiya, Julie C. Stout & Dominic Thyagarajan. Deep Brain Stimulation for Parkinson’s disease changes perception in the Rubber Hand Illusion. Scientific Reports Volume 8, Article number: 13842 (2018)

To read more about David Marsden https://www.independent.co.uk/arts-entertainment/obituary-professor-david-marsden-1179588.html