Stroke & Body Ownership

Abstract

The feeling of ownership over a limb is a belief that is taken for granted. Unfortunately, some patients experience as if their hand or leg does not belong to themselves after suffering from a stroke. It is as yet unclear how to diagnose these impairments, what the underlying mechanism is and to what extent it can be influenced. This thesis investigated this phenomenon from a neuropsychological perspective. Body ownership impairments were objectified by an experiment in which body ownership was manipulated. On implicit and objective outcome measures, it was found that patients with body ownership impairments showed en enhanced susceptibility to manipulations of the body image, compared to healthy controls. This can be interpreted as if the demarcation between what belongs to them and what not, is weakened. Furthermore, it was found that impairments in left right orientation are associated with body ownership impairments. More specifically, patients with body ownership impairments and problems with identifying their fingers were more likely to be impaired on left right orientation test when mental rotation was required. Furthermore, we found that lesions to the right insula cortex were associated with impairments in mental rotation and left right orientation. These findings connects lines of research that show that spatial cognition might be related to body ownership, and that the insula cortex is important for mediating these functions. Finally, we discovered that affective, pleasant touch has an unique influence on body ownership as opposed to regular touch. Pleasant touch is conveyed by a specific kind of nerve fiber (CT fibers) which is activated when someone is stroked with a velocity around 3 cm/s on hairy skin. Pleasant touch is therefore processed differently in the peripheral nerves, but also in the brain. Interestingly, input from affective touch is processed by the right insula, the same brain area that is associated with body ownership impairment. In this thesis, we describe an experiment in healthy individuals that show that there is an enhanced body related illusion when the illusion is induced by affective touch compared to regular touch. This was specific for hairy skin (that contain CT fibers). This suggests that affective touch modulates body ownership. This is in line with observations of patients with body ownership impairments that show a tendency to caress their affected arm in a loving manner. These findings provide evidence that affective touch might be a promising candidate for relieving symptoms of body ownership impairments.