During the course of the project, we have created an innovative VR-based setup for inducing sensory-motor adaptation. In this setup, participants had to catch dynamic targets (tennis balls) with a virtual hand. After several trials, the virtual hand shifted laterally with respect to the participants' own hand, forcing participants to adapt their reaching movements in the direction opposite the shift in order to catch the tennis balls (Figure 1). We used this setup to induce a brief adaptation training for healthy individuals and long-term rehabilitation training with neglect patients. We have published a paper describing the VR-adaptation setup and its behavioural aftereffects (Wilf et al., 2020), and a clinical trial comprising our paradigm is about to be launched by our collaborators at ‘MindMaze’ biotechnology company to test effectivity of rehabilitation of stroke survivors and neurological patients with spatial deficits at the Lausanne University Hospital.
In order to unravel the neural aftereffects of our VR-adaptation training, we recorded brain activity under identical conditions before and after adaptation experience using neuroimaging methods. Brain activity was recorded under several conditions:
1) Free viewing of a sequence of short naturalistic videoclips.
2) Spontaneous brain activity while participants rest with their eyes closed.
We found that when healthy individuals were watching naturalistic videos following VR-adaptation with a rightward shift, activity in their right hemisphere visual cortex was enhanced as compared to following VR training with no shift. Since right visual cortex processes visual information from the left portion of space, this effect reflects enhanced visual representation of the left portion of space following VR-adaptation. Furthermore, the amount of right hemisphere activity enhancement was strongly correlated with the amount of behavioural aftereffects measured in our group of participants, suggesting a link between behavioural and brain modulation induced by VR-adaptation experience.
We next explored the effect of adaptation on spontaneous brain activity without task or sensory stimulation. To validate our VR setup, we initially measured the change in spontaneous activity following exposure to prism adaptation goggles outside VR. We discovered that prism adaptation modulated the connections between large-scale functional brain networks – namely the networks controlling attention, and the network responsible for self-referential processes (Wilf et al., 2019). We then recorded spontaneous activity in three groups of healthy participants before and after VR training with either rightward shift, leftward shift, or no shift. We found that VR-adaptation again causes disconnections between large-scale networks in the cortex – the attention network and the self-referential network. Interestingly, the disconnection was more pronounced in the hemisphere contralateral to the shift induced (left hemisphere for rightward shift and right hemisphere for leftward shift) and between the hemispheres. The group who trained with no shift showed no modulation of spontaneous activity.
