Virtual Reality Tools for Assessing Unilateral Spatial Neglect: A Novel Opportunity for Data Collection

Summary

The goal was to design, build, and pilot a novel virtual reality task to detect and characterize unilateral spatial neglect, a syndrome affecting 23-46% of acute stroke survivors, expanding the role of virtual reality in the study and management of neurologic disease.

Abstract

Unilateral spatial neglect (USN) is a syndrome characterized by inattention to or inaction in one side of space and affects between 23-46% of acute stroke survivors. The diagnosis and characterization of these symptoms in individual patients can be challenging and often requires skilled clinical staff. Virtual reality (VR) presents an opportunity to develop novel assessment tools for patients with USN.

We aimed to design and build a VR tool to detect and characterize subtle USN symptoms, and to test the tool on subjects treated with inhibitory repetitive transcranial magnetic stimulation (TMS) of cortical regions associated with USN.

We created three experimental conditions by applying TMS to two distinct regions of cortex associated with visuospatial processing- the superior temporal gyrus (STG) and the supramarginal gyrus (SMG) - and applied sham TMS as a control. We then placed subjects in a virtual reality environment in which they were asked to identify the flowers with lateral asymmetries of flowers distributed across bushes in both hemispaces, with dynamic difficulty adjustment based on each subject's performance.

We found significant differences in average head yaw between subjects stimulated at the STG and those stimulated at the SMG and marginally significant effects in the average visual axis.

VR technology is becoming more accessible, affordable, and robust, presenting an exciting opportunity to create useful and novel game-like tools. In conjunction with TMS, these tools could be used to study specific, isolated, artificial neurological deficits in healthy subjects, informing the creation of VR-based diagnostic tools for patients with deficits due to acquired brain injury. This study is the first to our knowledge in which artificially generated USN symptoms have been evaluated with a VR task.

Introduction

Unilateral spatial neglect (USN) is a syndrome characterized by inattention to or inaction in one side of space that affects between 23-46% of acute stroke survivors, most commonly involving injury to the right cerebral hemisphere and resulting in a tendency to ignore the left side of space and/or the survivor's body^1,2. Although the majority of patients with USN experience significant recovery in the short term, subtle USN symptoms often persist³. USN can increase patient risk for falls and impede activities of daily living^2,4

Protocol

This study was approved by the local Institutional Review Board and meets all criteria set forth by Good Clinical Practice Guidelines. All participants provided informed consent before any study procedures began. Study participants were expected to participate in three separate sessions (outlined in Table 1). The elements of the experiment are described in stepwise fashion below. Session order was randomized.

Discussion

We successfully induced and measured USN symptoms with TMS and VR, respectively. While we did not have significant results when compared to sham trials, we were able to compare multiple metrics of egocentric neglect (average head angle, time spent looking at flowers in either hemispace) and allocentric neglect (performance in selecting flowers with asymmetric petals on the left vs. the right side) between the different experimental groups, and found significant differences in average head angle between subjects stimulate.......

Materials

Name	Company	Catalog Number	Comments
AirFilm Coil (AFC) Rapid Version	Magstim	N/A	Air-cooled TMS coil
Alienware 17 R4 Laptop	Dell	N/A	NVIDIA GeForce GTX 1060 (full specs at https://topics-cdn.dell.com/pdf/alienware-17-laptop_users-guide_en-us.pdf)
BrainSight 2.0 TMS Neuronavigation Software	Rogue Research Inc	N/A	TMS neural targeting software
CED 1902 Isolated pre-amplifier	Cambridge Electronic Design Limted	N/A	EMG pre-amplifier
CED Micro 401 mkII	Cambridge Electronic Design Limted	N/A	Multi-channel waveform data acquisition unit
CED Signal 5	Cambridge Electronic Design Limted	N/A	Sweep-based data acquisition and analysis software. Used to measure TMS evoked motor responses.
HTC Vive Binocular Add-on	Pupil Labs	N/A	HTC Vive, Vive Pro, or Vive Cosmos eye tracking add-on with 2 x 200Hz eye cameras.
Magstim D70 Remote Coil	Magstim	N/A	Hand-held TMS coil
Magstim Super Rapid 2 plus 1	Magstim	N/A	Transcranial Magnetic Stimulation Unit
Unity 2018	Unity	N/A	cross-platform VR game engine
Vive Pro	HTC Vive	N/A	VR hardware system with external motion sensors; 1440x1600 pixels per eye, 90 Hz refresh rate, 110° FoV