The world population is expected to grow to 9.68 billion people by 2050 [25]. More importantly, the proportion of people aged 60 or older is expected to increase in the so-called “more developed countries” from currently 23 to 32 % of the total population by 2050 [32]. With neurological disorders such as stroke, Parkinson’s disease, or multiple sclerosis being more prevalent in older adults [1, 8, 30], our healthcare systems desperately need cost-efficient, widely available interventions that can address the cognitive and motor impairments of the aforementioned disorders and help reintegrate affected individuals in society.

Virtual rehabilitation technologies and interactive off-the-shelf games have seen increasing popularity in clinical settings over the past two decades [10, 14]. Virtual rehabilitation includes a wide array of applications that use virtual scenarios and environments for the purpose of clinical assessment and remediation. Available systems range from complex motion platforms, projection systems, tracking systems, and head-mounted displays to low-cost gaming consoles and motion-tracking sensors. Distinguishing factors of such systems are the use of fully virtual environments (i.e., virtual reality), real environments with an overlay of virtual information (i.e., augmented reality), or a mixture of both (i.e., mixed reality). Further, virtual rehabilitation setups can be immersive or non-immersive where immersive denotes systems in which three-dimensional scenarios are displayed and the user can change visual perspective through head movements (e.g., head-mounted displays or cave projection setups). On the contrary, non-immersive systems present virtual scenarios on a two-dimensional display (e.g., on a TV, laptop, or computer screen) with or without interface devices such as keyboard, computer mouse, or a joystick. Regardless of the actual hardware and software configuration, these approaches are often considered viable alternative or adjunct treatments to existing therapies, because of their motivational nature and precise control over feedback and task parameters.

This chapter focuses on the use of virtual rehabilitation systems for the treatment of motor deficits after stroke and traumatic brain injury. Recent advances of virtual reality hardware are being discussed and their potential for new rehabilitation systems along with strengths and weakness are being outlined. Moreover, relevant clinical trials and meta-analyses since the writing of the previous version of this chapter are summarized and their results discussed.

Virtual reality systems are often a heterogeneous set of input/output devices that can consist of a wide range of displays, tracking devices, controllers, and computer systems. Historically, such systems were almost exclusively associated with high costs, cumbersome, wired equipment, and a lack of compatibility between different devices and device drivers [27]. However, within the past two years virtual reality technology has seen a transformation toward low-cost components that are being developed and marketed for the rapidly growing video and computer game industry. Much of that growth is also driven by the rise of mobile computing and the availability of high-resolution mobile displays. Modern head-mounted displays have evolved from cumbersome, tethered devices to goggles that simply allow the user to attach an off-the-shelf smartphone and leverage the inbuilt motion sensors and cameras of the phone. Consequently, prices for head-mounted displays have dropped from tens of thousands to merely hundreds of dollars while image quality and tracking latency have improved tremendously. Examples of such new display solutions are the Oculus Rift,¹ Samsung Gear VR,² Avegant Glyph,³ Durovis Dive,⁴ Google Cardboard,⁵, or the Zeiss VR One.⁶ Most of these are still in alpha or beta prototype stage, but new innovative products are announced on a regular basis and should invigorate the competition further. A similar trend is evident for video game peripherals and 3D interaction devices which are mostly developed for console and computer game markets. New tracking devices such as the Microsoft Kinect 1 and 2,⁷ Leap Motion controller,⁸ Razer Hydra,⁹ Nimble Sense¹⁰, and treadmills such as the Virtuix Omni¹¹ and Cyberith Virtualizer¹² provide an affordable entry to naturalistic 3D interaction in virtual scenarios. All of these new competitors are of high importance to developers and researchers in the virtual rehabilitation field, as for the first time in the history of virtual reality technology, therapeutic systems have become affordable and accessible for use in the wider clinical setting, outside of the research laboratory. In addition, the development of virtual rehabilitation software has become much more accessible as game engines such as Unity,¹³ Unreal Engine 4¹⁴, and CryEngine 3¹⁵ are widely available for low monthly subscriptions or even for free. Each development tool comes with large communities of enthusiastic game developers who provide free assets, tutorials, and help on online forums and discussion groups. Virtual reality hardware companies have realized the potential of these large communities and provide free integrations of their devices and drivers for the most common game engines. All of these factors taken together provide an excellent ecosystem for the development of low-cost virtual rehabilitation systems that would have cost hundreds of thousands of dollars three to five years ago.

Innovative technologies such as virtual rehabilitation tools are being applied by using motor learning principles and taking advantage of neuroplasticity in order to compensate, restore, and recover loss of sensorimotor function occurring in stroke and traumatic brain injury patients. This section will outline the different factors that make virtual rehabilitation systems a suitable option for the treatment of sensorimotor deficits in neurorehabilitation and add value beyond traditional forms of treatment.