Virtual reality (VR) is a computer-based technology that allows users to interact with a multisensory simulated environment and receive “real-time” feedback on performance.

Most current VR systems are primarily visual experiences, using either a computer screen or special stereoscopic 3D screens (e.g., virtual reality room). Additional sound information is provided through speakers or headphones. Some advanced VR systems include haptic feedback technology that takes the advantage of the sense of touch by applying forces, vibrations, or motions to the user providing tactile information [9–12].

VR has been used in a wide variety of applications, including aeronautic and military training, architecture, sports, entertainment, art, and medicine. In the medical field, VR is being applied in rehabilitation, laser eye surgery, training for performing medical procedures (e.g., endoscopic or endovascular), and behavioral education (cognitive behavioral therapy) [9, 10, 13, 14].

VR applies relevant concepts in stroke rehabilitation, such as high repetition, high intensity, and task-oriented training of the paretic extremity [7, 15]. VR applications range from non-immersive to fully immersive depending on the degree to which the user is isolated from the physical surroundings when interacting with the virtual environment [15]. Also classified as VR are a variety of non-immersive video-game systems developed by the entertainment industry for home use, making this technology less costly and more accessible to clinicians and individuals. Several of these games have been adopted by clinicians as rehabilitation interventions even though they have not been especially designed to meet rehabilitation goals, nor validated in large randomized clinical trials.

Recovery depends on learning new strategies and motor patterns. Three important principles may be involved in motor recovery using virtual reality technologies: (1) brain plasticity, (2) “mirror-neuron system,” and (3) the “brain reward system.”

The presence of a hemiparetic limb may result in suppression of the cortical representation of the affected limb (i.e., hand) and further inhibit its spontaneous use [16]. Motor improvement can be achieved by the brain’s own ability to relearn and readjust. Repetitive, intensive, and task-specific functional training are the current paradigms applied in neurorehabilitation after stroke to facilitate motor relearning and consequently improvement of function [17, 18]. This is possible due to cortical reorganization and rewiring in the injured brain (brain plasticity) [16, 18]. Intense training and the observation, practice, and representation on the screen of task-specific activities can facilitate cortical reorganization. This is possible by engaging the “mirror neuron system” and/or long-term potentiation effects. The use of virtual reality showed practice-dependent enhancement of the affected arm through the facilitation of cortical reorganization using functional MRI [19]. These observations were also consistent with previous studies using transcranial magnetic stimulation and functional MRI that have demonstrated decreased ipsilateral cortical activation and increased contralateral activation as functions of intensive practice of the affected limb [20, 21]. A learning by imitation has been suggested to induce an imitation-dependent organization around the motor cortex through “mirror” neural networks [22]. Similarly, participants who received sensory feedback during the VR training learned the motor pattern by imitation. This might have facilitated use-dependent cortical plasticity, which was primarily reorganized at the supplementary motor cortex [19].

For example, a study including 154 healthy teenagers revealed morphological changes (e.g., thickening of grey matter) and activation of the ventral striatum using functional MRI among frequent (defined as more than 9 h per week) video-game players. The association of video-game playing with higher left ventral striatum volume could reflect altered reward processing and represent adaptive neural plasticity [23].

VR gaming technology has all the advantages of virtual reality systems including the provision of multisensorial (visual, auditory, and tactile) feedback, affordability, and easy implementation. Moreover, VR may engage the “brain reward system,” thus improving performance by optimizing or increasing patients’ motivation.

The brain reward system is a group of dopamine-mediated mesolimbic structures (nucleus accumbens and orbitofrontal circuits) that may be activated when participants play a video game. Some studies suggest an improvement of patients’ attitudes toward chemotherapy in healthy individuals immediately after the interactive gameplay. Using functional MRI, researchers found increased activation in several brain regions including a subregion of the left parahippocampal cortex. Another study including 18 health males found two different stimuli for the reward circuits: (1) reward-specific and (2) reward nonspecific networks. The anterolateral orbitofrontal cortex processes monetary gains, whereas the posterior lateral processes more basic erotic stimuli. Further studies may be needed to validate these findings [24].