According to various sources of evidence, the frontal/striatum areas have a key role in the psychopathology of the brain's executive and functional disorders. In these areas, abnormal structure and/or function can create inattention and distraction, which are identified as ADHD symptoms^8,9). ADHD is a neuro-developmental disorder that is characterized by inattention, hyperactivity, and impulsivity^10,11). According to the Diagnostic and Statistical Manual of Mental Disorders, 4th edition, ADHD is one of the most common psychiatric conditions^1,12) and according to the Center for Disease Control and Prevention, this condition represents a public health issue, which is one of the most common functional disorders in childhood, with a 5%–9% prevalence rate¹³⁾. Almost 5% of school-age children are affected by ADHD and their behavioral competencies in many aspects are poorer compared to their normal peers¹⁴⁾. The symptoms experienced by these children may improve^3,14). Nevertheless, ADHD symptoms may develop and affect children in their daily functioning, social behaviors, interpersonal relationships, and education^3,5). Currently, the rehabilitation of children with ADHD includes psychological counseling, medication, and behavioral therapies^6,15,16).

Virtual reality, which is also known as computer-simulated reality or video-generated environments, is a computer technology that simulates an imagined or real environment such as a classroom^17,18). By using this technology, users can interact in 3-dimensional environments and behave as they would in the real world¹⁹⁾. The application of this technology has emerged in educational and training, entertainment, military, medical and surgical areas^17,20,21). Immersive VR, desktop VR, projective VR, and CAVE (C-Automatic Virtual Environment) are the most used types of virtual reality. The ability of this technology is based on the quick construction of different life-like environments for training and for controlling irritants^3,22,23). The development of VR systems offers numerous advantages such as creating an environment that meets the patient's requirements, providing stability between users and stimuli, as well as providing a complete record of patients' behaviors and functionalities, facilitating rapid feedback and time and cost savings, and delivering a more entertaining tool to motivate patients use this technology^3,22). In the rehabilitation domains, VR technologies allow people with impairments and disabilities related to brain damage to experience anything that is difficult or impossible for them in reality^24,25).

Health guidelines list possible side effects of VR ranging from headaches, seizures, nausea, fatigue, drowsiness, disorientation, apathy, and dizziness. These symptoms are related to cybersickness or virtual reality sickness, which can endanger health and safety, as well as the effectiveness of VR. Cybersickness as a complex problem is the psychophysiological answer to exposure to VR environments^26,27). Studies have indicated that cybersickness is a barrier to the use of training or rehabilitation tools in virtual reality environments^28,29). Therefore, cybersickness can be prevented or managed by understanding its causes and factors that influence its incidence²⁶⁾. Depending on the VR system type, the purpose of the tasks, and the characteristics of the individual user, a variety of measures may be taken to fix or manage VR's side effects. Studies have indicated several methods to prevent cybersickness, including correct calibration of a VR system, adaptation and customization according to users' needs, enabling a more natural user interface (UI) and using haptic interfaces, making the head-mounted display (HMD) lighter, as well as ensuring moderate usage of a VR system^26,29,30,31).

Virtual reality has the ability to render some neuropsychological tests, such as the continuous performance test (CPT), of cognitive processes, including attention, memory, and executive function, in a more reliable way^32,33). Pollak et al.³⁴⁾ reported that CPT embedded in VR (VRC-CPT) has higher ecological validity and that children with ADHD prefer VRC-CPT over classic CPT. In addition, the studies of Adams et al.³⁵⁾ and Díaz-Orueta et al.³⁶⁾ have confirmed these results and suggested that VRC-CPT testing is a suitable tool to assess the symptoms of ADHD in children. VR combined with interactive tests, by providing specific stimuli, can remove distractions and hold patients' attention and concentration for a long time and can also be helpful in the rehabilitation of children with ADHD^3,22,37,38). Recently, using VR technologies as computer graphics for simulating the real world have reduced the malfunction of patients in their daily life^39,40) in that knowledge gained from VR can be transmitted to a real environment⁴¹⁾. Virtual reality environments make it possible to observe individuals' behavior and detect their cognitive deficits³⁴⁾.

Numerous studies confirmed the advantages of virtual reality in cognitive performance, such as working memory, executive function, and attention^32,42,43,44). Deficits in attention, as a main cognitive process, are common and a major disability for persons with ADHD. Studies have indicated the potential of VR in the assessment and training of attention without any distractions^33,45,46). They have demonstrated that, when participants with ADHD performed cognitive tasks targeted on attention assessment through VR use, they obtained better scores than when using traditional techniques²²⁾. Rizzo et al.³²⁾ designed a VR classroom to assess attention performance. In their study, participants used a HMD to solve tasks while visual and auditory stimuli were presented. Since participants with ADHD make many mistakes and excessive body movements in their tasks, other studies showed the significant role of virtual reality in improving these conditions and reducing behavioral symptoms and problems^{3,14,25,33,39,47)}. Moreover, the study of Pollak et al.⁴⁸⁾ showed that, methylphenidate reduced omission errors and reaction time variability with VR-CPT compared to without VR-CPT. Furthermore, this technology has an effective role in safe training programs and enhancing academic performance for these patients, whereas these programs in real life may be dangerous, difficult, or costly¹⁷⁾. The present article investigated numerous studies that have used various types of virtual reality technologies, such as virtual classroom, virtual gaming, and virtual reality traffic gap-choice, for diagnosis, monitoring, evaluation, treatment, and training of 6- to 18-year-old children with ADHD^{14,15,33,49,50,51,52)}. Table 1 presents a brief description of these finding including the aim of study, characteristics of patients with ADHD, VR technology types, and results.