Abstract
The present article reports the results of a systematic review on the potential benefits of the combined use of virtual reality (VR) and non-invasive brain stimulation (NIBS) as a novel approach for rehabilitation. VR and NIBS are two rehabilitation techniques that have been consistently explored by health professionals, and in recent years there is strong evidence of the therapeutic benefits of their combined use. In this work, we reviewed research articles that report the combined use of VR and two common NIBS techniques, namely transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS). Relevant queries to six major bibliographic databases were performed to retrieve original research articles that reported the use of the combination VR-NIBS for rehabilitation applications. A total of 16 articles were identified and reviewed. The reviewed studies have significant differences in the goals, materials, methods, and outcomes. These differences are likely caused by the lack of guidelines and best practices on how to combine VR and NIBS techniques. Five therapeutic applications were identified: stroke, neuropathic pain, cerebral palsy, phobia and post-traumatic stress disorder, and multiple sclerosis rehabilitation. The majority of the reviewed studies reported positive effects of the use of VR-NIBS. However, further research is still needed to validate existing results on larger sample sizes and across different clinical conditions. For these reasons, in this review recommendations for future studies exploring the combined use of VR and NIBS are presented to facilitate the comparison among works.
Background
Virtual reality (VR) is a medium that is typically composed of an interactive computer simulation which detects the actions and position of the subject, additionally, it replaces or augments the feedback (e.g., visual, auditory, haptic) to the user, providing a sensation of presence in the simulation [1,2,3]. The last decade has witnessed a drastic improvement in computer graphics and computational power, which in turn, have paved the road to more realistic virtual- and augmented-reality systems and experiences, with applications in entertainment, gaming, e-commerce, architecture, interior design, manufacture, education, health and medicine [4]. Regarding rehabilitation, there is strong evidence supporting the use of VR therapy [5,6,7] in the treatment of pain, phobias, post-traumatic stress disorder (PTSD) [5], eating disorders [8], mental disorders, such as anxiety, schizophrenia and autism [9], and chemical abuse [10]. Moreover, VR has proven to be an important tool for exposure therapy [11]. Interestingly, a recent review on the medical literature has revealed that no reports of photosensitive epilepsy evoked by the use of VR headset [12].
Non-invasive brain stimulation (NIBS) techniques, in turn, have been consistently studied in the treatment of neuropsychiatric diseases as methods to modify or modulate the cortical excitability [13], and plasticity in the cerebral cortex [13, 14]. The two most common techniques used for NIBS are transcranial magnetic stimulation (TMS) and transcranial electrical stimulation (tES). As the name suggests, TMS uses magnetic fields, more specifically, their rapid change to induce a short pulse of electric current on the cortex, which in turn generates action potentials with a depth up to 5 cm. The application of the magnetic fields is carried out by a magnetic coil that is placed near the scalp over the cortical region of interest. TMS can be used in different ways, as single-pulse, repetitive TMS pulses (rTMS) [15, 16], or intermittent theta burst stimulation (iTBS) when magnetic pulses are intermittently applied in a specific burst [17]. NIBS with TMS have been used for the treatment of depression and schizophrenia [18, 19], pain [18], obsessive–compulsive disorder, Parkinson’s disease, epilepsy, task-related dystonia, and tic disorders [19]. On the other hand, tES relies on the passage of a weak electric current between electrodes placed on the scalp, thus stimulating the brain tissues between the electrodes. Depending on the type of electric current that is used, tES can be further divided into transcranial direct current stimulation (tDCS), alternating current stimulation (tACS), and random noise stimulation (tRNS) [20]; with tDCS being the most common type [14]. As tDCS possesses polarity, it can be anodal or cathodal, thus depolarizing or hyperpolarizing the resting membrane potential, respectively. This is reflected as an increase or decrease on the cortical excitability, respectively [20, 21]. Reported therapeutic applications of tDCS include treatment of pain, Parkinson’s disease, Alzheimer’s disease, motor disorders, stroke, aphasia, multiple sclerosis, epilepsy, depression, schizophrenia, and substance abuse [13]. In studies using TMS and tES, a “sham” (placebo) condition is often used as control. For tES, the sham condition consists in administering real tES to the subject during only few seconds at the beginning of the experiment to mimic the perception and experience of real stimulation. In TMS, there are two approaches for the sham condition: in one approach a TMS coil is placed in a position and orientation that evokes the somatosensory effects of real TMS but brain stimulation is absent; on the other approach, a sham TMS coil that resembles a regular TMS coil but is equipped with a magnetic shield that attenuates the magnetic field, additionally, electrical stimulation can be used to replicate the somatosensory effects of real TMS [22].
Recently, evidence has emerged showing promising therapeutic applications for the combined use of VR and tES (more specifically tDCS) [23,24,25,26], as well as VR and TMS [27,28,29], with outcomes not achievable by using either technique individually. Despite the reported promising results, the literature still lacks a systematic review covering the reported methods, outcomes, and potential therapeutic applications in neurological rehabilitation, on the combination of VR and NIBS techniques. This review aims to fill this gap, by reporting, comparing, and discussing studies that used VR-NIBS therapy for rehabilitation applications. Moreover, this review provides recommendations for future studies in the field to facilitate their development and comparison.[…]
TBI Rehabilitation 