An overview as seen in the Neuroscience of Virtual Reality: From Virtual Exposure to Embodied Medicine [1]

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Why is VR so effective? Here, the following answer is suggested: VR shares with the brain the same basic mechanism—embodied simulations.

An increasingly popular hypothesis—predictive coding [2,3,4]—suggests that the brain actively maintains an internal model (simulation) of the body and the space around it, which provides predictions about the expected sensory input and tries to minimize the amount of prediction errors (or “surprises”). An in-depth discussion of these concepts is not offered here because authoritative and thorough accounts have been provided elsewhere. [2-7] However, herein, the focus is on the concept of simulation introduced by this paradigm to understand better the links between the brain and VR.

One of the main tenets of predictive coding is that to regulate and control the body in the world effectively, the brain creates an embodied simulation of the body in the world. There are two main characteristics of this simulation. First, different from other internal models used in cognitive science—such as Tolman’s cognitive maps or Johhson–Laird’s internal models—they are simulations of sensory motor experiences. In this view, they include visceral/autonomic (interoceptive), motor (proprioceptive), and sensory (e.g., visual, auditory) information. Second, embodied simulations reactivate multimodal neural networks, which have produced the simulated/expected effect before. To regulate and control the body in the world effectively, the brain creates an embodied simulation of the body in the world used to represent and predict actions, concepts, and emotions. Specifically, it is used to predict: (a) upcoming sensory events both inside and outside the body, and (b) the best action to deal with the impending sensory events.[8]

VR works in a similar way: the VR experience tries to predict the sensory consequences of the individual’s movements, providing to him/her the same scene he/she will see in the real world. To achieve this, the VR system, like the brain, maintains a model (simulation) of the body and the space around it. If presence in the body is the outcome of different embodied simulations, and VR is a simulation technology, this suggests the possibility of altering the experience of the body by designing targeted virtual environments.[9] In this view, VR can be defined as an “embodied technology” for its possibility of modifying the embodiment experience of its users.[10,11,12] As noted by Riva et al., “using VR, subjects can experience the synthetic environment as if it was ‘their surrounding world’ (incarnation: the physical body is within a virtual environment) or can experience their synthetic avatars as if they were ‘their own body’ (embodiment: the physical body is replaced by the virtual one).”13(p9) In other words, VR is able to fool the predictive coding mechanisms used by the brain generating the feeling of presence in a virtual body and in the digital space around it.

As underlined by Barrett, in The Theory of Constructed Emotion, “The brain constructs meaning by correctly anticipating (predicting and adjusting to) incoming sensations. Sensations are categorized so that they are (a) actionable in a situated way and therefore (b) meaningful, based on past experience. When past experiences of emotion (e.g., happiness) are used to categorize the predicted sensory array and guide action, then one experiences or perceives that emotion (happiness).”8(p9) In this view, the feeling of presence in a space can be considered as an evolutive tool used to track the difference between the predicted sensations and those that are incoming from the sensory world, both externally and internally. [14-16]

VR works in a similar way: it uses computer technology to create a simulated world that individuals can manipulate and explore as if they were in it. In other words, the VR experience tries to predict the sensory consequences of your movements, showing to you the same scene you will see in the real world. Specifically, VR hardware tracks the motion of the user, while VR software adjusts the images on the user’s display to reflect the changes produced by the motion in the virtual world. To achieve it, like the brain, the VR system maintains a model (simulation) of the body and the space around it. This prediction is then used to provide the expected sensory input using the VR hardware. To be realistic, the VR model tries to mimic the brain model as much as possible: the more the VR model is similar to the brain model, the more the individual feels present in the VR world. [14, 17]

Moseley et al. suggested that these simulations are integrated with sensory data in the “body matrix,” a coarse supramodal multisensory representation of the body and the space around it. [18-20] Specifically, the contents of the body matrix are defined by top-down predictive signals, integrating the multisensory (motor and visceromotor) simulations of the causes of perceived sensory events. [21] The different simulations are then ranked and included in the body matrix according to their relevance for the intentions of the self (selective attention). At the same time, the content and the priority of the different simulations are corrected by bottom-up prediction errors that signal mismatches between predicted and actual contents of sensory events.[22]

At the end of this process, the body matrix defines where the self is present, that is, in the body that our brain considers as the most likely to be its one. [23-25] As underlined by Apps and Tsakiris, “The mental representation of the physical properties of one’s self are, therefore, also probabilistic. That is, one’s own body is the one that has the highest probability of being ‘me,’ since other objects are probabilistically less likely to evoke the same sensory inputs. In short, the notion that there is a ‘self’ is the most parsimonious and accurate explanation for sensory inputs.”23(p88)

According to neuroscience, the body matrix [18,19, 26, 27] serves to maintain the integrity of the body at both the homeostatic and psychological levels by supervising the cognitive and physiological resources necessary to protect the body and the space around it. Specifically, the body matrix plays a critical role in high-end cognitive processes such as motivation, emotion, social cognition, and self-awareness, [28-30] while exerting a top-down modulation over basic physiological mechanisms such as thermoregulatory control [31, 32] and the immune system.[27]

In this view, different authors [10,12, 33, 34] have recently suggested that an altered functioning of the body matrix and/or its related processes might be the cause of different neurological and psychiatric conditions. If this is true, VR can be the core of a new trans-disciplinary research field—embodied medicine [11, 12]—the main goal of which is the use of advanced technology for altering the body matrix, with the goal of improving people’s health and well-being.

VR compares favorably to existing treatments in anxiety disorders, eating and weight disorders, and pain management, with long-term effects that generalize to the real world. The most common use of VR in behavioral health is for exposure therapy (VR exposure [VRE]). VRE is similar to classic exposure therapy [35, 36, 37] — the patient is exposed to a graded exposure hierarchy—with the only difference being that VR is substituted for other exposure techniques (e.g., in vivo or imaginal exposure). In the treatment of complex anxiety disorders, the use of VRE is often combined with other techniques such as breathing or relaxation exercises,[38] attentional and autonomic control training,[39] biofeedback,[40, 41] and/or cognitive restructuring.[42]

Available data show that VR is able to reduce anxiety symptoms significantly in different anxiety disorders: phobias,[43] post-traumatic stress disorders,[44] panic disorder and agoraphobia,[45] social anxiety disorders,[46] psychological stress,[47]and generalized anxiety disorders.[48] Another article specifically explored the use of VR for the assessment of psychiatric disorders, [49] finding that virtual worlds are able to induce and assess psychiatric symptoms simultaneously, with significant correlations between VR measures and traditional diagnostic tools. Moreover, VR is also effective in assessing cue reactivity[50]: its use is able to increase subjective craving in smokers,[51, 52] alcohol drinkers,[53] eaters,[54] and cocaine-dependent individuals.[55]

Body swapping, [is a technique which] replaces the contents of the bodily self-consciousness with synthetic ones (synthetic embodiment). This has been used in eating and weight disorders to improve the experience of the body in both clinical (anorexia and morbid obesity) [56, 57] and non-clinical subjects.[58-60] Nevertheless, the potential of this approach is wider. [61] For example, it may offer a non-pharmacological way to reduce chronic pain. Nevertheless, according to Tsay et al., “available findings present compelling evidence for a novel multisensory and multimodal approach to therapies for chronic pain disorders”62(p249) In this view, the use of VR embodiment may offer new treatment options for pain management. [63-65] Some studies have suggested the possibility of using VR body swapping to improve body perception disturbance in patients with complex regional pain syndrome. [66, 67]

An emerging approach is the use of VR to augment the bodily experience through the awareness of internal (and difficult to sense) bodily information, or the mapping of a sensory channel to a different one—for example vision to touch or to hearing (augmented embodiment).[68, 69] For example, Suzuki et al.[70] implemented an innovative “cardiac rubber hand illusion” that combined computer-generated augmented reality with feedback of interoceptive information. Their results showed that the virtual-hand ownership is enhanced by cardio-visual feedback in time with the actual heartbeat, supporting the use of this technique to improve emotion regulation. The first outcome of an integrated VR platform able to simulate both the external and the inner world is the possibility of structuring, augmenting, and/or replacing all the different experiential aspects of bodily self-consciousness.

The final long-term outcome of this possibility may be the embodied virtual training machine described by the science-fiction thriller The Matrix. In this movie, the heroes, Trinity and Neo, learned how to fight martial-arts battles and drive motorcycles and helicopters by experiencing the bodily processes and concepts related to the skill through an embodied simulation.

The long-term goal of the vision presented in this article is the use of simulative technologies—both simulating the external world and the internal one—to reverse engineer the psychosomatic processes that connect mind and body. If achieved, this perspective will provide a radically new meaning to the classical Juvenal’s Latin dictum “Mens sana in corpore sano” (a healthy mind in a healthy body) by allowing a new trans-disciplinary research field—“Embodied Medicine”[11, 12]—that will use advanced multisensory technologies to alter bodily processes for enhancing homeostasis and well-being.

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