Spatial memory recovery in neurorehabilitation using VR

Authors: Victor Dabala, Oana Vanta

Keywords: spatial memory,  neurorehabilitation, virtual environment

A different type of environment for spatial memory recovery in neurorehabilitation 

Virtual reality (VR) has been considered a pinnacle of technological advances since its first applications. VR, which could be summarized as an immersion into a computer-generated environment, has been successfully implemented in various fields of interest, one of them being clinical medicine and interconnected domains. For example, VR was previously used for neurorehabilitation in the field of cerebrovascular diseases, with examples indicating satisfying results for ischemic stroke, spatial memory deficits, traumatic brain injury (TBI), or the spectrum of anxiety and depression conditions [1–4].

For neurorehabilitation, the core principle of VR is, therefore, the establishment of a virtual environment (VE) created in relationship with the complex necessities of patients. For a VR and VE to be efficient, the neurological patient has to be given the feeling of familiarity with the novel surroundings (the sensation of being present in a place that is not considered a part of the self). Moreover, the visual interface, which creates the respective feeling, will deliver most of the inputs to the system. It could be considered that between the system and the subject, there is a bilateral relationship, as the information from the VE will transform the patient’s perception and compensate for eventual losses, while the patient’s data will improve and optimize the overall experience [1].

Virtual Reality and Environments are considered a suitable and enjoyable solution for most patients, as a high adherence can be observed in the neurological population. The safety profile can also be described in good terms, as many trials did not report any adverse effects. However, certain unpredicted situations can be encountered, with cybersickness being a significant complaint (nausea, headaches, impaired vision over time, or vomiting) (Figure 1). Falls, especially in a poorly controlled environment, are also considered an issue [1, 5].

Figure 1. Cybersickness effects

VE as a substitution for more specific conditions – Spatial Memory deficits

Besides the increased adherence of patients, the use of VEs has other significant benefits, as showcased in Figure 2 [1].

Figure 2. Benefits of VEs

A particular group of patients that could be suitable for VR/VE rehabilitation are subjects with impairments in navigational and acclimatizational functions. As a result, the function of spatial memory can be considered the target in this specific population [1].

Two areas closely related to spatial memory (SM) formation are the hippocampus and the mesial temporal lobe. The primary mechanism of action regarding SM is the generation of allocentric renditions constructed on environmental stimuli. Both regions are part of an integrated network that operates spatial memory formations, a network in which other areas take part:

• The parietal lobe
• The retrosplenial cortex
• The parieto-occipital sulcus [1, 2].

 Therefore, lesions caused by the structures above generate different alterations regarding superior cognitive functions, especially spatial memory [6].

A systematic literature review (SLR) by Montana et al. [1] investigated the utility of VR in SM impairment in comparison to the classical treatment methods. The outcomes that were followed focused on:

• Identifying the devices that are most suitable for neurorehabilitation
• The implementation of VR/VE in different clinical backgrounds
• A direct comparison between the analyzed methodologies to determine which has the most advantages [1]. 

The elaboration of the systematic review respected the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, including the following types of scientific papers: Randomized control trials (RCT), Non-randomized control trials, Intervention studies, and Case-control studies [1].

All the studies included had to assess spatial memory with virtual reality equipment in carefully controlled environments. Studies that focused on the navigational abilities of patients with stroke, Alzheimer’s disease (AD), multiple sclerosis, epilepsy, cerebral palsies, neglect, or topographical disorientation were considered viable for inclusion (Figure 2). At the end of the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) process and an evaluation for bias risk – respecting the STROBE (STrengthening the Reporting of OBservational studies in Epidemiology) statement -, 16 studies were selected as proper material [1].

Nine labels were created for the assessment of each article, of which the model of the VR, the task assigned to the subject, and the instrument used for neuropsychological evaluation were the most important [1].

Technological competition for an improved outcome

A specific type of VE can generate multiple versions of a virtual environment based on the available equipment. Considering this premise, the SLR by Montana et al. compared the level of virtual immersion that each type of equipment could generate. As a result, the HMD Oculus Rift DK2 [Figure 3] was considered the optimal solution for a full immersion into VE [1, 7].

Figure 3. The HMD Oculus Rift DK [8]

• The OctaVis (semi-immersion) – Consists of eight different screens, which the subject can access by simply rotating in a specially built chair
• The Nirvana PC System (semi-immersion) – Infrared-based VR used a screen projector to create the VE.
• NeuroVR (non-immersive) – Cost-effective VR modality for fine-tuning previously created virtual environments. This VR was associated with the British developer Superscape, which specializes in video games [Figure 4].
• VRSS (Virtual Reality Rehabilitation System) – Based on a connection between central and peripheral pieces of equipment, this VR model uses a generated magnetic field for detecting the motion 
• Other non-immersive techniques tried to replicate a non-fictional setting, such as different towns around Europe (e.g., London or Graz) [1, 7, 9].

Figure 4. Screenshot of a sequence integrated with the NeuroVR type 2 software [10]

Because of the headset-integrated component, fully immersive therapies represented the most suitable option for elevating spatial and attentional disorders, followed by the semi-immersive type. The non-immersive modalities were demonstrated also to be a good possibility, targeting dysfunctionalities of navigation. The feeling of “presence,” highlighted previously in the paper, is the primary reason for the superiority of fully immersive virtual environments. The second advantage is the complex feedback delivered to the patient (through a custom avatar or using the head-up display – HUD of the headset component) [1,7].

See also the article: Can gaming therapy impact post-stroke rehabilitation?

Tailoring the proper virtual environment at the individual level

Five parameters were considered for a proper spatial memory rehabilitation session:

• The total time spent by each patient in the virtual environment
• The rate of sessions per unit of time
• The intensity that the virtual environment stressed on each patient
• The time interval that has passed since the patient suffered the injury that generated the navigational deficit
• Construction of an environment that closely resembles the real world or a situation in which the user will feel familiar [1–7, 9].

Regarding the duration of the intervention, decided by each investigator of the 16 studies, two randomized controlled trials demonstrated a linear relationship between the total time spent in the virtual environment and the improvement in spatial memory. To ensure the stability of the aforementioned relationship over long periods of time, the investigators assessed patients at two-time points (two months follow-up, respectively 1 year after the end of the intervention) [9, 11]. This is strengthened by results offered by a different trial, in which patients underwent only four VR/VE therapy sessions. The outcome was described as favorable in only one patient, further extending the role that a prolonged treatment has [12].

A different linear relationship with time was demonstrated in the case of therapy onset. The superior cognitive functions were recovered faster if the patient was enrolled one year after the injury had passed. The principle was demonstrated in both traumatic brain injury and stroke patients [9, 13].

While in the virtual environment, each subject had several tasks to be accomplished. Each task was created in a manner that could facilitate the training of spatial memory. Across the 16 studies, patients had to either focus only on the task or accomplish both the task and explore the surroundings. While the second action was not mandatory, it was reported that an increased synergy was obtained if the user roamed freely around the environment (e.g., a virtual copy of a city). Examples of implicit tasks that were introduced are “Cut all the trees that you encounter”, “Find a certain object (e.g., a window of a building)”, or “Go to a certain place”. Other studies focused on the patient’s capability of avoiding repeated patterns, like not exploring the same area twice in the same session [9, 14].

Finally, the most suitable outcome measurements had to be identified across the sixteen studies. While some instruments were previously used in clinical practice (e.g., the Supraspan Corsi Test or Montreal Cognitive Assessment – Moca), others were created for the sole purpose of the RCT (the locally created Virtual Tubingen Test). Each test was adequately adjusted for the generated virtual actions (e.g., assessing the correct and complete number of products bought in a virtual supermarket). The Rey Auditory Verbal Learning Test (RAVLT) demonstrated the fixation of improvements in spatial memory at one-year follow-ups [1, 7, 9, 13, 14].

Other scales used include the following:

• Benton Visual Retention Test (BVRT)
• Achievement Measure System LSP 50+
• Visual Pursuit Test
• Bergen Right-Left Discrimination Test (BRLD-B)
• Rey-Osterrieth Complex Figure (ROCF).

Spatial memory recovery in neurorehabilitation | what should be done to turn VR into a standard therapy?

Assessing sixteen studies, the systematic review by Montana et al. demonstrated that virtually generated environments could represent an important option for clinicians in the field of neurorehabilitation. Taking into consideration that not all the studies included were controlled trials and those that were RCTs referred to a limited number of patients, further scientific works should focus on large-scale studies in which multiple VR equipment types could be compared, each one generating a different environment with a specific navigational task assign. Limitations like a proper control group, cost-effectiveness, or complexity of several VR systems are other parameters that should be considered in the near future.

Spatial memory impairment affects how patients can adequately understand and navigate a particular environment. While the previously encountered disadvantages of cognitive function recovery cannot guarantee a high rate of success (reduced adherence, serious adverse effects, or improper fixation of improvements over long periods), virtual reality and virtually-generated environments could bypass all the previously mentioned problems by simply inviting the patient to experience a journey into the virtual realm, all at the cost of adequately applied technology.

References

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