Abstract: Elderly people with mild cognitive impairment (MCI) is a high-risk group for dementia. However, their brains retain structural and functional plasticity. Virtual reality (VR) based training can help delay the progression of MCI towards dementia.
VR training can improve the overall cognitive function, especially memory, attention, and executive function of MCI elderly people. There is considerable variation in the results of current research as to whether the effects of VR training to improve cognitive function in older adults with MCI are equal to or superior to interventions in traditional settings. The effect of VR training is influenced by factors such as immersion level, training form, and task content. Increasing the level of immersion in the virtual environment in VR training can increase the number of user interactions with the environment, access more information available for processing, and improve task involvement. Reducing the level of immersion is effective in reducing screen-sickness symptoms, improving the safety and sustainability of training. Combined VR training that includes both physical and cognitive training can improve the cognitive function of older adults with MCI by improving their instrumental activities of daily living (IADL), and parallel training is more effective than serial training. VR training tasks are varied, personalized content settings for VR training tasks are more likely to help improve cognitive functioning in independent individuals. At the same time, improving the authenticity and timeliness of the details in the task situation and matching the cultural context can improve mission completion. The task content also needs to be more in line with the user's lifestyle. Adding appropriate game elements can enhance motivation, but the difficulty of operating the device, the number and complexity of operating instructions need to be considered to make it suitable for MCI elderly. In addition, different virtual environment settings affect the level of brain activation and whole-brain connectivity in people with cognitive impairment.
Existing studies have primarily used fMRI, EEG, and fNIRS to observe functional changes in brain regions associated with improved cognitive function. In the resting state, VR training positively affected attention-related brain activity in older adults with MCI: theta band power in subjects' parietal area and frontal area were significantly reduced, and the theta/beta ratio (TBR) was lowered. VR training also improved functional connectivity in brain regions related to visual function. In the task state, frontal area activation was significantly reduced in subjects after VR training, suggesting that the intervention improved neural efficiency. Some studies have shown that VR training is significantly better than traditional exercise or traditional combined training in improving cognitive function in MCI elderly. The activation of some brain regions in the task state and theta band power in the resting state parietal area was significantly lower in subjects performed VR training compared to the control group performed the traditional intervention. However, the traditional exercise group performed better in terms of delta/alpha ratio (DAR), TBR, and resting state alpha connectivity.
VR training is expected to become a supplementary method for cognitive improvement in elderly MCI patients. However, existing research still lacks a unified standard for defining the degree of VR immersion. For specific cognitive functions, the mechanisms by which factors such as the degree of immersion, training form and task content affect intervention outcomes still require further research. There are findings on neuroscience that mainly focus on changes in brain function in the resting state, with relatively insufficient findings on brain activity in the task state. The effects of VR training on brain structure and other neurophysiological activities in older adults with MCI are not yet clear. Future research should clarify the dose-effect relationship of VR intervention, focus on its long-term effects, and further explore the potential mechanisms of VR training to improve cognitive function in elderly MCI patients.

Key words: virtual reality, mild cognitive impairment, elderly, cognitive function, brain function