Introduction
The Parkinson disease is the most prevalent progressive neurological disorder after Alzheimer disease, associated with a wide range of cognitive, psychological, and behavioral impairments. At present, there is no definitive cure for the disease, and patients generally do not respond significantly to medications and surgeries. Hence, increasing attention is being paid to multidisciplinary rehabilitation strategies, which are less invasive and yield more sustainable long-term effects. Among these, virtual reality (VR) has emerged as a promising rehabilitative tool in recent years. While VR is considered effective, few studies have specifically investigated its cognitive and behavioral benefits for patients with Parkinson disease. Accordingly, this study evaluates the effectiveness of VR-based balance training on the cognitive performance of elderly individuals with Parkinson disease and mild cognitive impairment.

Methods & Materials 
This semi-experimental study used a pretest/posttest design. The statistical population consisted of elderly individuals with Parkinson disease and mild cognitive impairment who attended a rehabilitation center in Tehran City, Iran. The participants were selected based on inclusion criteria, such as being in stages 1 to 4 of Parkinson disease and having a confirmed diagnosis of mild cognitive impairment by a geriatric specialist. A total of 30 patients were conveniently sampled and randomly assigned into two equal groups, namely an intervention group and a control group. The intervention group received routine rehabilitation along with VR-based balance training using a system developed at the Smart Neurorehabilitation Technologies Research Center (affiliated with Sharif University of Technology). 
This system included a monitor, sensor-equipped camera, and a stand. The camera detected patient movements and projected them into a virtual environment, with task difficulty customized to individual capabilities based on speed, quality, angle, and object distance. The program consisted of two weekly sessions for eight weeks (16 sessions total), each lasting 45 min. The control group received only standard rehabilitation care. Data collection tools included the Hoehn and Yahr scale (for staging Parkinson disease) and the Parkinson disease cognitive rating scale for assessing cognitive performance. Data analysis was conducted using the SPSS software, version 26, with paired and independent t tests at a significance level of 0.05.

Results 
Descriptive statistics were used to summarize demographic and intervention variables. The Shapiro-Wilk test and Levene test confirmed normal data distribution and variance homogeneity. Meanwhile, the Chi-square test showed no significant differences between the groups regarding gender, education level, age, height, weight, disease history, or stage, indicating group equivalence. Also, the paired t tests showed no significant pre-post differences in the control group, while significant improvement was observed in the intervention group. Independent t tests also revealed a significant difference in posttest cognitive scores between the groups, affirming the effectiveness of the intervention. 
The paired t test results for the Parkinson disease cognitive rating scale scores showed that in the control group, the pretest mean was 67.46 (standard deviation [SD]=2.06) and the posttest mean was 67.73 (SD=1.15), with a t value of 1.00 and a P value of 0.33, indicating no significant change. In the intervention group, the pretest mean was 68.46 (SD=2.38), and the posttest mean increased to 72.26 (SD=2.40), with a t value of -6.20 and a P value of 0.001, reflecting a significant improvement. The independent t test comparing posttest scores between groups showed that the control group had a mean of 67.73 (SD=1.15) and the intervention group had a mean of 72.26 (SD=2.40), with a t value of -5.43 and a P value of 0.001, indicating a significant difference between the groups. These results provide strong evidence that the VR-based balance training significantly enhanced cognitive performance in the intervention group.

Conclusion
The study demonstrated that 8 weeks of VR-based balance training led to cognitive improvement. These findings align with previous research supporting the positive role of VR in cognitive rehabilitation for Parkinson disease. The training appeared especially beneficial in the early stages of the disease. Further studies suggest that prolonged cognitive-motor VR training could lead to even greater cognitive gains. One possible mechanism behind the cognitive improvements is neural plasticity, the brain’s capacity to reorganize and form new neural pathways in response to training and stimulation. The exercises may slow cognitive decline and enhance executive functioning by activating healthy brain regions.

Ethical Considerations
Compliance with ethical guidelines
This study has received approval from the Ethics Committee of Islamic Azad University, Science and Research Branch, Tehran (Code: IR.IAU.FRB.REC.1402.55)

Funding
This study is part of Ali Mehraban’s master’s thesis. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

Authors' contributions
Conceptualization, methodology, software, validation, formal analysis, investigation, resources, data curation, writing–original draft preparation: Ali Mehraban; Writing–review & editing, visualization, supervision, project administration: Azadeh Sadat Zendehbad and Fereidoun Nowshiravan Rahatabad.

Conflicts of interest
The authors declared no conflict of interest.

Acknowledgments
The authors extend his sincere thanks to Dr. Zendehbad and Dr. RahatAbad for their guidance, and to all participants and staff at the Tabassom Clinic, especially Dr. Kazemi, for their support and collaboration.
 

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