1. Introduction
ue to the nearly doubling of the elderly population, paying attention to this period’s issues and needs is a social necessity. In old age, various functions of the body, including balance, are affected. Balance describes the body’s dynamics to prevent falls and is influenced by power, reaction, and deep sense. Systems theory is one of the most prevalent and accepted theories of balance. Systems theory believes that maintaining balance Results from function between different nervous, muscular, and skeletal systems.
Non-invasive brain stimulation techniques such as tDCS are an excellent choice for changes in neural activity and neuroplasticity. Electrical stimulation of the brain can take place in different areas of the brain. Cerebellar tDCS is a non-invasive, simple, tolerable, safe, and harmless side effect. Zandvliet et al. (2018) showed a positive effect of tDCS on static balance in the elderly [14]. On the other hand, Steiner et al. (2016) [16] and Floel et al. (2012) concluded that tDCS has no significant effect on learning in the elderly [9].
Given that researchers have confirmed the effectiveness of tDCS on various aspects of life and various disorders and some studies on the effect of tDCS on balance; however, they have reached conflicting Results. This study aimed to investigate the impact of unilateral and bilateral electrical stimulation on balance in the elderly.
2. Methods & Materials
This study is quasi-experimental, performed using three groups with a pretest-posttest design and a control group. The statistical population of the study included all inactive male elderly in Ilam city. A total of 36 people were selected by convenience sampling method and divided into 3 groups of 12 people. In the unilateral electrical stimulation group, the Mean±SD age was 69.08±2.84 years, the Mean±SD weight was 67.66±9.59, and the Mean±SD height was 1.62±0.07. In the bilateral electrical stimulation group, the Mean±SD age was 68.91±2.57 years, the Mean±SD weight was 68.01±7.44, and the Mean±SD height was 1.61±0.06. And in the control group, the Mean±SD age was 69.16 ± 1.58 years, the Mean±SD weight 66.00±7.44, and the Mean±SD height was 1.61±0.05.
In the pretest stage, all participants underwent the Stork Static Balance Test. The participants were randomly divided into three groups. The intervention was held in 3 sessions every other day. In the unilateral transcranial electrical stimulation group, the anode electrode was placed at point O (International System of 10-20) in the cerebellar area, and the cathode electrode was placed at the top of the left ocular cavity (1FP). In the bilateral transcranial electrical stimulation group, the anode electrode was located at point O1, and the cathode electrode was located at point O2. The stimulation intensity used in this study was 2 mA at a time of 15 minutes per session. In the control group, as in the experimental group, the anode and cathode electrodes were placed at points O and 1FP, respectively, but the excitation current was cut off after 30 seconds. Immediately after the last training session, the posttest was performed, and once again, all participants took the Stork test.
3. Results
The One-Way Analysis of Variance (ANOVA) was used to compare the groups in the pretest and posttest stages (Table 1). 



Table 1 shows no significant difference between the static balance of the groups in the pretest stage (P<0.05), which indicates that the groups are equally distributed. And the level of significance in the posttest stage is significant (P<0.002).
The Bonferroni post hoc test Results showed a statistically significant difference between the unilateral electrical stimulation group and the control group (P=0.001) and the bilateral electrical stimulation group with the control group (P=0.005). Still, there is no significant difference between the unilateral electrical stimulation group and the bilateral electrical stimulation group (P=0.599). These Results indicate both groups of unilateral electrical stimulation and bilateral electrical stimulation are better than the control group, and there is no difference between the two groups of unilateral and bilateral electrical stimulation.
4. Conclusion
In explaining the Results of improving the balance of unilateral electrical stimulation and bilateral stimulation relative to the control group, electrical stimulation of the brain can cause neurodegeneration, which can alter functional connections in the human brain. It causes blood flow to the brain to be distributed in the stimulated region, where more blood flows and the hemoglobin increases in the area where the connection is strengthened. Therefore, it causes better performance than external stimuli, and the person’s balance increases following these interactions.
The effect of tDCS is known to modulate the motility of the primary motor cortex through glutamate receptors, GABA, brain-derived neurogenic factor (BDNF), and calcium-dependent mechanisms. On the other hand, it can cause arousal in the cerebellum. In other words, direct transcranial electrical stimulation can increase cerebellar stimulation and have a direct influence on improving function.
 In general, it can be stated that cerebellar tDCS unilaterally and bilaterally can improve balance in the elderly. Considering the importance of balance in the elderly, it is recommended to use this method. Among the limitations of the present study were the relatively small number of subjects and the use of the male gender alone, which is suggested to be considered in future research. It is also recommended that other balance tests such as Biodex and Equilibrium Tester be used.
Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Ethics Committee of Ilam University of Medical Sciences (Code: IR.MEDILAM.REC. 1397.154). All the procedures of the study were explained to participants, and all their questions were answered before they were asked to participate in the study.
Funding
This study is taken from the approved plan of Ilam University of Medical Sciences.
Authors' contributions
All authors equally contributed in preparing this article.
Conflicts of interest
The authors declared no conflict of interest


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