The Effect of Cerebellar tDCS on Static and Dynamic Balance of Inactive Elderly Men

Introduction

Since the slope of aging in Iran is like that of many countries around the world, it is argued that one quarter of Iranian population will be the elderly over the next 40 years, and paying attention to the issues and needs of this particular age group is highly crucial (Beyranvand et al., 2018).

As we age, changes occur in the function of the somatosensory, musculoskeletal, atrial, and visual systems as physiological systems involved in balance, and the elderly are exposed to serious injuries caused by imbalance, including falls, bone fractures in different areas and long-term disabilities. These factors can affect coordination and control of static and dynamic balance (Zampieri et al., 2016; Salminen et al., 2009).

One of the most important abilities that is important for human movements throughout life is the ability to maintain balance (Goodway et al., 2019). Balance is recognized as a basic motor skill and can play an important role in standing (static balance) or preventing people from falling (dynamic balance) (Krampe et al., 2014). For the elderly, maintaining balance is essential to remain independent and to reduce the risk of disease and death. However, the ability to maintain a person’s static and dynamic balance is a key predictor of falls and an indicator of gait performance (Shubert et al., 2006). Considering that loss of balance has been one of the main causes of falls among the elderly in previous studies, the issue of balance in this age group is of great interest to many researchers (Sirohi et al., 2017).

On the other hand, it has been found that active and inactive elderly people use different abilities to maintain balance. Active elderly people mostly use proprioceptive efficiency to maintain balance, while inactive elderly people mostly use visual sense when performing balance movements (Hajinia et al., 2013). This indicates that the factor of being active or inactive must be considered when evaluating a person’s balance.

Research has shown that old age is associated with changes in cognitive and motor functions, leading to disrupted daily activities (Miller et al., 2012). This process is accompanied by changes in the brain, resulting in structural, physiological and metabolic changes in the brain, some of which occur in response to this decreased function. To date, no global strategy has been identified to stop this process (Baruch et al., 2014).

One of the key factors for providing such strategies is achieving a better understanding of neuroplastic changes during aging. Therefore, noninvasive brain stimulation techniques such as tDCS are a suitable choice for assessment of changes in neural activity as well as neuroplasticity changes (Antal et al., 2014). Electrical brain stimulation can modify cortical excitability and activity, resulting in changes in behavioral and cognitive functions (Flöel, 2014).

tDCS is a method that involves the use of low voltage direct current (2 mA or less) through the positioning of electrodes on the skull surface. This method is used to alter the transmembrane potential to change the level of excitability. The efficacy of using the tDCS method has been confirmed in the improvement of a variety of issues such as depression, increased cognitive control, motor impairment in children and adolescents, improved inhibitory control in hyperactive children, cognitive function, and cognitive rehabilitation (Fregni et al., 2015). Research has shown that tDCS can affect different aspects of postural balance and control, including sensory input, integration of sensory signals (sensory reassignment), or selective motor outcomes (Craig & Doumas, 2017).

Zandvliet et al. (2018) examined the short-term effect of tDCS on static balance function in the elderly with chronic stroke as well as healthy controls. Ten healthy elderly and 15 stroke patients participated in this study. The results showed that 20 min of 1.5 mA stimulation improves static balance and there was no difference between the two groups. Hardwick and Celnik (2014) conducted a study to investigate the effect of electrical cerebellar stimulation on motor learning. Thirty-three individuals (Kingston, Canada) participated in the study, assigned into three groups; an older sham group (mean age of 56.3 ± 6.8 years), a younger sham group (mean age of 20.7 ± 2.1 years), and an older anodal group (mean age of 59.6 ± 8.1 years). The results showed that 15 min of electrical cerebellar stimulation had a significant effect on reducing error rates and improving adaptive motor learning of the chaining task. Kaminski et al. (2016) used tDCS in their study on 21 young subjects and concluded that tDCS leads to a better function with lower error rates. In their research, Marotta et al. (2022) investigated the effects of tDCS on balance and gait in patients with MS (aged 40.6 ± 14.4 years) and showed that tDCS may provide non-sustained improvements in gait and balance in MS patients. Fertonani et al. (2014) showed that in older adults, tDCS improved naming performance and decreased verbal reaction times only if it was applied during task execution.

On the other hand, Steiner et al. (2016) conducted a study to evaluate the effect of electrical cerebellar stimulation on balance and stature control. Thirty healthy young people with a mean age of 23 years participated in the study and were divided into three groups of 10. The balance task was performed by force plate. The results showed that electrical cerebellar stimulation had no effect on balance and stature control.

In the previous study, it has been shown that the balance between elderly men and women is different (Iverson & Koehle, 2013؛ Valipour Dehnou & Motamedi, 2018). In Iranian society, there are many cultural restrictions for women compared to men, and for this reason, it is very difficult to have access to women and persuade them to participate in the research process. Moreover, given the diverse effects of tDCS on different aspects of life and considering that studies on the effect of electrical stimulation on balance has shown conflicting results, and on the other hand, since motor and physical processes (such as balance) play a significant role in the life of the elderly, the present study was conducted to investigate the effect of electrical cerebellar stimulation on static and dynamic balance of inactive older adults men.

Methods

Results

The results of demographic characteristics showed that in the test group, the mean and standard deviation of age, weight and height were respectively 69.08 ± 2.84 years, 67.66 ± 9.59 kg, and 1.62 ± 0.07 m, while they were respectively 69.16 ± 1.58 years, 66.00 ± 7.44 kg, and 1.61 ± 0.05 m in the control group. These results show that there is no significant difference between the two groups. The results of BCSE showed that scores of both groups were close to each other and did not differ much (p > .05).

The results for the mean and standard deviation of static and dynamic balance in pretest and posttest phases are presented in Table 1.

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Table 1.

Results for the Mean and Standard Deviation of Static and Dynamic Balance in Pretest and Posttest Phases.

Variable	Group	Pretest mean ± SD	Posttest mean ± SD
Static balance	Test	5.12 ± 0.44	5.92 ± 0.69
	Control	5.31 ± 0.72	5.24 ± 0.81
Dynamic balance	Test	11.29 ± 1.07	10.69 ± 0.78
	Control	11.28 ± 0.98	11.64 ± 1.16

MANCOVA test was used to compare pretest and posttest of the two groups of test and control based on the variables of static and dynamic balance. The results are presented in Table 2. First, the presuppositions of covariance analysis test were checked. The Shapiro-Wilks test was used to evaluate the assumption of normality of the data, and it was found that the significance level is greater than 0.05, so the assumption of normality was accepted. Considering that the level of the assumption of homogeneity of the regression slopes was greater than p > .05, this assumption was also confirmed. The results of Lune’s test were also confirmed to check the assumption of homogeneity of variance due to the non-significance of F (p > .05).

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Table 2.

Results of MANCOVA Test Between Test and Control Groups Based on Variables of Static and Dynamic Balance.

Source	Dependent variable	Type III sum of squares	df	Mean square	F	Sig.	Partial Eta squared
Pretest of static balance	Posttest of static balance	2.837	1	2.837	5.836	.025	0.226
Pretest of dynamic balance	Posttest of dynamic balance	6.351	1	6.351	10.305	.004	0.340
Group	Posttest of static balance	3.750	1	3.750	7.714	.012	0.278
	Posttest of dynamic balance	4.091	1	4.091	6.638	.018	0.249

According to the results of MANCOVA test, there is a significant difference between the test and control groups in static balance (p = .12) and dynamic balance (p = .18). Bonferroni Post-hoc test was used to further investigate the interactive effects, the results of which are presented in Table 3.

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Table 3.

Bonferroni Post-hoc Test Results in Posttest Phase in the Test and Control Groups.

Dependent variable	(I) Group	(J) Group	Mean difference (I-J)	Sig.
Posttest of static balance	Test	Control	0.801	.012
Posttest of dynamic balance	Test	Control	0.837	.018

As can be seen in the table, the results show that there was a significant difference between the test and control groups in static balance (p = .12) and considering the desirable improvement in static balance, cerebellar tDCS had positive effects on static balance among the elderly and their function improved compared to the control group. There was also a significant difference in the dynamic balance between the two groups (p = .18). Considering the desirable improvement in dynamic balance, the test group performs better than the control group. Therefore, cerebellar tDCS has a positive effect on the dynamic balance of the elderly.

Discussion

Direct electrical brain stimulation is a non-invasive method in which weak electrical current flows through the scalp and causes changes in the cerebral cortex. The aim of this study was to investigate the effect of cerebellar tDCS on static and dynamic balance of inactive older adults. The results showed that cerebellar tDCS intervention had a positive effect on static and dynamic balance of inactive elderly men.

These results are consistent with the findings of Zandvliet et al. (2018) who concluded that tDCS affects static balance in stroke and healthy elderly, the findings of Kaminski et al. (2016), Marotta et al. (2022) and the findings of Fertonani et al. (2014).

One can state that the cerebellar tDCS may lead to more precise control of the central nervous system of a patient over the fluctuations caused by imbalance and reduce the risk of falls, and ultimately, lead to better control of balance and maintenance of one’s position and stature. There are signs of age-related changes in balance and posture that increase the risk of falls. The increase in age may impair vision. In addition, as the nervous system and vestibular system age and the person gets older, the muscle strength decreases. This is a limiting factor in daily activities that may have negative impacts on a person’s balance.

The cerebellar tDCS is a simple noninvasive, tolerable, safe, and complication-free method (Hans et al., 2014) that, with different physiological mechanisms during and after stimulation, can increase the effect of different trainings and exercises on motor performance, neurological rehabilitation and motor system improvement (Gomez Palacio Schjetnan et al., 2013).

Using the tDCS technique, which is a safe and accepted method for the neuroscience community and other researchers in the field of research and therapy, a direct and weak current (for the purpose of treatment or research) is transmitted through specific electrodes to certain cortical areas, which facilitates or inhibits the activity of that part of the brain (Brunoni et al., 2012). Once the tDCS site is correctly selected and the appropriate protocol is used, one can expect that the motor-evoked potential and locomotion in the area under the anodal electrode will be facilitated and cortical formation will be associated with improved motor function and this way, it has a direct impact on the function of the desired movement (Stagg & Nitsche, 2011). Since the aim of the research was to improve balance, the O point was stimulated based on the 10 to 20 electroencephalographic system. This area is near the posterior lobe, basal ganglia, substantia nigra, and cerebellum, all of which play a significant role in balance. Stimulation of this area may have a direct effect on the balance of the individual and provide an effective impact on the cerebral cortex and subcortical areas (Azarpaikan et al., 2014).

In explaining the findings regarding the improvements in the balance of the test group compared to the control group, it can be stated that electrical brain stimulation can change neuroplasticity, which may be related to changes in functional connectivity in the human brain (Takai et al., 2016). This causes the cerebral blood flow to circulate in the stimulated area, which increases blood flow in this area and hemoglobin is increased in the area where the connection is strengthened (Polanía et al., 2011). This leads to better function compared to external stimuli, and therefore the balance of the individual is reduced after these interactions. TDCS can affect the membrane potential of the glial cells and thus the balance of neurotransmitters. This change is similar to what is physiologically observed in astrocytes during activation of nerve cells (Ruohonen & Karhu, 2012).

On the other hand, the results of the present study are inconsistent with the findings of Steiner et al. (2016). They stated that cerebellar tDCS had no effect on balance among young people, but the present study showed that cerebellar tDCS had a positive effect on balance. The major difference between the present study and that of Steiner et al. (2016) is related to the subjects. It may be argued that the processes of keeping balance are easier in young people compared to older people because in older people, balance functions decrease over time. Therefore, processes that improve balance in individuals can have a greater impact on the elderly compared to young people.

Among the limitations of the current research, we can mention the relatively small number of subjects and the use of male gender alone, which is suggested to be observed in future studies. It is also suggested to use other tests related to balance, such as Biodex, balance meter, etc., which are performed with advanced tools and devices, and evaluate the effectiveness of this protocol. Furthermore, considering that the long-term effects of tDCS on balance were not investigated in this research, it is suggested that this issue be investigated in future research.

In summary, it can be concluded that cerebellar tDCS is capable of improving static and dynamic balance in inactive elderly men. It is therefore recommended to use this method to improve the static and dynamic balance of inactive elderly men.