بررسی تأثیر تحریک الکتریکی مستقیم مغز (tDCS) آندی بر انعطاف‌پذیری شناختی و تصمیم‌گیری اجتماعی در بازیکنان ماهر، نیمه‌ماهر و مبتدی فوتبال

Background and Purpose
At high levels of sports activities, especially in team sports, different teams aim to enhance the cognitive capacities of their players. It is expected that strengthening cognitive functions will contribute to better emotional regulation, ultimately leading to improved player performance. One of the key cognitive functions that positively influences sports performance is cognitive flexibility (1). Cognitive flexibility is one of the most important components of executive functions (EFs), and neurological studies have shown that EF capacity is closely linked to the prefrontal cortex of the brain (2). Additionally, research in sports psychology suggests that successful performance in athletes largely depends on their ability to make quick decisions and respond to both cognitive and physical demands simultaneously (3). Despite
 the importance of cognitive functions in sports performance, there is relatively few studies examining the cognitive capabilities of individuals with varying levels of expertise (skilled, semi-skilled, and amateur). The results of existing studies suggest that different levels of expertise can have distinct effects on cognitive functions, which in turn influence overall sports performance. It has been found that individuals with varying levels of skill differ not only in the amount and type of knowledge and information they possess but also in the strategies they use to predict, make decisions, and process information. Some researchers have demonstrated that skilled athletes tend to make better decisions than their less-skilled counterparts. For instance, studies using real-world models to investigate decision-making in soccer have shown that skilled soccer players make more accurate decisions compared to amateur players (3).
In recent years, neuroscience researchers have developed various experimental methods to improve cognitive functions. One such effective method is transcranial direct current stimulation (tDCS), which has been shown to have a significant impact on cognitive and behavioral functions (4), including cognitive flexibility (5). Considering that deficits in cognitive flexibility and social decision-making can negatively impact various dimensions of sports activities—including success motivation, efficiency, and overall performance—it is crucial to explore interventions that target cognitive and behavioral components, such as tDCS. However, few studies have investigated the effects of tDCS on these cognitive and behavioral factors in athletes. So far, only a limited number of studies have examined the effects of tDCS on cognitive and behavioral components in athletes with varying levels of expertise. The aim of the present study was to determine the effectiveness of tDCS on cognitive flexibility and social decision-making in skilled, semi-skilled, and amateur football players. The results of this research are expected to have practical implications for sports psychologists and professional coaches. If cognitive processes can be enhanced using tDCS, it may lead to improvements in executive functions and decision-making speed, ultimately helping to create more efficient and professional teams.
Materials and Methods
The study was semi-experimental research with two groups: an experimental tDCS group and a sham tDCS group, along with pre-test and post-test measurements. The statistical population consisted of male football players from Kurdistan province, from which 60 football players (Mage = 24.27) at skilled, semi-skilled, and amateur levels were selected using a convenience sampling method. These participants were then randomly assigned to either the experimental or sham tDCS groups, with 30 participants in each group. Each group included 10 skilled players, 10 semi-skilled players, and 10 amateur players. The experimental group received three sessions of anodal stimulation direct current stimulation (tDCS), each session lasting 20 minutes with a current intensity of 2 mA. The sham group received three sessions of sham stimulation. To collect data, the Wisconsin Card Sorting Test (WCST) was used to assess cognitive flexibility, and the Ultimatum Game (UG) was employed to measure social decision-making. The data were analyzed using univariate analysis of covariance (ANCOVA) with SPSS-22 software.
 
Results
The results demonstrated that tDCS led to a significant improvement in cognitive flexibility and social decision-making in the experimental group of football players, as compared to the sham group. Furthermore, the findings revealed that tDCS had a significant positive effect on enhancing social decision-making across all levels of expertise—skilled, semi-skilled, and amateur—among the football players in the experimental group when compared to the sham group.Table 1. Results of ANCOVA concerning the effect of tDCS on the cognitive flexibility and social decision making of soccer players in the experimental and sham groups
 
As shown in Table 1, there was a statistically significant difference between the two groups in terms of cognitive flexibility (F=36.65, p=0.001, η2 = 0.391) and social decision-making (F=36.65, p=0.001, η2 = 0.554). Bonferroni's post hoc test was conducted to identify which group (skilled, semi-skilled, or amateur) showed a significant difference. The results indicated that tDCS significantly improved cognitive flexibility in skilled and semi-skilled football players in the experimental group compared to the sham group (P<0.001). However, tDCS did not have a significant effect on the cognitive flexibility of amateur football players (P=0.422). Therefore, it can be concluded that electrical stimulation of the brain increased the cognitive flexibility in skilled and semi-skilled soccer players in the experimental group compared to the sham group, but it did not have a significant effect on the cognitive flexibility of amateur soccer players. The results of the Bonferroni test also showed that brain electrical stimulation significantly improved social decision-making in football players across all experimental groups (skilled, semi-skilled, and amateur athletes) compared to the sham group.
 
Conclusion
The results of the present study demonstrated that anodal stimulation of the frontal cortex increased the cognitive flexibility scores of skilled and semi-skilled football players in the experimental group compared to the sham group. Therefore, it can be concluded that practice, experience, and varying levels of skill play an undeniable role in the development of this cognitive ability. This finding is consistent with previous studies (5) that explored the effectiveness of brain electrical stimulation on cognitive flexibility and social decision-making, confirming the superior cognitive flexibility of skilled individuals in these abilities. A neurological explanation of the results of the present study can be that the observed effects of anodic stimulation, by depolarizing the neuron, cause a change in the resting state of the neuron and increase the excitability of the targeted area. It is possible that the cortical networks involved in response selection are more strongly affected by tDCS than those responsible for other cognitive functions, as these networks are specifically engaged in tasks related to decision-making and flexibility. The effect of tDCS in the targeted area depends on the polarity of the electrode (anodal or cathodal) during the stimulation and the specific brain area being stimulated. Therefore, anodal tDCS induces an excitatory effect, which may increase levels of glutamate (an amino acid associated with cognition), thereby enhancing cognitive flexibility, memory recognition, stimulus-response learning, and social decision-making (6).
The results of the present study have practical implications for sports psychologists and football coaches in improving the cognitive and behavioral functions of football players through tDCS. However, the findings should be interpreted within the context of several limitations. The sample size of the study was small, and replication studies with larger sample sizes are needed. Future research should focus on larger sample sizes, diverse contexts, and different populations. Additionally, a self-report method was used to collect the data, which is susceptible to various biases.
Funding
This study received no funding from public, commercial, or nonprofit organizations.
Authors’ Contributions
Conceptualization, Review and Research: Erfan Izadpanah, Mehdi Zemestani,  Drafting the manuscript: Mehdi Zemestani, Mohammad Maleki; Search and data collection: Erfan Izadpanah, Mehdi Zemestani; Revision and edition of the manuscript: Mehdi Zemestani, Mohammad Maleki
Conflicts of Interest
The authors declared no conflict of interest.