Adolescence is a transitional phase, moving from school age to adulthood, marked by manifold physiological and psychological bewilderments typically referred to as a turbulent period. During adolescence, the brain undergoes structural and functional changes, such as the pruning of unnecessary synapses, making it unstable [1]. The limbic system, which is responsible for emotions and motivation, develops before adolescence and becomes highly active during adolescence [2]. In contrast, the prefrontal cortex, which is responsible for cognitive control, develops more slowly, and its growth continues into early adulthood [3]. Consequently, adolescents often display characteristic emotional and behavioral patterns influenced by emotions and rewards rather than judgments based on values and goals, leading to difficulties in self-control [1,2].

Attention is generally a neurophysiological brain function that impacts behavior [4]. Attention is a brain function crucial for inducing information processing to select and classify necessary resources from various external stimuli [5,6]. The mental effort involved in selecting, maintaining, and switching attention during the process of focusing attention is an essential factor in adolescent learning and requires stringent self-control [5,7]. When adolescents are repeatedly trained to focus on new information attentively, choose behaviors accordingly, and combine this action with motivation, thereby receiving immediate rewards, the basal ganglia adapts this process to form a habit. The prefrontal cortex is activated to enable continuous self-control for sustained goal pursuit and to maintain the learned behavior [2].

Self-control in adolescents is an internal skill of decision-making that involves analyzing and integrating one’s emotions, cognition, and behaviors to select and adjust socially acceptable means toward achieving one’s desires. It is a developmental process of growing to maturity and important because it affects social adaptation, academic achievement, and emotional stability [8]. Adolescents engaging in negative behaviors and repeatedly failing to control their impulsivity because of the difficulty of self-control can lead to habitual behaviors, resulting in negative and problematic behavioral outcomes [8,9]. This situation underscores the importance of providing adolescents with practical nursing interventions designed to enhance their ability to focus attention and reinforce self-control.

The attention and self-control of high school students can reportedly be improved through brain training [8]. Although self-control brain training that considers the brain development of late adolescents is being conducted globally [3], South Korea primarily practices interventions centering on meditation, acceptance-commitment therapy, and cognitive-behavioral therapy to enhance attention and self-control [5,10]. However, research on brain training interventions for brain development is lacking. In particularly, the increase in sex hormones and brain development during adolescence can cause psychological imbalances, affecting behavior and leading to sex differences [1,3,11]. Previous studies have demonstrated that male adolescents have lower self-control scores [11] and higher impulsivity, engaging in more negative problem behaviors compared to females [12]. However, research focusing on male high school students is lacking. Moreover, even though changes in the brain’s neural network, such as the reduction of gray matter, occur after around age 12 between preadolescence and adolescence for males [1], research has been conducted mostly on elementary and middle school students and rarely on high school students. This lack of research on high school students is primarily because of their time constraints under the current education system centered around college entrance exams. This study aims to identify the effects of brain training on the attention and self-control of male high school students to bridge this research gap.

Biofeedback is a training method that focuses on an individual’s physiological responses and enables them to voluntarily control them to normalize abnormal biometric indicators displayed on a computer monitor. This approach allows for active regulation and maintenance of ideal psychological and physiological responses [13]. There are multiple types of biofeedback, including respiration, temperature, heart rate variability (HRV), blood pressure, electrodermal response (EDR), electrodermal potentials (EDP), surface electromyography (EMG), and neurofeedback. While other types of biofeedback focus on physiological responses, neurofeedback focuses on brainwave changes [14]. Neurofeedback, a brainwave change-focused biofeedback, is a brain function improvement program that can change brain activity states by controlling selective brainwaves through repetitive training [15,16]. This training can rectify abnormal brainwaves [9,15,17]; when applied to normal individuals, it can serve as brainwave control training to enhance cognitive functions [16]. This study conducted two-step biofeedback training based on the Reflection and Reflexion model [18] for self-control. This stepwise combined biofeedback training (SCBT) allows for repetitive learning focused first on physiological responses to attention and then on brainwaves. Moreover, it reconfigures the networking of the body and brain by providing real-time visual and auditory feedback on changes in the physiological responses and brainwaves, improving the ability to exercise self-control and sustain attention [19].

Previous nursing studies that have applied brain training have primarily focused on either attention or self-control among adolescents. These studies have observed changes in variables such as stress and creativity or have provided biofeedback training centering on physiological responses or neurofeedback training focused on brainwave changes as a single intervention [9,19]. However, nursing intervention studies that conduct biofeedback training, combining systematic and stepwise strategies to enhance attention and self-control abilities, are needed considering the brain development of high school students.

Hence, this study aims to provide male high school students with physiological response-focused biofeedback and brainwave change-focused biofeedback training in a stepwise combined manner based on the “Reflection and Reflexion” model [18] and to verify its effects on attention and self-control. This study seeks to provide academic evidence for the feasibility of using the SCBT as an independent nursing intervention considering adolescents’ brain development.

In this study, we conducted the SCBT to enhance the functioning of the prefrontal cortex in male high school students and verify its effect on improving attention and self-control based on a brain-cognitive neuroscience approach anchored in the Reflection and Reflexion model [18].

The attention enhancement training software program, used for physiological response-focused biofeedback training, is non-invasive and can measure physiological indicators through electrodermal conduction. Electrodermal conduction measurement is currently applied in various technological domains for relaxation and attention enhancement [2]. It is expected to be utilized as a biomarker for nursing interventions to improve attention and assess the level of attention in fields such as psychiatric nursing and community nursing.

There were significant changes observed not only in the experimental group but also in the comparison group which have got physiological response-focused biofeedback training, a direct comparison cannot be made because of the limited domestic research on attention-enhancement training software programs similar to this study applied to high school students. Nonetheless, a study conducted with middle school students [29] yielded similar results in improved attention. Notably, in contrast to a previous study with 36 sessions [29], our current study demonstrated a significant change in attention rate after only 10 sessions of training, which is presumably attributable to the physiological response-focused biofeedback training that was designed to improve the attention of midadolescents, aged 16~17, whose working memory is functioning at adult levels [1].

After the SCBT, the physiological attention span was statistically significant only in the experimental group. Although making a direct comparison is challenging because of a lack of previous research measuring attention span after providing the SCBT, similar to our study, the significant increase in self-control score observed exclusively in the experimental group can be explained by the mechanism of the C-system, based on the Reflection and Reflexion model [18]. During this training, the experimental group actively engaged the C-system to consciously acquire self-control strategies and maintain their physiological attention span [18]. This observation also aligns with previous findings indicating that self-control positively impacts the physiological attention span, representing the capacity to sustain attention [5,7].

Self-control showed a statistically significant difference in score changes only in the experimental group. While the control group’s total scores decreased, the experimental group exhibited a statistically significant increase. This statistically significant increase in self-control scores observed only in the experimental group could be attributed to their brainwave change-focused biofeedback training. The experimental group participated in brainwave change-focused biofeedback training based on operant training through repeated rewards [9,30], and the Reflection and Reflexion model [18]. Repetitive training, which performs similarity-based pattern-matching operations on incoming data for improving attention, stimulated and activated the brains of the experimental group’s participants, resulting in improved self-control [8,9,18,30]. Enhanced self-control induces effective changes, allowing adolescents to focus on goals that can provide greater rewards than the ineffective thoughts initially perceived in challenging situations [8]. The observed significant differences in the subscales of willpower, self-regulation, and motivation to change were exclusively found in the experimental group. These differences can be attributed to the SCBT. This combination enabled the experimental group to quantitatively adjust complex psychophysiological processes that are challenging to perceive and deliberately adjust for them to ponder on and apply new attention strategies [14,30]. Furthermore, the real-time visualization, hearing, and feeling of the changes in brainwave patterns during training boosted the experimental group’s confidence and self-efficacy, improving their ability to self-control themselves [19].

From a neuropsychological perspective, attention can be categorized into four distinct types: selective attention, which focuses only on the current experience; divided attention, which allocates attention to two or more different tasks simultaneously; sustained attention, which maintains attention over a specific time interval; and shifting attention, which redirects attention back to the original target or shifts focus between tasks [7]. In particular, self-control is essential for adjusting the capacity to sustain, select, and switch attention to maintain attention [5]. Considering the crucial role of self-control in maintaining unwavering attention, the significant improvements in physiological attention span and self-control observed exclusively in the experimental group of this study can be attributed to the efficient influence of the SCBT. This training method was more effective in prolonging attention span than single biofeedback training.

Finally, in this study, after participating in the SCBT, the experimental group showed an increase in the intensity of alpha and SMR waves and a decrease in high-beta waves. Comparing these changes directly to previous research that conducted the SCBT in the same brainwave range is challenging because of the lack of available studies. However, a previous study conducted with adolescents, in which brainwave change-focused biofeedback training was conducted to investigate changes in alpha, SMR, and beta waves, reported increases in this brainwave range after intervention [19]. Additionally, it is important to note that the beta wave results in this previous study were achieved through training that initially lowered high-beta waves and then raised mid-beta waves, which might explain the differences from the high-beta wave results observed in this study. The changes in SMR waves in the experimental group of our study are considered attributable to the result of operational conditioning [9] and the outcome of the deliberate, reflective system [18]. In the first phase of SCBT, which is physiological response-focused biofeedback training, participants habitually use their own attention methods to engage with the software training program. This reaction is the X-system. But this approach fails. This situation caused them stress, but they endeavored to discover the most effective ways to enhance their attention, thereby enabling them to concentrate on the training. Most of them increased their attention level when they relaxed. In the second phase of SCBT, which is brainwave change-focused biofeedback training, the software training program operated with increased difficulty due to the specifically set goals for changing brainwaves. However, they used a new strategy for maintaining attention that they acquired in the first phase. When they successfully implemented their new method, the program provided real-time visual feedback as a reward during the training process. Because reward sensitivity in the brain increases in midadolescence [1], they were able to control themselves to increase relaxation, reduce stress, and maintain attention through repetitive training. Consequently, through the repetitive brainwave change-focused biofeedback training, their brainwaves were changed. The C-system elucidates this [18]. Repeated training of the SCBT can enhance self-control and develop a new attention strategy in the form of an automatic pattern-matching response. This is a new X-system [18]. These changes reflect the repetitive efforts to modify brainwaves to maintain a state of attention and relaxation, driven by real-time visual feedback through training.

Furthermore, in this study, participants experienced relief from heightened alertness and tension from the alarm state [18] because of repeated brainwave change-focused biofeedback training, which likely led to the strengthening of the most stable alpha waves in a self-accepting state. Additionally, this study provided brainwave training to suppress hypervigilant high-beta waves, which reduced the intensity of high-beta waves. This reduction is assumed to be because of the more immediate responsiveness to instant rewards in adolescent brains compared with adult brains [1,6].

The gamified elements incorporated into the SCBT used in this study likely acted as effective learning strategies, inducing interest in new learning and enhancing attention regulation [6]. Furthermore, in a stepwise combined manner, the brainwave change-focused biofeedback training was applied to adjust brainwaves after strengthening cognitive abilities through physiological response-focused biofeedback training. The latter is known to enhance attention and cognitive discrimination [25], which contributed to drawing out the ability to change brainwaves more efficiently.

However, there are several limitations to generalizing the findings of this study. Since the study was conducted in two regions and three high schools through convenience sampling, it has limited generalizability. We adjusted the training schedule to minimize the impact of differences between schools and classes when selecting participants to improve generalizability. Future research may require random participant selection to address this limitation.

Moreover, recruiting is challenging in general high schools, which are influenced by university entrance exams, making it difficult to implement the entire ten session program because of concerns from schools and parents. To address this issue, training would be necessary to be during weekends, vacations, or extracurricular hours. In order to confirm the effectiveness of the SCBT in normal high school students, we excluded adolescents who were left-handed and students who had received psychiatric treatment or interventions. Therefore, we suggest that future research should include them. Although this study compared and analyzed three groups to examine the effects of SCBT, future research is recommended to further enhance the effectiveness of SCBT by adding a single intervention group focusing on brainwave biofeedback as a comparison group, enabling a complete four-group comparison. Finally, this study was conducted before the COVID-19 pandemic, and we propose conducting a follow-up study targeting high school students exposed to the changed educational environment caused by COVID-19. Our findings could provide a helpful foundation for comparing a follow-up study pre- and post-COVID-19.

Despite the aforementioned limitations, when considering the results of this study, the SCBT, aimed at fostering adolescent brain development and delivered as an independent nursing intervention, is significant in that it improved attention and demonstrated changes induced by self-control in high school students. In previous studies on attention [5,12] among adolescents, evaluations were mostly based on observations and self-report questionnaires completed by students, lacking objective assessments. In contrast, this study objectively evaluated attention using physiological indicators and objective assessments of brainwave- changes associated with self-control.

Furthermore, this study utilized brain-computer interface devices in the era of digital health to implement nursing assessments based on physiological responses and cognitive neuroscientific approaches. This pioneering attempt holds significance for nursing interventions not only in the field of community schools but also in clinical practice. In the United States, this intervention has been recognized as a powerful approach to enhance brain function and alleviate cognitive deficits in patient populations [30]. Also, the passage of the Nursing Act has heightened the need for professional and independent nursing interventions by nurses inside the community of South Korea. Thus, we hope that further research will continue to explore the application and adaptation of non-invasive, nonpharmacological interventions using the proposed stepwise training, combining physiological response-focused biofeedback and brainwave-focused biofeedback, not only in local community school settings but also in practical clinical nursing practice.

This study was conducted to develop the SCBT based on the Reflection and Reflexion model [18] as a stand-alone nursing intervention which was applied to male high school students to test its effects on attention and self-control in the study population. As a result, the nursing intervention training for attention improvement showed significant effects attributable to positive feedback of reward and reinforcement in the reflexive system (X-system), and self-control significantly enhanced in the reflective system (C-system) to foster value-based behaviors among adolescents. Therefore, the SCBT in this study is expected to serve as a stand-alone nursing intervention that will ultimately induce goal-oriented behaviors, allowing individuals to control and resolve their issues positively. Particularly noteworthy is the improvement in data objectivity achieved by comparing and analyzing physiological indicators and psychological variables together, complementing the limitations of self-report questionnaires.

Furthermore, to explore the potential spread and application of visual and auditory repetitive training among participants experienced with video-related media technology because of remote learning during the COVID-19 pandemic, conducting follow-up research with adolescents of varying age groups is recommended to assess age-dependent effects. We also recommend conducting follow-up research applying the proposed nursing intervention to address various cognitive and behavioral issues in adolescents or testing its effects in various areas.