Fear is an emotion closely linked to evolution as an adaptive response to environmental threats. When the fear responses are triggered excessively in non-fearful situations, they may develop fear-related disorders in individuals. Fear of heights is one of the most fundamental basic survival responses, often accompanied by physiological and behavioral changes (Liu et al., 2021). People may exhibit a mix of autonomic, behavioral, and cognitive self-preservation responses when they anticipate danger, including breathing faster, heart rate increases, freezing, and avoidance (Borkar and Fadok, 2021; Christianson, 2021). In some cases, irrational or excessive fear of heights can develop into acrophobia, which can significantly interfere with normal daily activities (Arroll et al., 2017). Acrophobia is estimated to affect around 3.1–6.4% of the general population (Lebeau et al., 2010). Additionally, visual height intolerance (vHI) is also a distressing susceptibility to height stimuli that affects 28% of the population, with about half of those who are susceptible reporting a negative impact on their quality of life (Huppert et al., 2013). From susceptibility to height intolerance to acrophobia, there exists a continuum of cognitive and physiological responses to height exposure (Brandt et al., 2015).

Many therapeutic techniques focus on reducing or eliminating of fear in both humans and animals. Pharmacological treatments, such as protein synthesis inhibitors, have been used in animal studies to alter learned fear, which may have long-term effects on the modulation of fear memories and defensive reactions (Nader et al., 2000; Mckenzie and Eichenbaum, 2011). Such interventions cannot be used safely in humans due to a number of serious side effects, including leukopenia, lipid abnormalities, sleepiness, and weight gain. Apart from pharmaceutical interventions, non-pharmacological strategies have the potential to facilitate to eliminate fear responses as well. Device-based methods, such as transcranial direct-current stimulation, transcranial magnetic stimulation, and transcutaneous vagus nerve stimulation, have been found to improve extinction and alleviate fear responses (Burger et al., 2016; Pennington and Fanselow, 2018; Clarke et al., 2020). However, it is important to note that the effectiveness of device-based techniques in reducing fear may vary. Some research has shown that the application of a-tDCS did not significantly reduce feelings of fear in patients or animals (Manteghi et al., 2017; Wout et al., 2017). These conflicting findings could be attributed to differences in brain targets and stimulation frequencies used in the studies.

Cognitive behavioral therapy (CBT) is a commonly used non-pharmacological strategy that aims to modify maladaptive emotional responses by changing an individual’s thoughts, behaviors, or both (Kaczkurkin and Foa, 2015). Cognitive and behavioral flexibility allow us to adapt to different situations, shifting strategies as needed to meet changing environmental demands and also play a central role in evidence-based practice approaches for the treatment of fear and anxiety disorders (Powers et al., 2017). For example, attentional bias toward threat stimuli was found to improve in a study involving a single-session CBT for panic disorder (Kappelmann et al., 2020). About half of the variance in symptom change were explained by early reductions in attentional bias toward threat, which were found to predict better symptomatic improvement at a 1-month follow-up (Reinecke et al., 2013). Exposure therapy is one of the widely used CBT treatment method that has been found to be highly effective for specific phobias. Meta-analytical studies have shown that exposure therapy is more effective compared to no treatment, placebo treatment, and non-exposure-based active therapy conditions (Wolitzky-Taylor et al., 2008). These intervention strategies provide promising approaches for managing and reducing fear and anxiety. However, previous studies have focused on behavioral and the neural correlates of cognitive emotion regulation, and have not focused on investigating emotion regulatory strategies that directly involve the body, despite their effectiveness in clinical populations (Minewiser, 2017; Church et al., 2022; Menevşe and Yayla, 2023). Aside from the cognitive, behavioral and motivational concomitants, emotions have long been recognized as full-body events. Emotional Freedom Techniques (EFT) is a psychophysiological intervention that includes cognitive and somatic elements and it adds the novel ingredient of acupressure. Instead of using needles, practitioners stimulate acupuncture points by tapping on them with their fingertips (Stapleton et al., 2023). Extensive research on Clinical EFT has demonstrated its effectiveness in reducing symptoms of post-traumatic stress disorder (Clond, 2016; Sebastian and Nelms, 2017; Feinstein, 2022). Moreover, body tapping is also well suited for self-application in non-clinical settings because of its simplicity, such as sports performance, public speaking and university exams (Baker and Siegel, 2010; Church, 2010; Rahmi, 2013). The inclusion of body-based techniques in research and practice can provide a more comprehensive understanding and approach to emotion regulation.

Previous studies have primarily focused on emotion regulatory strategies, neglecting the necessary intervention duration. It may be due to the fact that reductions in fear and avoidance are easy to observe and measure, but they occur slowly. In many instances, clinical or experimental, the cognitive shifts are slow to develop, changing over weeks rather than minutes (Rachman, 2015). Several studies have found that EFT can lead to significant reductions in anxiety, even in a single-session application (Chatwin et al., 2016; Jasubhai and Mukundan, 2018; Dincer and Inangil, 2021). The visualization of body tapping as a means of emotional regulation has been shown to effectively alter immediate neural and behavioral responses to emotional stimulation by single-session (Wittfoth et al., 2020). Similarly, tapping acupoints has been shown to increase amygdala activation and decrease hippocampus activation in individuals with flight phobia (Wittfoth et al., 2022). It is suggested that EFT can be capable of regulating fear in the daily lives of healthy individuals, even with minimal time investment.

However, tapping acupuncture points with fingertips has limitations that restrict people’s actions and is unsuitable for situations that require physical manipulation. Because manual stimulation of acupuncture points can produce endogenous opioids, increase the production of neurotransmitters and regulate cortisol (Menevşe and Yayla, 2023). Cortisol is the main stress hormone and modulates the autonomic nervous system, reduces heart rate, pain, and anxiety through these neurochemical changes (Lane, 2009; Napadow et al., 2009). Therefore, acupuncture may have the capacity to modulate emotional reactions. But the acupuncture is an invasive intervention technology, it has certain safety risks when used in some scenarios with poor sanitary conditions. One study showed that transcutaneous electrical acupoint stimulation (TEAS) can reduce post-operative stress response and improve heart rate variability, with effects no different from traditional acupuncture (Zhou et al., 2020). TEAS is an emerging therapeutic approach that combines the effects of transcutaneous electrical nerve stimulation (TENS) with acupuncture point stimulation (Szmit et al., 2023). Some studies have shown that acupuncture at PC6 can relieve and control palpitations, and its effect is closely related to autonomic nervous function (Liu et al., 2020; Ye et al., 2023). Based on these findings, we hypothesize that applying TEAS at Neiguan (PC6) can produce a similar emotion regulation effect. This approach utilizes a portable electrical stimulation device that can automatically stimulate acupoints (Air Force Medical University, Xi’an, China) to implement TEAS. This would enable a more convenient and comprehensive intervention, potentially applicable in multiple dangerous situations such as aerial work, driving or flying.

In this study, we investigated whether TEAS at PC6 could effectively reduce fear exposed to the virtual height stimulation by single-session. The results demonstrated that the intervention had significant effects on reducing fear, as evidenced by changes in physiological responses and behavioral and cognitive parameters. These findings provide evidence supporting the use of TEAS as a means of emotion regulation in response to negative emotional scenes in healthy participants.

The significant differences observed in verbally reported fear scores and PANAS fear scores between the intervention group and the control group suggest that intervention was effective. These findings align with previous research highlighting the anxiolytic effects of acupuncture (Smith et al., 2018; Fu et al., 2022). It has been well-established that fear and anxiety often coexist and share common physiological and cognitive processes (Etkin and Wager, 2007; Mcteague et al., 2010). Anxiety is characterized by apprehension, worry, and anticipation of future threats, and it can intensify the fear response and prolong emotional arousal. Individuals with anxiety disorders exhibit heightened fear responses and are more prone to developing phobias (Lissek et al., 2009, 2010). Additionally, our findings are consistent with previous research on cognitive-behavioral interventions for specific phobias (Wang et al., 2022). The intervention of TEAS likely affected maladaptive thoughts and beliefs associated with the stimuli, resulting in a reduction in fear and anxiety.

HRV reflects the adaptability and flexibility of the autonomic nervous system and is particularly associated with cardiac vagal tone, which is relevant for various psychophysiological phenomena, including self-regulation mechanisms linked to cognitive, affective, social, and health (Thayer et al., 2009; Mccraty and Shaffer, 2015). Previous research has examined the association between HRV and emotion regulation strategies, suggesting that changes in HRV can reflect the effects of emotional interventions to some extent (Geisler et al., 2013; Zaccaro et al., 2018). In the present study, the control group exhibited lower SDNN values compared to the intervention group, indicating that the intervention had a positive impact on HRV, as reflected by higher SDNN values in the intervention group. Research has shown that SDNN is associated with various physiological and psychological processes. Higher SDNN values have been linked to better cardiovascular health, improved stress resilience, and enhanced emotion regulation (Thayer and Lane, 2009; Laborde et al., 2017). Conversely, lower SDNN values have been associated with increased risk for cardiovascular diseases, poor mental health, and worse anxiety (Quintana and Heathers, 2014; Larsson et al., 2023). Therefore, the intervention may indicate a potential improvement in cardiovascular function and stress regulation. Some researchers suggest using HRV indices that clearly reflect identified physiological systems with a theoretical underpinning, such as RMSSD, peak-valley, and HF (Laborde et al., 2017). The HF band reflects parasympathetic activity and lower HF power is correlated with stress, panic, anxiety, or worry (Shaffer and Ginsberg, 2017). In this study, the intervention group exhibited higher lnHF compared to the control group, indicating that TEAS may have an effect on the parasympathetic activity of the participants. As research suggests, higher vagal tone is associated with better executive cognitive performance and improved emotional and health regulation (Thayer and Lane, 2009; Thayer et al., 2012). Higher vagal tone has also been linked to better emotion regulation abilities, including the ability to downregulate negative emotions and upregulate positive emotions (Kok et al., 2013). These findings support our result that TEAS can increase vagal tone and enhance emotion regulation abilities. A wider distribution with greater variability will result in a larger TINN value, indicating a more irregular heart rate pattern. Conversely, a narrower distribution with less variability will yield a more regular heart rate pattern. The significant difference observed in TINN between the two groups may indicate that the intervention can lead to a more regular heart rate pattern.

Non-linear analyses may be more appropriate and accurate for HRV analysis, as the autonomic nervous system exhibits complex and irregular fluctuations (Piskorski, 2005). SD1 is supposed to be more sensitive to quick and high frequent changes whereas SD2 is viewed as an indicator of long-term changes. The ratio of SD1/SD2, which measures the unpredictability of the RR time series, is used to assess autonomic balance. In our study, the intervention group had significantly higher SD2 compared to the control group, while the SD1/SD2 ratio was significantly lower. According to our result, the vagus and sympathetic balance was affected by the intervention, improving cardiac autonomic modulation and reducing stress state. One study demonstrated that SD2 decreased significantly during a stress session compared to a control session, which was attributed to university examinations (Melillo et al., 2011). This finding supports the conclusion that higher SD2 may represent a lower state of stress.

Behavioral parameters, such as eye movement parameters and task performance, were also assessed in this study. Eye movements and spatial attention are closely interconnected systems that often shift together in many circumstances (Hodgson, 2019). The intervention group exhibited higher left eye openness compared to the control group, indicating a potential improvement in attentional focus and cognitive processing. One possible explanation for the increased left eye openness in the intervention group is that participants needed to intermittently look at the VR displaying buttons while using the VR controller with their right hand for task button interaction. As a result, the left eye observed toward the VR controller generated a greater offset, leading to higher eye openness. People direct their eyes toward objects of interest with the aim of acquiring visual information. However, processing this information is constrained by capacity, requiring task-driven and salience-driven attentional mechanisms to select a few among the many available objects (Souto and Kerzel, 2021). Thus, our observations suggest that attention, driven by TEAS, is biased toward cognitive tasks rather than fear stimuli. Although there were no significant differences in saccade amplitude and pupil diameter, the intervention group exhibited faster RT in the nine-light task and greater MD compared to the control group. The RT is influenced by the stages of cognitive processing involved in a task. Cognitive processing involves several stages, including perception, attention, memory encoding, decision-making, and response execution (Mittelstädt and Miller, 2020). Each stage requires a certain amount of time, and the cumulative time taken by these stages determines the RT. Emotion regulation has been found to have an impact on cognitive performance. Research suggests that individuals who are better able to regulate their emotions tend to exhibit improved cognitive functioning, such as enhanced attention, memory, and task performance (Gross, 2015). The smaller RT indicated that the intervention had a positive effect on reducing participants’ fear responses and improving cognitive performance. Furthermore, the greater movement distance observed in the intervention group suggests a reduction in avoidance behaviors and an improvement in coordination and execution of actions. Fear motivates different types of defensive behaviors and these defensive behaviors may in turn reduce, preserve, or amplify fear responding (Pittig et al., 2020). Based on the subjective scores and movement performance, we believe that participants in the intervention group experienced less fear, which led to lower avoidance behavior, manifested by an increase in walking distance.

Our study findings indicate that a single-session of TEAS at PC6 effectively reduces fear of heights. The results demonstrate that the intervention group had lower fear scores compared to the control group. Additionally, supporting evidence is derived from improvements in heart rate variability, increased left eye openness, faster reaction times, and greater movement distance observed in the intervention group. These findings suggest that TEAS has the potential to reduce fear, enhance cardiovascular function and emotion regulation, improve attentional focus and cognitive processing, and decrease avoidance behaviors. PC6 may be a suitable acupoint for regulating emotions in response to negative stimuli when using TEAS. However, further research is needed to fully understand the neural mechanisms underlying these effects.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving humans were approved by the Ethics Committee of the Air Force Medical University. The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.

LC: Writing – review & editing, Writing – original draft, Visualization, Validation, Software, Project administration, Methodology, Investigation, Formal analysis, Data curation, Conceptualization. XY: Writing – review & editing, Writing – original draft, Methodology. MH: Writing – review & editing, Writing – original draft, Data curation. JS: Writing – review & editing, Writing – original draft, Methodology. HL: Writing – review & editing, Writing – original draft, Methodology. TZ: Writing – review & editing, Writing – original draft, Software, Formal analysis. WD: Writing – review & editing, Writing – original draft, Software, Formal analysis. CT: Writing – review & editing, Writing – original draft, Methodology, Formal analysis. KX: Writing – review & editing, Writing – original draft, Methodology. JM: Writing – review & editing, Writing – original draft, Validation, Formal analysis. WH: Writing – review & editing, Writing – original draft, Conceptualization. JW: Writing – review & editing, Writing – original draft, Conceptualization. SC: Writing – review & editing, Writing – original draft, Conceptualization.