Introduction
Decreased HRV has been reported in various illnesses, including depression, psychotic disorders, and autism. For example, in autism, resting HRV is decreased, especially in relation to emotional control [
1], and in schizophrenia and bipolar disorder, HRV has also been associated with severity of psychiatric symptoms [
2].
Several studies have reported relationships between altered autonomic function and Internet addiction by examining heart rate variability (HRV) at rest or during a computer task [
3,
4,
5,
6,
7,
8,
9] (Supplementary Table).
Heart rate variability reflects the balance between parasympathetic and sympathetic activity at the sinoatrial node, and the HRV spectrum can be divided into very-low, low (LF: 0.04-0.15 Hz), and high (HF: 0.15-0.40Hz) frequency bands that reflect different autonomic inputs. The HF component is considered to most strongly reflect vagus-mediated parasympathetic input [
10]. However, the HF band is influenced by respiration and there is no broadly accepted method to remove this influence [
11]. Alternatively, the [
12]. LF band spectrum is thought to be mix of sympathetic and vagal activity, baroreflex activity. They highlight a link between cardiac sympathetic nerve activity and baroreflex sensitivity. However, traditional time and frequency domain measures fail to account for important properties related to multiscale organization and nonequilibrium dynamic. So the non-linear analysis based on entropy is recently investigated [
13,
14].
The HRV spectrum is computed directly from the variation in R-R (inter beat) intervals through statistical computation, which is sensitive to the length of the recording. Owing to the use of different acquisition and analysis procedures, it may be difficult to compare results across studies. In order to address this problem guidelines have been proposed [
15,
16].
Despite the methodological heterogeneity, such studies tend to show a weak relationship between HRV and Internet gaming addiction (Supplementary Table). Specific HRV indices may reflect the capacity of individuals to modulate cognitive activity, emotion, and behavior in response to changing environmental demands [
17]. According to the perspective of Porges [
18,
19] and Thayer [
20] HRV is a biomarker of top down regulation. Therefore, abnormalities in the HRV spectrum may predict deficits in cognitive, emotional, and (or) behavior control that predispose to Internet addiction.
Young people and students are considered more vulnerable to problematic Internet use [
21,
22].
While many studies have examined 24 hour HRV to evaluate cardiovascular neural regulation among health care workers [
23], shift workers [
24] and patients with coronary artery disease [
25], such measures have not been conducted in healthy young adults with problematic Internet uses. The HF component displays a circadian pattern with peak power between 11 PM and 5 AM [
26]. This circadian rhythm was altered in coronary artery disease patients [
25] and night-shift workers [
24]. Thus, long-term HRV analysis may be a more reliable tool for assessing autonomic dysfunction, as well as its relationship to disorders such as Internet addiction than, measurements during specific tasks [
27]. But, the short-term HRV analysis is easy to perform and convenient to control the confounding factors.
In this study, we evaluated the differences in the HRV spectrum over 24 h and during computer tasks in males with or without excessive Internet gaming (EIG) behaviors. In addition, we compared the HRV spectrum between young adults and high-school students to assess the potential differences in behavioral control with maturity.
Discussion
To the best of our knowledge, this is the first study to examine autonomic changes in young males with and without excessive Internet gaming behaviors using 24 h HRV monitoring. While there was no difference in the HRV band power change (min-max) between the EIG and non –EIG groups, we found a significant difference in the daily average of HF. On the other hand, there was no significant difference in HF during IGT or when the subject was playing games that he played every day.
The results of the previous reports on HF at rest showed that HF decreased when depression [
39] or Internet dependence were strong [
3,
4,
5,
6,
7,
8,
9], which was the opposite of the present results. The subjects in this study did not demonstrate the severity of Internet addiction observed in previous studies [
3,
4,
5,
6,
7,
8,
9]. The present study was conducted on healthy subjects classified by IAT, and the low level of severity was considered to be a reason for which no significant differences were found except for HF. HRV is related to frontal lobe function, and moderate game use is reported to have a positive effect on it [
40].
According to Tateno et al. [
41], an IAT cut- off point of 40 is not appropriate to evaluate Internet addiction, while 50 may be ideal.
In addition, the 24 hour measurement was insufficient, including sleep and various daily activities. Strictly speaking, it is necessary to conduct more detailed studies on the differences in the amount of exercise, sleep stage, etc., by using accelerometers and PSG together.
The clinical usefulness of Heart rate variability is not yet well understood, whether short-time or 24-hour measurements are better. For example, in myocardial infarction Lu et al. [
42] demonstrated that SDNN of a 5-min ECG recording could predict the mortality of patients with myocardial infarction, but was inferior to long- term HRV indices. In contrast, Bigger et al. [
43] compared the power spectrum of short ECG recordings with 24 h long-term HRV, and concluded that both HRV analyses were excellent predictors of mortality in patients with myocardial infarction.
There was a significant difference in the depressive state, anxiety, impulsivity, autistic tendency, and sleep problems between both groups; thus, at the early stage of excessive Internet gaming, psychometric testing appears superior to HRV monitoring for evaluating the psychological factors contributing to this aberrant behavior. Using multimodal biosignals such as EEG and galvanic skin response [
44], as well as other kinds of tests such as an individual minute test, which evaluates time perception, will improve the detection of Internet gaming addiction [
45]. In the past, gaming, social tasks and watching films have been used to evaluate heart rate variability reactivity (
Table 1), but there was not significant result compared to the baseline heart rate variability [
2].
Hong et al. [
7] also observed significant reductions in HF power during periods of high attention and during the last 5 min of the task. It is possible that the time course of the game may influence HRV. However, we did not find time course changes between both groups in terms of HF during the IGT.
When the overall results were classified by age, there were significant differences in the IGT scores and responses to IGT between the high-school students and the adults. In other words, the IGT scores were significantly higher in adults than in high-school students, and the responses to HF were greater in adults than in high school students. This is consistent with the authors of [
46], who found that adolescents have a poor decision-making process and lower IGT results. It is also consistent with the results found in [
47] according to which the better the IGT results, the more autonomic activity is activated. In Table 3, there was a significant difference in BMI between both groups, but Antelmi et al. [
48] found no significant difference in terms of HRV between the normal, overweight, and obese groups of men and women.
Therefore, it is reasonable to limit the time and content of Internet use for high school students who are in the process of maturing their decision-making process, as has been conventionally established.
According to a recent review, there is a small but significant relationship between HRV and top-down self- regulation, and this relationship is thought to be stronger in older individuals [
17]. The observed differences in terms of HRV in our study between age groups suggest such a relationship.
This study has several limitations. First, excessive Internet use was less severe than in previous studies, so relationships between HRV indices and EIG are still possible. Second, we did not monitor respiratory changes during game playing, and differences in respiratory response could influence the HF band of the HRV spectrum. However, a recent study found no significant group difference in respiration during a gaming task [
4]. Third, we did not consider specific details of the participants’ Internet use such as excessive social networking and online shopping, gambling, or pornography use.
In conclusion, the 24 hour average HF of the wearable sensor demonstrated a significant difference between the EIG and non -EIG groups. Contrary to previous results, however, the averaged HF was higher in the EIG group, which was more likely to be depressed and to have pre-Internet tendencies. This result was an evaluation of net-dependent tendencies in healthy subjects, and it is possible that a moderate use of the net may have resulted in functional improvement.
Younger participants also tended to exhibit a decreased HF response during the IGT, which may be related to weakness in top down self regulatory mechanisms compared to older individuals.
In this study, we performed long-time measurement for 24 hours and short-time loading for a few minutes, and found significant differences only in the long-time frequency analysis. In the future, in addition to the parameters to be compared in the analysis method, it is necessary to solve such problems as what kind of load is likely to cause differences in short time, and whether the long time measurement should be divided into resting and sleeping periods.