 disorders (ASD), which often contributes to learning difficulties and caregiver burden. The present study aims to compare the effect of a traditional Chinese Chan-based mind-body exercise, Nei Yang Gong, with that of the conventional Progressive Muscle Relaxation (PMR) technique in enhancing the self-control of children with ASD. Forty-six age- and IQ-matched ASD children were randomly assigned to receive group training in Nei Yang Gong (experimental group) or PMR (control group) twice per week for four weeks. The participants’ self-control was measured by three neuropsychological tests and parental rating on standardized questionnaires, and the underlying neural mechanism was assessed by the participants’ brain EEG activity during an inhibitory-control task before and after intervention. The results show that the experimental group demonstrated significantly greater improvement in self-control than the control group, which concurs with the parental reports of reduced autistic symptoms and increased control of temper and behaviors. In addition, the experimental group showed enhanced EEG activity in the anterior cingulate cortex, a region that mediates self-control, whereas the PMR group did not. The present findings support the potential application of Chinese Chan-based mind-body exercises as a form of neuropsychological rehabilitation for patients with self-control problems. Chinese Clinical Trial Registry; Registration No.: ChiCTR-TRC-12002561; URL: www.chictr.org.


Introduction
Executive dysfunction, which refers to difficulties in working memory, attention, planning, response inhibition, mental flexibility, and/or self-monitoring, is a typical cognitive deficit associated with autism spectrum disorders (ASD). Of these executive dysfunctions, response disinhibition and mental inflexibility are relatively more common in individuals with ASD [1][2][3]. It has also been suggested that executive dysfunctions accounts for typical autistic features, such as uncontrollable behavioral and emotional reactions, repetitive behaviors, strong need for sameness, restricted interests, and inappropriate social communication and interaction.
As there is not effective pharmacological intervention for enhancing the executive control of emotions and behaviors in individuals with ASD, the majority of the interventions are primarily behavioral [4][5]. Despite the reported effectiveness of some of the behavioral interventions in reducing behavioral or emotional disturbances, the intervention programs tend to be very intensive and time consuming [6][7]. For instance, although applied behavioral analysis was found to be effective in reducing various autistic symptoms, it requires intensive training for at least 20 hours per week for at least two years [7]. Furthermore, such positive outcomes are less prominent for children with limited mental ability or more severe autistic symptoms, who are not able to follow the rules and requirements of the training [8]. In view of the limitations of the conventional interventions, some researchers have been exploring various alternative methods, such as massage [9][10][11], acupuncture [12][13], music therapy [14][15][16], and diet/ nutrition [17][18][19]. Although some preliminary data supports the positive effects of these novel interventions, the treatment efficacies remain largely inconclusive [20]. Our research team has been studying the effects of a traditional Chinese Shaolin medical concept (called Chanyi) in reducing some of the executive dysfunctions in individuals with ASD for the past years [21][22][23][24]. The present study further examines one component of this intervention approach, i.e., the mind-body exercise, as a possible intervention to improve the self-control of children with ASD.
According to the National Center for Complementary and Alternative Medicine (NCCAM) established by the US government, a mind-body intervention is defined as any intervention which ''focuses on the interactions among the brain, mind, body and behavior, with the intent to use the mind to affect physical functioning and promote health''. The fundamental assumption of these interventions is that because the mind and the body are inter-connected, individuals have the internal ability to change their own thoughts and behaviors to enhance their mental and physical health. Mind-body interventions have long been used in China to improve both mental and physical health, and are now becoming increasingly popular in Western countries. Moreover, a range of scientific studies have examined the therapeutic effects of mind-body interventions on depression [25][26], anxiety [27], insomnia [28], chronic pain [29], and cardiovascular problems [30].
Although the existing studies have found encouraging empirical evidence for the treatment efficacy of mind-body interventions, the majority of the studies have examined adult or elderly populations. As a result, the effects and applicability of mind-body interventions on the pediatric population are relatively less understood. A few studies have explored the effects of relaxation training and mindbody interventions on the psychological and cognitive functions of children, and the results have so far been positive [31][32][33][34][35][36][37][38]. It should be noted that many of the mind-body techniques, such as meditation and Tai Chi, requires either a high degree of mental control or involves slow movements that might not be easily mastered by children with particular neurodevelopmental disorders. Nevertheless, the emerging positive outcomes of certain forms of mind-body training for normally developed children have provided insights into their potential effects on children with ASD.
The present study investigated the efficacy of the mind-body exercise, Nei Yang Gong, which is one component of a newly developed mind-body intervention. The intervention, which is based upon a Chinese Chan tradition named Chanwuyi (i.e., Zen, martial arts and healing) from the Sanhuangzhai monastery [39], is also known as the Dejian Mind-Body Intervention (DMBI), as named after the Grand Master of Chanwuyi -Shi Dejian (a Shaolin monk). Recent empirical studies on this intervention have shown that it has positive effects in improving physical health, mood and cognitive function in community-dwelling adults [40], children with autistic/Asperger's disorder [22][23][24], and individuals with brain damage [41] and depression [25][26]. While the previous studies examined the effects of the holistic approach of Chanyi, which includes psychoeducation, mind-body exercises and diet modification, the present study examined the effect of a single component of the model, the mind-body exercises, as a possible intervention for children with ASD.
Somewhat like Tai Chi, Nei Yang Gong involves sets of slow movements that emphasize smooth, gentle, and calm movements. The basic principles and practices of Nei Yang Gong have been elaborated in two published books [39,42] and on the website of a charity foundation (www.chanwuyi.org). The practice of Nei Yang Gong has two primary functions. First, it aims to foster selfawareness and mental self-control to help restore a calm and relaxed state. Second, it helps to reduce stress, increase flexibility of the limbs, and improve the circulation of Qi and blood. For example, the ''shoulder relaxation'' movement helps to relax the neck and the shoulders while improving self-control and selfawareness. It should be noted that Nei Yang Gong has been developed on the basis of the Chan medical model, which emphasizes the maintenance of a natural and relaxed attitude to achieve smooth circulation of Qi and blood. In this way, Nei Yang Gong differs from some of the other mind-body techniques, such as mindfulness and meditation, which require a high degree of conscious mental awareness and self-control. Given its required ''natural'' attitude, it is anticipated that Nei Yang Gong will be easily mastered by and feasibly applied to children with ASD. Our hundreds of clinical cases of children with neurodevelopmental disorders reveal that even children with moderate mental retardation are able to learn and benefit from Nei Yang Gong.
Our previous randomized controlled study revealed the possible neural mechanism underlying the therapeutic effect of Nei Yang Gong [43]. It was found that regular practice of Nei Yang Gong was able to foster a simultaneously relaxed and attentive brain state, as reflected in increased electroencephalographic (EEG) alpha asymmetry and intra-and inter-hemispheric EEG theta coherence indices. In contrast, this altered brain activity was not found among the participants of the comparison group, who practiced Progressive Muscle Relaxation (PMR). As relaxation and attentiveness are both significant factors for improving performance, Nei Yang Gong can be regarded as both a cognitive enhancement method and a relaxation exercise. Therefore, it is anticipated that the children who practice Nei Yang Gong (i.e., the experimental group) will show greater improvement in self-control (as measured by standardized neuropsychological tests) and greater reduction in related behavioral and social problems (as measured by parental reports on daily behaviors and social communication) than children who practice PMR (i.e., the control group). Derived from the work of Jacobson [44], PMR is a conventional and wellestablished behavioral treatment technique. It was selected for the comparison group because of the repeated empirical support for the effectiveness of PMR in alleviating anxiety, physiological arousal, and behavioral disturbances [45][46][47]. Furthermore, given the concreteness and simplicity of PMR, it can be applied to children with ASD at a younger age and with a lower functioning level. Scientific evidence supports the applicability and effectiveness of PMR in reducing aggression, increasing self-control and inducing relaxation in children as young as age 6 [48,49] and in children with learning disabilities [50,51]. Moreover, a few studies have reported that PMR alone or as a component of Cognitive Behavioral Therapy has positive effects in reducing anxiety and disruptive behavior of individuals with ASD [52][53][54].
The present study also compared the neural activity patterns of the two groups as measured by EEG assessment during an inhibitory control task (i.e., a Go/No-Go task) to explore the possible underlying neurological mechanism relating to