The Effect of Short-Term Mindfulness Training on the Emotional State of College Students with Different Levels of Mindfulness: Evidence from Neurophysiological Signals

Objectives: The objective of this study was to explore the effects of short-term mindfulness training on the emotional state of individuals with different levels of mindfulness, especially from the perspective of autonomic neurophysiological mechanism. Methods: 52 college students were divided into higher or lower dispositional mindfulness groups. Then they underwent the mea-surement periods of baseline, short-term mindfulness training and recovery. During these periods, wrist-worn wearable devices were used for recording their autonomic nervous system activities, including heart rate (HR), galvanic skin response (GSR) and pulse rate variability (PRV). The Positive and Negative affect Scale (PANAS) and the State Anxiety Inventory (S-AI) were used before and after the experiment. Results: The results showed that in both groups, instead of positive emotion, negative emotions and state anxiety re-duced significantly after the training. In terms of physiological signals, in lower-dispositional group, the HR of the recovery period were significantly lower than that of the other two periods, and the PRV of the recovery period were significantly higher. In higher-dispositional group, the GSR of recovery period was significantly higher than that of the other two periods. Conclusions: The results suggest that short-term mindfulness training works mainly by reducing negative emotions rather than increasing positive ones. Our findings also provide neurophysiological evidence for a better emotional intervention effect of short-term mindfulness training on individuals with lower dispositional


Introduction
Mindfulness refers to individual's conscious, nonjudgmental awareness of the current internal or external experience (Kabat-Zinn, 2010). Studies have shown that mindfulness training can effectively relieve individual stress, improve symptoms such as anxiety and depression (Goldin & Gross, 2010), help improve individual life and work happiness (Liu, Xu, Wang, & Liu, 2013;Ye, Song, Wang, & Pang, 2019), and also has significant effects in improving emotional regulation (Arch & Craske, 2006). In previous empirical studies, researchers had arguments towards the effect of short-term mindfulness training (one-time training ranging from 3 minutes to 1 hour) on individual emotional valence. Erisman and Roemer (2010) found that after short-term mindfulness training, participants showed more positive emotions responding to positive emotional materials. In Valim's et al. (2019) experiment, he found that this effect only existed in short-term mindfulness based on positive emotion awareness. The training based on concentration has no effect. However, Lalot's et al. (2014) research found after short-term mindfulness training, participants' reports of positive emotions decreased. It can be seen that the impact of short-term mindfulness training on emotional valence needs to be further explored. In view of the fact that some previous studies on the effect of long-term mindfulness training on emotional valence mostly proved the reduction of negative emotions (Liu, Liang, Duan, & Li, 2008), this study will explore if short-term mindfulness training can effectively reduce individual's negative emotions similar to long-term mindfulness training.
At present, some studies have explored the neural mechanisms of how short-term mindfulness training affects emotional states, including brain mechanisms and peripheral neurophysiological mechanisms. Researches on the physiological mechanism of peripheral nervous system mainly involve the discussion of the physiological indicators such as heart rate (HR) and blood pressure (BP) (Howarth, Smith, Perkins, & Ussher, 2019), but their conclusions were quite different. Zeidan et al. (2010) explored the effects of short-term mindfulness training on emotions and cardiovascular variables. They found short-term meditation training improved mood and cardiovascular variables. After each meditation, participants' HR and BP were significantly reduced. Valim et al. (2019) investigated the impact of short-term mindfulness training in different types on emotional states, and measured the heart rate at the same time. The result showed no significant difference in heart rate under any condition. At present, the discussion of peripheral neural mechanisms on how mindfulness affects emotions is still mainly focused on continuous or intensive mindfulness training (Balconi, Fronda, & Crivelli, 2018;Howarth, Smith, Perkins, & Ussher,  It is worth noting that mindfulness can also be regarded as a trait of individuals, reflecting their tendency of focusing on the present moment and self-regulation (Weinstein, Brown, & Ryan, 2009). Individuals with a high level of mindfulness tend to adopt a more receptive and non-judgmental attitude towards their own experience, and more often use a decentralized perspective towards their thoughts and emotions (Shapiro, Carlson, Astin, & Freedman, 2006).
Therefore, compared with those in a lower level of mindfulness, individuals with higher level of mindfulness have more positive emotions, higher subjective well-being, life satisfaction and less negative emotions (Chang, Huang, & Lin, 2014;Goldin & Gross, 2010). They are also more adaptable while the environment changes (Siegling & Petrides, 2014). Based on this, we hypothesize: Individuals with different levels of mindfulness may be different in emotional regulation, which means compared with low-level mindfulness individuals, high-level mindfulness individuals have a weaker emotional regulation effect after short-term mindfulness training.
In a word, this study will explore the impact of short-term mindfulness training on emotional state of individuals with different levels of mindfulness, and try to provide evidence of peripheral neurophysiology for the mechanism of how short-term mindfulness training influences emotional regulation.

Participants
All participants were from a university in Nanjing. 52 students (43 females) aged from 18 -23 (Mean 19.54; SD 1.04) participated the study. All of them had no experience in meditation or mindfulness practice, and had no brain disease, cognitive impairment, or sought treatment for psychiatric problems. Each of them signed the informed consent before the experiment.

Measures
• Five Facet Mindfulness Questionnaire (FFMQ) FFMQ was used to measure the dispositional mindfulness of the participants.

Materials
In this study, a self-developed programme was used for short-term mindfulness training. The programme was based on the book Mindfulness: A Practical Guide to Finding Peace in a Frantic World by Mark Williams (2011). The training mainly includes two parts: mindfulness breathing and body scanning practice.
The training was verbally conducted by a director who had received professional and systematic training of mindfulness courses, and had certain experience of guiding mindfulness.

Procedure
Before the experiment began, all participants were asked to fill out the FFMQ.
Then they were divided into higher or lower dispositional mindfulness groups according to the scores. The study was carried out by group intervention. Both groups underwent three periods, which were baseline period (5 min), training period (20 min), and recovery period (5 min). During the baseline and recovery period, participants were asked to stay in the resting state. When in the training period, they received short-term mindfulness training under the guidance of the tutor. During the whole process, all participants wore the wristbands to record their neurophysiology signals. PANAS and S-AI were used before and after the experiment.

Data Analysis
The data were analyzed using SPSS 25.0. Group differences in pre-test scores of positive emotion, negative emotion and state anxiety as well as FFMQ scores were respectively checked with independent-samples t test. Repeated-measure ANOVAs were used to explore: 1) the changes of positive emotions, negative emotions and state anxiety before and after the experiment (within-group variable: pre-test, post-test; between-group variable: groups); 2) the difference of changes of HR, GSR and PRV in different periods between two groups (within-group variable: periods; between-group variable: groups

Group Differences before the Experiment
The result showed that the group difference in FFMQ scores was significant (t = 10.24, p < 0.001), which meant the validity of group classification. There were no significant group differences in pre-test scores of positive emotion (t = 0.334, p = 0.740), negative emotion (t = −0.046, p = 0.963) and state anxiety (t = −1.275, p = 0.208).
The interaction effect between period and group was not significant (F (2, 49) = 0.909, p = 0.396, 2 η p = 0.018). Pairwise comparison showed that, in the higher-dispositional mindfulness group, there were no significant differences In the lower-dispositional mindfulness group, there were significant differences between training and recovery period (p = 0.021), baseline and recovery period (p = 0.021), but no significant differences were found between baseline and training period (p = 0.989) (see Figure 2(a)).

Discussion
The aim of the present study was to investigate the effects of short-term mindfulness training on emotional state of college students with different levels of dispositional mindfulness. For changes of emotional state, the scale data showed that there was no significant difference between the pre-test and post-test of positive emotion in both groups, while the post-test scores of negative emotion and state anxiety were significantly lower than those of the pre-test. These results indicate that short-term mindfulness training can effectively reduce individuals' negative emotions, but does not significantly affect individuals' positive emotions. This is basically consistent with previous studies based on long-term mindfulness training (Erisman & Roemer, 2010;Liu et al., 2008), indicating that short-term mindfulness training may have a similar mechanism to long-term mindfulness training.
From the perspective of neurophysiology, our study also investigated the changes of HR, GSR and PRV of participants with higher or lower dispositional mindfulness. In terms of HR, the results showed that in the higher-dispositional mindfulness group, no significant difference was found among three periods.
However, in the lower-dispositional mindfulness group, HR during recovery period was significantly lower than that during baseline and training period, and there was no significant difference between the baseline and training period.
These results indicated that short-term mindfulness training can effectively reduce the HR of individuals with low trait mindfulness. It was shown in the previous studies that HR would significantly improve when individual negative emotions increased (Brosschot & Thayer, 2003), while the change of HR was not obvious when positive emotions increased (Hubert & Jone-Meyer, 1990). These results suggested that short-term mindfulness training may have a better effect on the negative emotions of lower-dispositional mindfulness individuals.
In terms of GSR, the results showed that in the higher-dispositional mindfulness group, the GSR during the recovery period was significantly higher than that during the other two periods. In the lower-dispositional mindfulness group, there was no significant difference among three periods. These results indicated that short-term mindfulness training can effectively improve the GSR of individuals with higher-dispositional mindfulness. Previous studies have shown that human sweat secretion is affected by emotional arousal. When emotional arousal increase, the GSR will increase, while when emotional arousal decrease, the GSR will also decrease (Khalfa et al., 2002). That is, changes in GSR can reflect the individual's ability of emotional arousal to some extent. In this study, only indi- For example, the neglect and indifference to emotional information can effectively weaken the emotion, and on the contrary, the emotional response will increase. Compared with individuals with lower-dispositional mindfulness, individuals with higher-dispositional mindfulness tend to have stronger ability to detect emotions, so they are more likely to improve the awareness and arousal of emotions in a short period of mindfulness training.
In terms of PRV, the results showed that there were no significant differences among three periods in the higher-dispositional mindfulness group. In the lower-dispositional mindfulness group, the PRV in the recovery period was significantly higher than that in the other two periods. These results indicated that

Conclusion
Short-term mindfulness training works mainly by reducing negative emotions rather than increasing positive emotions. It may promote emotional state by decreasing HR, and increasing GSR and PRV. In addition, short-term mindfulness training may have a better effect on regulating emotions for individuals with lower-dispositional mindfulness.