Long-Term Inquiry Meditation Reduces EEG Spectral Dynamics in Self-Schema Processing

Junling Gao¹, Hang Kin Leung¹, Bonnie Wai Yan Wu¹, Thuan-Quoc Thach², Jenny Hung³, Chunqi Chang⁴, and Hin Hung Sik¹*

¹Centre of Buddhist Studies, The University of Hong Kong, Hong Kong

²Department of Psychiatry, The University of Hong Kong, Hong Kong

³Division of Humanities, The Hong Kong University of Science and Technology, Hong Kong

⁴School of Biomedical Engineering, Shenzhen University, Shenzhen, China

Correspondence and requests for materials should be addressed to HHS, hinhung@hku.hk

Compliance with Ethical Standards

This study had received ethical approval from the Human Research Ethics Committee for Non-Clinical Faculties at The University of Hong Kong. Informed consent was obtained from all individual participants who were included in the study.

Author Contributions

JG designed and executed the study, interpreted the data, wrote the manuscript. HKL designed and executed the study, analyzed and interpreted the data, collaborated in manuscript writing. BWYW worked on recruitment and manuscript writing. TQT worked on the manuscript writing and revisions. JH worked on manuscript revisions. CC worked on data analysis. HHS collaborated on the study direction, recruitment, and manuscript revisions.

Acknowledgements

This study is supported by the Li Ka Shing Foundation.

 

Abstract

Objective

Intuitive inquiry meditation is a unique form of Buddhist Chan practice that actively and intuitively utilizes the cognitive functions of doubt to explore the concept of self. This event-related potential (ERP) study aimed to investigate the neural correlates for long-term intuitive inquiry meditation induced flexibility in self-schema processing, highlighting the role of doubt and belief processes in this exploration.

Methods

Twenty experienced- and eighteen beginner- intuitive inquiry meditators were recruited for this ERP study. The investigation involved the use of doubt and belief processes as they interact with  concepts of self and Buddha. A 128-channel electroencephalogram (EEG) system was used to collect the EEG data. The ERP data were processed and analysed using EEGLAB.

Results

It showed a double dissociation between beginners and experienced meditators in concepts of self and Buddha: intuitive inquiry meditation reduced the brain activity of beginners when they viewed the Buddha picture but not of themselves. However, for the experienced meditators, intuitive inquiry meditation reduced brain activity when they viewed images of themselves but not when viewing the Buddha image. Further event-related perturbation spectrum analysis revealed that monks had a more dynamic brain spectrum mainly at the theta wave range, indicating that monks engaged more dynamic cognitive resources than the less experienced participants.

Conclusion

Intuitive inquiry meditation could help beginning meditators to detach from concepts of the Buddha but not the self. However, for the long-term meditators, it is the opposite.  ERSP analysis shows that only long-term meditators have significant dynamic brain activities during intuitive inquiry meditation, which might enable these practitioners to become spontaneously detached from the concept of self. These findings shed light on the neural mechanism for long-term intuitive inquiry meditation regard to doubt process and its effect on self-schema processing.

 

Keywords:  Event Related Potential (ERP); Inquiry meditation (Zen, Chan); Self schema; Doubt; Belief; EEG spectral dynamics

Introduction

Meditation is increasingly recognized for its potential to reduce stress, regulate emotion, and promote mental clarity in contemporary society, where individuals often grapple with cognitive dissonance and uncertainty. Nowadays, individuals have fewer struggles from physiological challenges such as hunger and intensive physical labour but are frequently in situations that would induce mental stress, ambiguity, uncertainty, and disinformation. This is especially true in the present time, where current events and reality continue to challenge past expectations and believes instigating doubts and cognitive dissonance. Fortunately, the prefrontal lobe has lately evolved in the human brain to help cope with contradictions and feelings of scepticism, enabling us to make decisions meticulously (Aram et al., 2019; Semendeferi et al., 1997). From a cognitive perspective, doubt and belief are two essential components of human cognition. We have beliefs and schemas, which are formed from our experience to make swift decisions. At the same time, we need the doubt processing to continuously update past beliefs so they can more precisely reflect with reality. The doubting process, instead of dogmatic attachment/belief, is essential for critical thinking and development of an insightful mind that is the highlight of human intelligence. In this sense, the doubt process is as vital as belief for maintaining cognitive balance.

Attachment/belief appears in the infancy stage for both humans’ and animals’ development. It helps individuals to learn from their parents, thus improving their chances of survival. Belief is a broadly used concept and is empowered by intrinsic comprehension (Asp, Manzel, et al., 2012; Asp, Ramchandran, et al., 2012; Gilbert, 1993). Broadly speaking, a variety of mental representations, including knowledge, rules, opinions, and ideas, can be regarded as beliefs (Asp et al., 2013). These beliefs or cognitive representations can be retrieved and used as schemas in the brain, similar to tools in a warehouse, to facilitate our understanding and processing of concurrent information, as suggested by traditional theories on cognitive representation. Thus, belief is an autonomic state that facilitates understanding and responses to a continuous flow of new information. These automatic processes can lead to a swift automatic response, if not blocked by the counterbalancing processes of doubt and dismissal.

According to false tagging theory (Asp, Manzel, et al., 2012), belief is a primary, inevitable, and easy-to-follow cognitive process intertwined with comprehension. It is sustained by representations in the postrolandic cortex and is used for further cognitive manipulation and execution. Unfortunately, this process, commonly taken advantage of by scam phone calls, affects those that are most vulnerable and particularly senior citizen (Cohen, 2006).  Previous studies have found that doubt and disbelief are mediated by the prefrontal lobe, which may deteriorate with old age (Asp, Ramchandran, et al., 2012). In contrast to belief, doubt is a more retroactive process that checks and renounces potentially false information, which could cause a person to be subjected to misunderstandings, fraud and deception.

Thus, when compared with belief, doubt, disbelief and critical analysis is a more effortful process that could result in instability and confrontation. However, with the overwhelming amount of propaganda and advertisement in today world, doubt and analytical thinking could be important to a person healthy living because it would help a person to probe into the reality of the situation, away from dangerous beliefs and erroneous dogmatic assumptions.

            The doubting process plays an essential role in critical thinking, and it helps us to detach from dogmatic routines and assumptions, which prevent us from being creative. Creativity requires divergent thinking and sometimes breaking the routine schematic way of thinking and working. In contrast, the dogmatic need for structure impedes creative performance following schema-inconsistent information (Goclowska et al., 2014). There are several ways to train doubt and critical-thinking processes (Hertzog et al., 2008; Vartanian et al., 2013). Interestingly, intuitive inquiry meditation, a form of Chinese Buddhist practice, utilizes the doubting process to explore fundamental questions, encouraging practitioners to engage their full cognitive resources in this inquiry, ‘inquiring the beginning of the word’. In this approach, practitioners need to find a fundamental issue and question it continuously. The practitioner has to use the full scale of his attention or cognitive resources to fully inquire about the fundamental question he chose, and he needs to keep inquiring and doubting while ignoring anything else unrelated to the subject question. To break away from the restriction of dogmatic schema, intuitive inquiry meditation emphasizes the flexibility of the mind by observing the idle mind while contemplating the ever-changing mind and indeed the impermanence of reality (Yu, 1979; Lachs, 2012).

Among various kinds of meditations, intuitive inquiry meditation is rather unique. Practitioners of intuitive inquiry meditation are encouraged to examine and doubt all concepts and ideations without using conceptual analysis, but rather directly and intuitively approach the object of meditation with doubt and inquiry. Even concepts of the Buddha and self should be inquire, doubted and let go of before real enlightenment could be achieved. Intuitive inquiry meditators are not only guided to inquire and doubt the object of meditation, for example, the Buddha, inquiry and doubt should also be directed toward the one who is meditating, the self.  Chan masters often point out that one who has a small amount of doubt would leads to a low level of enlightenment, while a large amount of doubt would lead to a high level of enlightenment (CBETA, 2000; Singyun, 2006).

From a neuroscientific perspective, belief and doubt are two fundamental cognitive forces that shape our thoughts and subsequent behaviours. During the developmental stage of a baby, belief is formed earlier than doubt. This is true not only in the development of humans but also in animals for the purpose of survival. Doubt only appears in a much later stage of human brain maturity, and the prefrontal cortex plays an important role in the development of the doubt process (Asp, Manzel, et al., 2012). According to false tagging theory, doubt is an important process that helps the individual prevent the interference of false or unnecessary information during the decision-making process or while concentrating on an ongoing task (Asp, Manzel, et al., 2012).

In the current study, we analysed the most popular form of Chinese Chan (Zen) meditation practice, Can-Hua-Tou, ‘Who is chanting the name of the Buddha?’. This is a priming question to assist the meditator to develop a doubting and inquisitive mind toward the practice of repetitive religious chanting of the name of Amitabha Buddha, a most popular religious practice in the Mahayana Buddhist traditions. Our previous study investigated into the effect of religious chanting of practitioners who believed strongly in Amitabha Buddha. The ERP study showed that religious chanting could ameliorate the negative response to fearful events, probably by forming a positive schema during repetitive religious chanting. In contrast, repetitive chanting of the name of Santa Claus did not have a similar effect, although the participants also had a happy and familiar feeling associated with Santa Claus. The difference could be due to the fact that these practitioners had little belief in Santa Claus (Gao et al., 2019).

Further study revealed that religious chanting may reduce the eigenvector centrality of the posterior cingulate cortex (PCC), a region known for self-referential-related processing ( Gao et al., 2019). It is suggested that the neural mechanism of religious chanting may be attributed to concepts of self and belief. Indeed, some religious practices, such as those in the Pure-land sect of Mahayana Buddhism, emphasize the importance of belief. According to the pure land sect, having faith and belief in Amitabha Buddha is a prerequisite to the practice of religious chanting, and it is the practitioner, ‘the self’, that would be reborn in the pure land.

Intuitive inquiry meditation, on the other hand, making use of the popularity of pure land Buddhism, directed the practitioner to directly inquire into the identity of who is chanting the name of the Buddha. If it is the practitioner, ‘self’, who is chanting the name of Buddha, the priming question will direct the meditator to enquiry into’ who am I’, ‘what is self’, etc.. Basically, the meditator needs to develop meta-awareness to doubt and investigate into who is it that is chanting the Buddha’s name and who/what is the one that is conscious of all that that is happening.  At one point, the practitioner and the one who is doubting becomes the target object of inquiry during deep reflexive meditation. Other meditation methods such as those in Tibetan Buddhism (Mahamudra) also have inquiry process (Dahl et al., 2015), but intuitive inquiry meditation solely requires the meditator to intuitively engage in a process of inquiry and doubting without using conceptual analysis. A long-term intuitive inquiry meditation practitioner may thus train his capacity to concentrate on intuitive inquiry, that is, pondering without conceptual analysis. Intuitive inquiry meditation also helps the practitioner to cultivate a flexible and detached mental state while remaining cautious and doubtful toward what is perceived and conceived thereafter. These assumptions have widely been affirmed while no neuroscientific study has ever been launch to clarify it.

Our study focuses on the popular Chinese Chan (Zen) meditation practice, Can-Hua-Tou, 'Who is chanting the name of the Buddha?'. This question primes the meditator to develop a doubting and inquisitive mind, essential for the practice of repetitive religious chanting, a widespread religious practice in Mahayana Buddhist traditions. We will explore how this practice affects both belief and doubt processes, and its potential influence on brain regions related to self-processing. Moreover, as intuitive inquiry meditation promotes cognitive flexibility, we aim to investigate whether experienced intuitive inquiry meditators exhibit more dynamic brain activity due to their long-term training. This investigation will contribute to our understanding of the impacts of meditation on the neural underpinnings of human cognition.

Using ERP which can measure the dynamic brain activities, this study aimed to investigate how intuitive inquiry meditation would doubt and deconstruct the concept of self, and influence the meditator’s brain regions that are related to self-processing. The concept of self is to the interest of Buddhism and clinical psychology as well. We would investigate both doubt and belief processes, two counterbalancing but fundamental functions of human cognition. In addition, as intuitive inquiry meditation training engage the flexibility of the mind, another aim of this study is to investigate whether experienced intuitive inquiry meditators would have a more dynamic brain activity as a result of their long-term training.

 

Materials and Methods

The experiment was approved by the University ethics committee. Following our pilot study, 20 monks with advanced inquiry meditation experience and 18 layman Buddhists as beginners of the practice, all of whom were males, were recruited for this study. The monks were 48 (SD = 13) years old in average, while the laymen were 47 (SD = 11) years old in average. The monks all had inquiry meditation experience, mainly from the Chinese Chan tradition, for 5-28 years. Inquiry meditation is also called ‘Can-Hua-Tou’ where the practitioner needs to thoroughly and deeply enquires into the true identity of “Who is chanting the name of Buddha”. This form of meditation typically requires years and decades of pondering before eventual enlightenment is achieved. The participants in the layman control group had experiences in inquiry meditation, but all at the beginner level. Participants with mental or neurological diseases were not recruited in this study.

Event-related potentials (ERPs) were evaluated to delineate the potential neural correlates between the meditators’ reaction to the concepts of “self” and “Buddha”; this approach was taken because the concepts of ‘self’ and “Buddha” both have religious significant, but should have different neurological implications as one involve the identity of self as oppose to the Buddha which would represent an external object. This experiment was conducted with a 2 x 2 (within) x 2 (between) factorial design: two meditation conditions (inquiry vs. normal), two types of viewing pictures (Buddha vs. Self), and two groups of participants (monk vs. layman control). The two meditation conditions included an inquiry meditation condition and a normal control condition. A priming phase of “Who is chanting the name of Buddha” (念佛是誰in Traditional Chinese) was used to elicit an inquisitive meditative state in the inquiry meditation condition; whereas “Jia Yi Bing Ding” (甲乙丙丁 in Traditional Chinese) is a commonly used sequence, similar to the meaning of 1, 2, 3, 4 in Arabic but in Chinese characters, was used in the normal condition. Thus, the four Chinese characters were comparable to two conditions. Two types of pictures were shown after the priming, a picture of Buddha and a picture of the “self”, that is, the picture of the particular meditator himself, which was taken before the experiment and transformed by software (PhotoLab^TM) to ensure that the resolution and figuration of the two types of pictures were comparable.

The experiment had a block design to follow the real-world situation during intuitive inquiry meditation, and that the participant would not shift quickly from an inquiry meditation state back to the normal mental state in seconds. Given the limited time of an ERP experiment, a unique paradigm was designed, using a prime to imprint the inquiry/Chan state over other information processing. Each block lasted 150 seconds and contained 30 trials, each of the four unique scenarios were made up of two blocks, resulting in the randomized presentation of 8 blocks. In each trial, first, the priming phase was presented for 1.7-2.3 seconds, then an image of the participant or Buddha was presented for 2.1 seconds, and then a fixation ‘+’ would be presented for 0.9 seconds with jitter. The main aim was to continuously remind the participant to be in a state of inquiry meditation while watching and pondering the concepts of the self or Buddha. The participants performed a shorter practice run before starting the experiment. The ERP experiment lasted around 24 minutes with rest in between blocks.

The experiment took place in a quiet room of a temple for the monks and in a similar location for some of the laymen who were attending an intuitive inquiry meditation retreat. The rest of the laymen participated in the experiment in a quiet room of an EEG laboratory at the university. Datasets of 3 monks could not be used due to operational issues at the temple. The same equipment was used for both groups. E-prime (Psychology Software Tools, Inc. USA) software was used on a Windows PC for stimulus presentation. The participants were seated approximately 50 cm away from the monitor and had a full view of the images without much eye movement. EEG data were acquired using a 128-channel EGI system, and the impedance of electrodes was mostly kept under 30 kΩ, as instructed by the manufacturer. The EEG collection sampling rate was set at 1000 Hz, and the reference was set at the Cz location of the 10-20 system.

The EEG data were processed and analysed using EEGLAB based on the MATLAB platform. Data were pre-processed before analysis. The raw EEG data were converted into a format that could be read by EEGLAB, resampled from 1000 Hz to 250 Hz and filtered by a passband of 1-30 Hz. Data were cleaned manually, removing muscle artefacts and line noise. Channels with consistent artefacts were reconstructed using spherical interpolation. Further data cleaning was performed using independent component (IC) analysis. The ICs representing eye movement, muscle movement, and bad channel artefacts were discarded before data reconstruction using the remaining ICs. Finally, EEG epochs that were time-locked to picture stimulus onset (-300 ms to 900 ms) were extracted and averaged to obtain the ERP data, then average reference would be applied to each dataset. The effects of inquiry meditation on ERPs were obtained by subtracting the normal condition ERP signals from the inquiry condition ERP signals. Independent two-sample t-tests were used to determine the difference between groups.

The time-frequency analysis of the ERP data was performed based on event-related spectral perturbation (ERSP) and intertrial coherence (ITC). EEGLAB calculates the ERSP by computing the power spectrum in each ERP trial and then averages them across trials. This was done over a sliding latency window of 256 ms in each trial following gain mode (Delorme et al., 2004). To visualize a wider range of variation, log-transformation of these measurements was computed (Grandchamp et al., 2011).

ITC is a frequency-domain measure of the degree of synchronization of neural responses to a set of experimental events, with 0 indicating no synchronization and 1 indicating perfect synchronization. ITC is phase-locked, and a particular latency and frequency are specified for the ITC calculation (TallonBaudry et al., 1996). We used a 1-cycle wavelet to perform computation at a lower frequency. Repeated-measure analysis of variance (ANOVA) with false discovery rate (FDR) correction was applied to determine significant differences between groups and conditions. This analysis would be done after significant ERP results were obtained in those landmark channels of the 10-20 system.

Results

The ERP results demonstrated a differentiation between the meditation conditions, types of the image viewed, and the differentiation was mainly in the early stage of the time window (140-220 ms and 220-400 ms). These time windows were chosen based on our ERP study on priming effect of compassion and wisdom meditation (Gao et al., 2022; Sik et al., 2021). Stimulus onset time 140-220 ms is the stage of P100/N170 ERP for early visual information processing, while 220-400 ms is referred to as the P300 component that commonly used in ERP studies for earlier stage of information processing (Bridwell et al., 2018; Maurage et al., 2007). ERP analysis was made by comparing the effect of inquiry meditation while viewing images of the Buddha and the self, for both the layman control group and the experienced monk group. The layman group generally had a more negative trend in ERP line at channel Fz (medial frontal site). The two groups had different neural responses to the two types of images - participants in the layman control group had a more reduced brain response to Buddha’s image, while participants in the experienced monk group had a more reduced neural response to their own image (see figure 1, supplementary sFigure1 and sFigure2). The significance of the channel-based difference was made on the comparison of average amplitude of different time windows.

Interestingly, figure 2 demonstrates that intuitive inquiry meditation had a differential effect according to the inquiry target: while intuitive inquiry meditation by the experienced monks had effect on the target of self image (Normal: M = 1.22 uV, SD = 1.31 uV; Inquiry: M = 0.41 uV, SD = 1.06 uV; t(16) = -2.88, p = .011; the frontal channel Fz, see 4^th row 2^nd column of figure 2) , the layman control group’s inquiry meditation had effect only on the target of Buddha image (Normal: M = -1.63 uV, SD = 1.10 uV; Inquiry: M = -1.07 uV, SD = 0.81 uV; t(17) = 3.12, p = .0063; the frontal channel Fz, see 1^st row 3^rd column of figure 2). Also the effect of inquiry meditation appeared in an earlier stage (140-220 ms) in experienced group than in the layman control group (220-400 ms). (See figure 1 and 2).

Figure 1. ERP waveforms of two meditation conditions (inquiry vs. normal) for the two picture types (Buddha vs. self) in the two groups (experienced monks vs. layman control) at channel Fz. Thicker solid lines represent the control group.

 

Figure 2. Within group comparisons for the two different conditions. There was a clear double dissociation between the two groups - among the inquiry vs. normal conditions and two types of pictures viewed (self vs. Buddha). The power difference is represented by colours, red represent positive and blue represent negative. Dots illustrate channels with significant differences (p < 0.05), and darker dots indicate smaller p-values.

There was a clear double dissociation between the two groups. Participants in the layman control group showed a higher amplitude neural response (220-400 ms) to the Buddha image in the inquiry condition than in the normal condition (see the first row in figure 2). In comparison, the experienced monk group showed a greater response to self-image at 140-220 ms. However, monks also had the biggest reduced neural response to their own images in the inquiry condition when compared to the normal condition while viewing a self-image (140-220 ms, last rows of figure 2). These differences were still significant when compared across groups.

Difference between responses to images of self and Buddha

            There was a substantial difference when participants in both groups viewed their own images when compared to the image of Buddha in the normal control condition. The difference was most obvious in the P100/N170 component (see figure 3). There were similarities between the groups at this stage. There was also a difference in the P300 component for participants in both groups when viewing images of self and Buddha, though the direction was opposite in the two groups. For participants in the experienced monk group, the images of ‘self’ induced a larger P300 amplitude than the Buddha image (see the first row in figure 3) under normal condition of no meditation, whereas, for participants in the layman control group, the Buddha image induced a larger P170 and P300 amplitude than their own image around the Pz location (140-220 ms, see the second row in figure 3). The channel Pz is located at the medial parietal lobe. These differences mostly remained in the evaluation of participants in the layman control group under the inquiry meditation condition (see the second row in figure 4). However, these differences mostly disappeared among the experienced monk group, which could imply that the experienced monks might have viewed the concept of self and Buddha with equanimity and/or non-differentiation during inquiry meditation (see the first row in figure 4).

In the right fronto-temporal region, viewing the image of Buddha induced a different brain activity of the N170 component in the layman control group compared to the experienced monk group. The difference remains significant when participants viewed images of themselves. These differences are independent of the inquiry or normal condition, and they may reflect a general difference in the meditators respond to the viewing of concept of the Buddha and the self.

 

Figure 3. Group comparison of the picture viewing differences under normal condition. There are differences of pictures-viewing of self vs. Buddha in both groups. The power difference is represented by colours. Dots illustrate channels with significant differences (p < 0.05), and darker dots indicate smaller p-values.

Figure 4. Group comparison of the picture-viewing differences under inquiry condition. At 140-220 ms, there are significant differences in viewing pictures of Buddha vs. self for the control group (2nd row); however, no such difference found among monks (1st row); this difference still exist when further comparing between groups (3rd row). The power difference is represented by colours. Dots illustrate channels with significant differences (p < 0.05), and darker dots indicate smaller p-values.

ERSP and ITC analysis of the Fz channel

The difference between groups and conditions was greater in the frontal area than in other areas. In fact, participants demonstrated a nearly opposite ERP direction in the early-stage response to these images depending on the group to which they belonged. We further calculated the ERSP for normal conditions.

Figure 5. ERSP analysis at channel Fz shows difference between conditions while viewing picture of self. Significant differences were found around 200 ms in the Monk group (p < 0.05, fdr corrected).

ERSP demonstrated a consistent result: only the participants in the experienced monk group had greater ERSP when viewing their own images and a greater reduction during intuitive inquiry meditation. The difference was most significant at a time window of 180-220 ms, and at theta wave (4-8Hz).

Figure 6. ITC analysis at channel Fz shows difference between conditions while viewing picture of self. Significant differences were found around 200 ms in the Monk group (p < 0.05, fdr corrected).

ITC demonstrated that the monks had a greater ITC when viewing their own image; in other words, the monks had a greater reduction in ITC during intuitive inquiry meditation when viewing their own image. Both the results of ERSP and ITC may indicate that monks had greater dynamics in terms of ERP perturbation analysis than the beginner participants during different conditions when they viewed their own images. The difference was most significant at the time window of 180-220 ms, and at theta wave and alpha wave (4-8Hz, 8-12 Hz).

Discussion

The result of this ERP study revealed that intuitive inquiry meditation (Chan/Zen meditation, Can-Hua-Tou) could specifically alter a meditator’s response to concept of self, when viewing the stimuli of one’s own image and an image of the Buddha, which represent the two important concepts in Buddhism. There was a double dissociation between experienced practitioners (monks) and beginner practitioners (layman control) in this ERP experiment. It implies that training of this form of intuitive inquiry meditation which involves critical thinking and the intuitive doubting processes, at different levels of practice, may induce different pattern of brain activities when viewing the same two groups of images.

The beginners demonstrated a reduced neural response to the Buddha image in the inquiry condition when compared to that observed in the normal condition. There was no such difference between the two meditation conditions when participants viewed their own images. In contrast, the monks demonstrated a reduced neural response only to their own images when comparing the outcomes of the intuitive inquiry meditation condition to those of the normal condition of no meditation.  However, this difference disappeared when these experienced participants viewed an image of Buddha. This result reveals an apparent difference in brain activation during intuitive inquiry meditation which indicates that experienced meditators and laymen may have conceived the meditative objects differently. This result reveals an apparent difference in brain activation during intuitive inquiry meditation which indicates that experienced meditators and laymen may have conceived the meditative objects differently, thus adding to our understanding of neural markers for long-term intuitive inquiry meditation. [reviewer 3]

In addition, when compared to experienced monk practitioners, laymen had a difference in the P300 component, which indicates an attentional process for relatively rare events (Herzog et al., 2021; Lindenbaum et al., 2021). A previous study found that mindfulness meditation induction can improve accuracy in an attention task, accompanied by a larger P300 amplitude (Lakey et al., 2011). This shows that during inquiry meditation, the target of laymen’s doubting processing is more specifically focused on the concept of Buddha’s image. This phenomenon might be unique to Buddhist intuitive inquiry mediation due to its earnestly toward the search for enlightenment.[reviewer 3]  This implies that during inquiry meditation, the target of laymen’s doubting processing is more specifically focused on the concept of Buddha’s image. This phenomenon might be unique to Buddhist intuitive inquiry mediation due to its earnestly toward the search for enlightenment. During the search, practitioners are required to examine the ‘original face’ of everything, including the ultimate authority of the religion, the Buddha. The inquiry and doubting process of the concept of Buddha is emphasized in a specific group of Buddha texts, the Perfection of Wisdom. For example, in the Diamond Sutra, it states that the Buddha cannot be conceived by his appearance, nor his voice, as relying on the outer appearance of the Buddha is an incorrect way to perceive and understand the true nature of the Buddha.

For participants in the monk group, however, the effect of enquiry in the doubting process is more focused on the concept of self. It indicates a shift in meditation targets and focuses more on ‘self’ as an internal concept, suggesting a greater flexibility in self-schema processing. Indeed, in Buddhist practice and theory, the self is the ultimate concern that needs to be addressed and let go of, and ultimate enlightenment can only be reached by breaking the attachment to the concept of the self and attaining anatta (nonself) (Hongladarom, 2017; Martinezgomez, 1984). In the Buddhist tradition, the attachment to the concept of self is the most difficult to break through. In the monk group, the ERP result showed that the difference between the meditation and normal conditions is in the N170/P100 period, an early component for face recognition (Desjardins et al., 2013; Ganis et al., 2012). This ERP result indicates that monks might have altered neural responses to images at the early stage of face recognition, probably due to a top-down process. After long-term intuitive inquiry meditative practice, i.e., pondering ‘Who is chanting the name of Buddha?’, monks might be able to quickly and intuitively alter the mental representation of self-related information processing. The monks' ERP result, showing a difference in the N170/P100 period—an early component for face recognition—when viewing their own images in different conditions, indicates that monks might have altered neural responses to images at the early stage of face recognition, probably due to a top-down process. This shows that after long-term intuitive inquiry meditative practice, monks might be able to quickly and intuitively alter the mental representation of self-related information processing.[reviewer 3]

According to false tagging theory, monks might have denounced the schema of the self by the doubting process induced by the priming question ‘Who is chanting the name of Buddha?’. Once the doubting process tags the concept of self as false and/or illusory, the self-importance of the self-image is no longer a target of interest, and the automatic cognitive processing of the concept of the self is reduced, thus requiring fewer cognitive resources. In Buddhist theory, the self is merely an assembly and aggregation of a variety of components under favourable conditions. Thus, there is no fundamental essence in the concept of self and it could be subjectively dismantled by careful dyslectic analysis (Jones, 2021).

The layman beginners could be less effective in exercising this doubting process, and their practice was less profound. Therefore, they could still be focusing on and continue to attach to external concepts, including the Buddha concept. The effect of intuitive inquiry meditation is mainly found in the P300 component when viewing an image of Buddha. The P3 component refers to attention resources for cognitive evaluation. The P300 component in the current study refers more to P3b as the images were all the same and repeated 60 times in one condition, 120 times in total in the two conditions. P3 has both P3a and P3b components (Polich, 2007). The P3a component is referred to as novel P3, which is attributed to more automatic response processing, probably at frontal lobe generator sites (Kam et al., 2021; Kramer et al., 2011). The P3b component is associated with more effortful information processing, which is maximal at the posterior sites (Milligan et al., 2019; Segalowitz et al., 2001). In this paper, as the stimuli were always repetitive, the results would reflect the attention allocation process and memory engagement. A previous study found that increased P3b-like amplitude is associated with successful memory encoding and storage (Azizian et al., 2007). It is plausible that the evaluation of an image of Buddha engages focal attention, which further facilitates the context-maintenance and subsequent memory operation of the concept of Buddha (Gonsalvez et al., 2000; Polich et al., 2003). A reduced P3 amplitude during the intuitive inquiry meditation condition implied that laymen allocated fewer cognitive resources to encode the image of Buddha. In contrast, monks showed little difference in processing the Buddha image in the inquiry condition versus the normal condition. It is conceivable that the doubting exercise of these experienced monks might have already passed the early stage of cognitive processing of external stimuli, including the image of Buddha.

Some scholars have said that Buddhism as a religion is unique in terms of belief (Hexham, 2011). While most other religions depend heavily if not solely on belief, Buddhist practices would urge practitioners to not blindly believe and become attach to any concept and to raise doubt and inquiry into every concept, even the concept of Buddha. Practically, this doubting practice has two purposes in intuitive inquiry meditation: first, doubt can be raised in any concept and term. As described by the Buddhism doctrine, every external phenomenon and internal reflection is not independent and thus is eventually subjected to change and deterioration. Second, the doubt process itself can be an object of meditation, so there would be additional metacognition to monitor this ongoing doubt process (Buswell, 2018).

In the experienced monks, the object of intuitive inquiry meditation seems to have shifted to the more fundamental concept of ‘self’, a form of metacognition that involve deep reflexive ability. The ERP results showed the greatest reduction in the ERP component in the N170/P100 stage when monks processed images of themselves. Face recognition can induce an N170 component in the temporal-occipital region, accompanied by a more frontal positive component, referred to as P170, or more common vertex positive potential (VPP) (Jaworska et al., 2012; Jeffreys, 1993). P170, like N170, is mostly related to perceptual processing for face recognition and attentional reallocation. However, P170 has a different feature and occurs in a more frontal region. For example, the frontal P170 component is not observed in children 7-8 years old, although they do have an N170 component elicited by face recognition. P170 only begins to occur in adolescents and becomes stable in adults (Taylor et al., 1999). A recent ERP study on insight found that frontal P170 increases when individuals face cognitive challenges, such as riddles (Wang-Bing et al., 2012). A subsequent study also showed that P170 and P2 alike may reflect an unconscious metacognitive monitoring process. According to the dual-process framework of metacognition, metacognition has two processes: metacognitive feelings that are mainly based on nonanalytic processes, and metacognitive judgements that are based on analytic processes (Koriat et al., 1999). Additional ERP studies on insight also suggest that the P170 component may be related to the capacity of the human instinct without much conscious processing involved at an early stage of information processing (Ashwell et al., 1996; Bullock et al., 1994; Liang et al., 2020).

In the current study, monks demonstrated greater frontal P170 amplitude when viewing images of themselves in the normal condition than in the inquiry condition. For these monks who have been devoted to intuitive inquiry meditation for many years, it is plausible that even in the normal condition, they engaged in doubting processing for their own images, while when it came to the inquiry condition, they might have already reached a state of detachment from his own identity. Intuitive inquiry meditation as a practice of wisdom aims to directly contemplate and analyse the issue of ‘self’ and attain a state of ‘nonself’, which states that self-identity is no more than an assembly of dependent conditions (Austin, 2012, 2013).

After long-term practise, monks demonstrated greater dynamics between the different conditions. According to the ERSP results, monks showed the greatest reduction in perturbation in the theta band when viewing images of themselves in the inquiry condition compared to that in the normal condition. Of note, theta band activity is frequently found in various tasks of memory and cognitive control (Rossi et al., 2014). A reduction in theta waves during the inquiry condition may indicate a lower demand for cognitive resources, probably due to the practice of inquiry meditation. By contemplating the impermanence of the nonself, monks can quickly let go of the obsessive concept of the self. Theta waves have been frequently found in cognitive control and cross-frequency coupling, especially in deeper brain regions, such as the hippocampus. One previous EEG study found that theta phase-gamma amplitude coupling plays an important role in cognitive processing and reflects information processing and signal interaction across distant brain regions (Ahn et al., 2022).

At the same time, ITC results showed the greatest reduction in the inquiry condition compared to that in the normal condition when viewing one’s own image. ITC represents the trial-to-trial coherence of brain processing of similar stimuli, indicating the stability of the neural response. (Barios et al., 2017; Gao et al., 2018). A higher ITC implies a more stable response, while a lower ITC indicates that less attention was given to specific stimuli during neural development and in cases of neuroplasticity (Crowley et al., 2014). These differences were not observed in beginners. The results of ERSP and ITC demonstrate a more dynamic spectrum perturbation among experienced monks across different tasks compared to that of beginners. This reflects that monks can flexibly amass their cognitive dynamics on a specific task while greatly reducing them during intuitive inquiry meditation. This feature and capacity follow well with the Buddhist emphasis the wisdom of nonattachment and letting go since all phenomena are impermanent, including oneself. Thus, it is imperative to be dynamic and flexible when dealing with ongoing events.

Due to greater cognitive flexibility, monks demonstrated a similar brain response to either an image of Buddha image or themselves. The layman beginners showed an apparent difference in brain responses to an image of Buddha image and themselves. This difference between groups remained significant. This illustrates that experienced monks can reach a state of equanimity toward the two stimulus (Kraus et al., 2009) and evenness of mind even under attention-arising concepts, such as Buddha and the self. Thus, even in the layman control group, the difference between the responses to images of oneself and of Buddha was smaller in the inquiry condition than in the normal condition. The difference between images of oneself and Buddha was also obvious among monks when they viewed in the normal condition. This again reflects the capacity of monks to manipulate their cognitive processing of images more dynamically, as have suggested by the Buddhist theory of wisdom of non-attachment.

As Anattalakkhana Sutta (in Pali) repeatedly emphasizes, all phenomena, whether external or internal, in the mind or body, have characteristics of impermanence and non-essence (self) (Jota, 1951; Thvanʻʺ, 2006). Nothing is truly dependable or reliable, nor can anything be claimed to be ‘mine’ all the time, nor is there a real and unchanging ‘me’. Thus, suffering cannot be prevented due to this impermanence and lack of self. By reflecting on this understanding, practitioners can become more aware of the true nature of Buddha and the self, although the sophistication and emphasis are different between beginners and experienced monks, as demonstrated by our ERP results.

Under intuitive inquiry meditation, monks demonstrated the ability to reduce the difference between self and other concepts, including Buddha. This contrasts with layman beginners in which the difference between the self and Buddha images remained significant during the inquiry condition. This result indicates that beginners could not eliminate the difference between different concepts, such as self, other, Buddha, etc., as well as the experienced meditators could.

One limitation is worth noting in the current study. The intuitive inquiry meditation is usually a mind pondering and doubting process. This can be better measured in a relatively longer period. This ERP experiment might be too short to capture the full-scale brain activity induced by inquiry meditation. A long experiment paradigm or a similar functional magnetic resonance imaging can better illustrate the neural correlates of intuitive inquiry meditation, especially those in the subcortical regions. Another limitation is that half of the layman participants had their experiments done in an EEG laboratory, while all the monks took the experiment in a temple. The experiments were limited by the time constrain during an inquiry meditation retreat, which lasted 7 days, so it was not feasible to collect all the data within that short period of time.

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