A Glimpse into the Meditating Brain

A Glimpse into the Meditating Brain*

Bryan Williams

University of New Mexico

via A Glimpse into the Meditating Brain.

 

A Glimpse into the Meditating Brain*

 

Bryan Williams

University of New Mexico

 

 

Abstract: Meditation has served as a traditional Eastern technique to transform consciousness and gain higher insight by focusing attention and introspectively observing one’s own mental processes. Some research now suggests that regularly practicing meditation may also benefit health and well-being by helping to calm the mind and body. With encouragement from the Dalai Lama, neuroscientists are currently studying the meditating brain in order to learn more about how it works, how it changes, and how it can promote mind-body health. In this paper, a basic overview of the latest findings relating to the possible brain correlates of meditation is presented, and the implications of these findings for health and the psychological quest to better understand subjective conscious experience are discussed.

* This paper is an extended version of an invited talk given at the Morning Star Center for Spiritual Living, Norman, OK, June 7, 2009. My appreciation goes to Dylan Oaks for his help and support, and to Grant Lacquement for permission to cite his work and for lending useful resource material.

 

1. Introduction

In seeking to deal with the stress and demands that come with the challenges of everyday life, many people now find solace in the momentary respite often attained through the practice of meditation. According to a recent survey by the National Center for Health Statistics in Maryland (Barnes, Bloom, & Nahin, 2008), meditative practice among adults has significantly increased from 7.6% in 2002 to 9.4% in 2007, making it one of the most commonly used complementary and alternative therapies in the United States. It is currently estimated that there are about 10 million American meditators, and hundreds of millions around the world (Walsh & Shapiro, 2006, p. 227).

Various forms of meditation are known to exist, but most forms can be generally grouped into one of two classes for the simple purpose of distinction (see Table 1 below). The first class is often called concentrative meditation, in which attention is focused on a particular object, image, word, sound, or bodily process, such as breathing. The second class is often called mindfulness meditation, which involves expanding attention in a passive way to allow broader awareness of one’s own mental processes. In other words, one expands their inner awareness and introspectively observes their thoughts, emotions, and bodily sensations. This inner focusing can help filter out extraneous distractions that can potentially interrupt the exploration of higher mental states and the attempt to gain insight. The boundaries between these two classes should not be considered fixed, however, as some forms of meditation can and do blend techniques from both classes (Goleman, 1988).

Although they tend to differ from one another in terms of technique, philosophy, and outcome, recent research suggests that the various forms of meditation may share one important commonality: they appear to beneficial for health and well-being. For example, volunteers who practiced a simple mantra (word)-based concentrative meditation technique twice a day showed a significant reduction in stress and negative mood after three months (Lane, Seskevich, & Pieper, 2007). In addition, a practitioner of Transcendental Meditation (TM) once stated: “I often feel an increased calmness in tense situations where I work. Even my co-workers say they don’t understand how I can be so calm. It’s all due to meditation” (Ferguson, 1975, p. 17). Other study findings suggest that Yoga and various forms of mindfulness meditation may provide supplemental benefit for the treatment of stress, mood, and anxiety symptoms (Arias et al., 2006; Chiesa & Serretti, 2009; Davidson et al., 2003; Grossman et al., 2004; Ivanovski & Malhi, 2007; Oman et al., 2008; Shapiro et al., 1998; Walsh & Shapiro, 2006).¹

 

Table 1. The Two Classes of Meditation and Some of Their Various Sub-Forms

Class/Form	Brief Description
Concentrative:
Transcendental Meditation (TM)	A 20- to 30-minute practice usually done twice daily, in which the meditator focuses attention on a specific word, image, or sound (called a mantra) that is traditionally obtained from the Sanskrit language. Originally derived from ancient Vedic tradition by Maharishi Mahesh Yogi.
Yoga Meditation	Originally derived from ancient Hindu culture, various types exist (e.g., Tantric, Hatha, Kundalini, Qigong, Sahaja, Nidra, Samatha). Each type utilizes its own techniques in body posture (asana), breath control (pranayama), focused image or idea attention (dharana), and contemplation (dhyana) to move toward a goal of achieving the state of Samadhi, a union with the “Universal Self.”
Meditative Prayer	A form of religious contemplation seen in Christianity, Judaism, and Islam, wherein a devout practitioner focuses their attention on a certain phrase or prayer from a given religious text (e.g., the Bible, the Koran) with the goal of opening themselves to, and attaining oneness with, a certain divine entity (e.g., God, Christ, Allah).
Mindfulness:
Zen Meditation (Zazen)	Originally derives from the Mahayana school of Buddhism found in Chinese, Japanese, and Korean culture. Following the philosophy of Zen Buddhism, the practitioner’s goal is to enter Satori, a state of enlightenment in which they become fully attuned to the reality both inside and outside their body, and they gain the ability to ask the appropriate questions concerning these realities. To gain the insight needed to understand the answers, the practitioner practices meditating on a traditional riddle or puzzle (known as a koan).
Vipassana (“Insight”) Meditation	A practice derived from the Theravada Buddhist tradition of Thai and Burmese culture, wherein the practitioner passively observes their present thoughts and bodily sensations with the goal of increasing equanimity, a state of passive acceptance that relies on awareness of these thoughts and sensations.

The potential benefits of meditative practice may stem in part from its ability to help calm the mind and body. Physiological monitoring of novice TM meditators has often revealed notable drops in their breathing rate, oxygen intake, and heartrate during meditation, along with a rise in their skin’s electrical resistance. This suggests that, as they are meditating, these individuals gradually become calmer and experience a drop in body metabolism (Davidson, 1976; Ferguson, 1975; Travis & Wallace, 1999; Wallace, 1970; Wallace & Benson, 1972; Wallace et al., 1971; West, 1979; Woolfolk, 1975).² Studies of novice Yoga and Zen meditators have found similar drops in breathing rate and/or oxygen intake, while skin resistance either tends to rise or become more stable, again suggesting a calming state (Corby et al., 1978; Elson et al., 1977; West, 1979; Woolfolk, 1975). As we shall see in Section 4, the physiological effects of practice may be more complex for advanced meditators.

Another potential benefit of meditative practice is that it appears to be effective in improving one’s attention. Cognitive studies find that novice mindfulness and TM meditators tend to perform better than non-meditators on attentional tasks, and they tend to be less affected by distracting stimuli (Chan & Wollacott, 2007; Moore & Malinowski, 2009; Tang et al., 2007). Meditators also tend to notice fast-moving stimuli that other people may miss (Lutz et al., 2008; Slagter et al., 2007).

All of these findings naturally lead to a valuable question: What might be going on in the mind, and thus the brain, of a meditator to produce these behavioral effects? Recently, this question has intrigued the minds of neuroscientists, psychologists, Buddhist scholars, and even the Dalai Lama. During an invited address at the 2005 Annual Meeting of the Society for Neuroscience, His Holiness expressed an interest in the matter and encouraged neuroscientists to further explore the meditating brain in order to learn more about how it works, how it changes, and how it may lead to better therapies for mind-body health (Fields, 2006; Talan, 2006).

There may be another valuable reason for studying the meditating brain. Some advanced meditators have spoken of entering what have been called “deep” or “higher” states of meditation, an experience that has also been described in Yogic lore and Buddhist spiritual tradition. During such states, many meditators can often have a profound experience of transcending the physical and mental boundaries of their own individual self. For example, a mindfulness meditator described his transcending experience during the deep state in the following manner:

 

I am usually aware of the boundary of my body against the skin and you lose that sense in Dhyana…you become a kind of…field of energy, the boundaries of which are not clearly delineated (Gifford-May & Thompson, 1994, p. 124).

A meditator practicing TM felt as though the center of his being was expanding outward in a physical way. According to him, the experience felt:

 

…literally as though my arms were extended and they extended to the reaches of the universe…whatever that was…a kind of immeasurable distance…my head would feel incredibly expanded and huge…as if it were capable of being the size that a galaxy could fit into…and so that sense of being enormous and yet not out of my body…but expanding out from there in all directions, infinitely (p. 125).

During transcendence, some meditators may describe encountering a different sense of reality. One of them described this as a:

 

…field of awareness that is cosmic…there was no sense of limitation, there was just awareness…endless, boundless, oceanic (p. 126).

A female meditator described her encounter in terms of a sense of a higher power:

 

…it’s like a place…it’s very, very powerful…it has an energy about it…that I don’t have in my life…and suddenly you find this…it’s like…”Holy schmoly! What have I stumbled on now? What is this energy?” (p. 127, italics in original)

Some may also describe feeling intense bliss, rapture, and/or deep calmness throughout the deep meditative state (pp. 128 – 129).

Vipassana meditators sometimes relate experiences similar to those seen in deep states during intense training retreats, along with spontaneous body movements and perceived changes in their body image (Kornfield, 1979). Grant Lacquement (2008) states that meditative prayer can uncover a “larger awareness and connection” that is always present, as well as facilitate connection with a higher divine presence. This seems akin to experiencing a higher sense of reality.

These experiences that meditators report having during deep states suggest that they may be briefly experiencing an aspect of conscious awareness beyond that of their ordinary, everyday awareness. If that is the case, then what areas and functions of the brain might be associated with the deep meditative state?

This is another valuable question that has apparently sparked the interest of the Dalai Lama. To encourage exploration into the issue, His Holiness has hosted several research conferences in order to foster a dialogue between neuroscientists and Buddhist scholars, which may allow them to see where their respective disciplines intersect when it comes to exploring the nature of the mind (Barinaga, 2003; Knight, 2004).

This paper provides an overview of what neuroscience has tentatively learned so far about the meditating brain, and briefly discusses what these lessons could mean for mind-body health and the broader psychological quest to better understand conscious experience. But before we can begin to explore the meditating brain, it is imperative to briefly survey the territory that we will be venturing into.

 

2. The Brain: Mapping the Territory

My mentor William G. Roll, a retired professor of psychology at the University of West Georgia, once suggested that exploring the brain is akin to the trip that Marco Polo took to China around 1275. Like the world at that time, several parts of the brain are pretty well understood, while other parts still harbor hidden, undiscovered valleys. A foray into this new territory requires a basic map that other people can follow, so that they do not lose the trail along the way. A map suitable for our purposes is shown in Figure 1.

 

 

 

Figure 1. A basic map of the human brain, with each of its major lobes and cortices indicated (see text for details).

The adult brain weighs a little more than three pounds. At its base is the brainstem, a narrow stalk of tissue connected to the spinal cord that contains bundles of nerve cells, or neurons, which are vital for keeping us alive and conscious. Blossoming out of the back of the brainstem is the cerebellum, a convoluted mass of neural tissue that helps maintain body balance and muscle coordination. Perched above the brainstem and the cerebellum is the largest part of the brain, called the cerebrum. Its upper layer of tissue, called the cerebral cortex, is comprised of 70 to 100 billion neurons (Schneider & Tarshis, 1995, p. 83). The cortex only 3 to 5 millimeters thick, but it takes up more than a third of the brain’s volume because it is folded like the shell of a walnut into a maze of hills and valleys.

The cerebrum can be divided into four individual lobes (frontal, parietal, temporal, and occipital), each of which is specialized to handle certain behaviors. The frontal lobe plays a prime role in our ability to make decisions, plan our actions, and coordinate our movements. In connection with this, the rear of the frontal lobe contains the primary motor cortex, one of the central brain areas involved in movement. When the motor cortex is damaged, a person can have difficulty making fine movements with their fingers and limbs (Kolb & Whishaw, 1990, Ch. 19).

Directly behind the lower part of the frontal lobe is a cortical area that will be relevant to our discussion of certain forms of meditation. This area, which has a shape similar to that of a crescent moon, is known as the anterior cingulate cortex. In addition to being involved in some forms of attention and complex thought processing, some research suggests the anterior cingulate cortex is also involved in regulating some features of the autonomic nervous system, including heart rate, breathing rate, and blood pressure (Devinsky et al., 1995, pp. 287 – 288).

The parietal lobe appears to play a role in both sense and spatial perception. Toward its front is the somatosensory cortex, which receives and analyzes information relating to pain, pressure, touch, and temperature from all parts of the body. When it is electrically stimulated, a person may feel a tingling sensation in their skin, or they may suddenly have the feeling of being lightly touched.

Toward the back of the parietal lobe is a small sub-region called the superior parietal lobule, which becomes active when people try to visually determine the location, depth, and trajectory of objects in physical space (Cohen et al., 1996; Haxby et al., 1991; Sack et al., 2002). It can also be activated when people shift their attention toward a particular point in space (Corbetta et al., 1995; Posner & Rothbart, 1991). Given its role in spatial perception, the parietal lobe has been considered the “where” pathway in visual signal processing (Linden, 2007, pp. 86 – 89). This area may also be relevant in our discussion of certain forms of meditation.

The inner reaches of the temporal lobe are the domain of the hippocampus and the amygdala, the two structures at the heart of memory and emotion, respectively. The temporal lobe is also involved in hearing, as it contains the auditory cortex, the chief brain area for sound and speech processing.

In the back of the brain is the occipital lobe, which contains the primary visual cortex, where signals from the eyes are processed. Upon receiving electrical stimulation of their visual cortex, people have reported seeing a bright flash of light or even swirls of color. People with an impaired visual cortex can be “mentally blind,” meaning that they are often unable to perceive objects in front of them, even though their eyes still respond to their presence (Kolb & Whishaw, 1990, pp. 228 – 238).

 

2.1. Imaging the Brain

Our ability to learn about the specialized abilities of the four lobes has greatly improved over the past few decades through advances in brain imaging technology. These advances have been immensely valuable for medicine and neuroscience because they allow us to electronically peer through the skull and glimpse the brain as it partakes of behavior. So far, three kinds of advanced technologies have been used to study the meditating brain: functional magnetic resonance imaging (fMRI), positron emission tomography (PET), and single-photon emission computed tomography (SPECT).

Unlike the purely static image of the standard MRI, fMRI provides ongoing impressions of working brain function in relation to behavior. To do this, many fMRI studies commonly use a technique known as blood oxygenation level dependent (BOLD) hemodynamic response. As implied by its big name, BOLD measures the amount of oxygen in the brain as a result of cerebral blood flow. Based on the idea that the brain regions which have the most oxygen-rich blood are the ones that are the most neurally active at the moment, BOLD measurements allow us to estimate the level of neural activity in a particular brain region during a specific behavior. This in turn allows us to infer which regions may be functionally associated with that behavior (Buxton, 2001, Ch. 16; Logothetis, 2008).

In a PET scan, a person is intravenously injected with a liquid (called a tracer) that contains a weak radioactive isotope. As its name implies, the tracer traces a path through the brain as it courses through the bloodstream, gradually emitting positrons as the isotope decays. When they interact with other subatomic particles, these positrons produce X-rays that can be detected, counted, and mapped using a digital scanner. Similar to fMRI, PET follows the idea that the brain areas with the highest amounts of blood are the most neurally active at the time (Kolb & Whishaw, 1990, pp. 123 – 126; Schneider & Tarshis, 1995, pp. 95 – 96).

A SPECT scan proceeds in nearly the same way as a PET scan, except that instead of X-rays, the scanner detects the individual photons that are gradually emitted by different kind of tracer. Through a reaction with the chemicals found in neural tissue, the tracer is briefly retained by the brain and thereby provides a snapshot of the brain’s metabolic activity (Kolb & Whishaw, 1990, p. 126; Warwick, 2004).

 

2.2. Brain Waves

In addition to imaging techniques, it is possible to study the meditating brain by monitoring its electrical activity. The electrochemical activity of the billions of neurons found in the brain produces a continuous stream of electric waves that are emitted from the surface of the cerebral cortex. These brain waves, as they are called, can be observed and recorded using a device called an electroencephalograph (EEG).

To record a person’s brain waves by EEG, small metal disks capable of conducting electricity (known as electrodes) are attached to the scalp at various places around the head to detect the brain waves traveling up from the underlying cortical surface. Brain waves are quite weak, registering only about a thousandth of a volt, so they must be amplified by the EEG before being recorded as a series of jagged lines on a moving paper chart.

There are five types of brain waves that are distinguished by their frequency, measured in cycles per second, or Hertz (Hz): Delta waves (1 – 3 Hz) have the slowest wave cycles, and commonly appear when we are in a deep sleep. Theta waves (4 – 7 Hz) can also be present during sleep, usually when we start to feel drowsy and fall into a light sleep (Carlson, 1992, pp. 242 – 243). Alpha waves (8 – 12 Hz) are typically present during a state of relaxed awareness, when our minds are not actively engaged in deep thought. Beta waves (13 – 29 Hz) appear when we are actively thinking, alert, and attentive (Schneider & Tarshis, 1995, pp. 412 – 413). Gamma waves (30 – 80 Hz) have the fastest wave cycles, and often arise when we are mentally integrating and processing complex sensory information (Desmedt & Tomberg, 1994; Joliot et al., 1994).

 

3. Studies of the Meditating Brain

With our survey of its territory complete, we shall now look at what goes on inside the brain during various forms of meditation, based on experimental findings. It should be kept in mind that, unless noted, the experiments described in this section were done with novice and intermediate meditators who only have practiced for a relatively short time (anywhere from six months to four years). Advanced meditators with longer training histories seem to constitute a special case in terms of their physiology and depth of meditation, so we shall look take a closer look at them in Section 4.

 

3.1. Transcendental Meditation

As we saw in Section 1, several research findings suggest that people who practice TM can physiologically experience a calming effect in their body while meditating. But what is happening in their brain during that time? Various EEG studies indicate that as they sit quietly with their eyes closed and focus on their mantra, many TM meditators show a steady pattern of alpha waves. A small number of them may show a drop in wave frequency to the lower part of the alpha spectrum (8 to 9 Hz), followed by the brief appearance of a theta wave pattern (Banquet, 1973; Cahn & Polich, 2006; Davidson, 1976; Ferguson, 1975; Jevning et al., 1992; Stigsby et al., 1981; Wallace, 1970; West, 1980; Woolfolk, 1975). These patterns are often recorded from electrode sites located over the frontal lobes and near the brain’s midline (Wallace et al., 1971). This suggests that, as they meditate, the brain waves of TM practitioners tend to gradually slow down and approach frequencies that are typically associated with low mental arousal, which would be consistent with a calming effect.

In addition, some TM practitioners may show patterns of synchronized brain waves, a phenomenon often known as EEG coherence (Ferguson, 1975, pp. 22 – 25; Jevning et al., 1992, p. 419; West, 1980, pp. 370 – 371). In order to better grasp the concept underlying this phenomenon, we might consider the following illustrative example: Let’s say that we simultaneously recorded the EEG activity from two different regions of our brain, and then compared them afterward to see if they show any similarity. Most of the time, during our ordinary conscious state, we would find that these two EEGs are a mixed-up bunch of waves scattered across several different frequencies, with little to no similarity at all. However, if we repeated the process with a TM practitioner while he or she was in a deep state of meditation, we might find that their two EEGs show a fair degree of similarity, with the two wave patterns appearing to be in close alignment with each other (Figure 2). As we shall see in Section 4, this phenomenon tends to be more common among advanced meditators.

 

Figure 2. A comparison of the EEGs of a non-meditator (top) and a TM meditator (bottom). While the brain waves of the non-meditator are largely scattered across different frequencies during the ordinary waking state, those of the meditator show a consistent pattern of synchronization around 20 Hz during a deep meditative state (Ferguson, 1975).

At least one imaging study has been done to further explore the areas of the brain that may be active during TM (Jevning et al., 1996). Changes in cerebral blood flow were monitored in 34 meditators as they focused on their mantra. Compared to control volunteers who merely sat and relaxed, the meditators showed increased flow in their frontal lobes, a finding consistent with the EEG patterns recorded in that same region (Wallace et al., 1971). The meditators also showed increased flow in their occipital lobes, which would be in line with the act of visualizing their mantra.

 

3.2. Yoga Meditation

Several types of Yoga meditation are known to exist, and to date, EEG and imaging studies have examined the brain’s activities during five types: Tantric, Kundalini, Sahaja, Nidra, and Iyengar.

Similar to TM, Tantric Yoga is marked by the attentional focus on a specific mantra, with the goal of attaining unity with it. In two studies (Corby et al., 1978; Elson et al., 1977), brain wave activity was monitored in Tantric meditators as they sat in the lotus position and focused on the sound of a two-syllable Sanskrit word mantra. Compared to relaxing control volunteers, meditators with an average of 1.5 to 2 years of training had produced higher amounts of alpha and theta activity along the brain’s central midline. While many of the volunteers became relaxed to the point where they would fall asleep, the steady alpha and theta patterns seen on the meditators’ EEGs suggests that they were able to enter and maintain a mental state close to the boundary of wakefulness and sleep, yet still remain awake.

Kundalini Yoga can also involve focusing on a mantra while passively observing one’s breathing. In one imaging study (Lazar et al., 2000), meditators with four years of Kundalini training underwent fMRI scanning while they silently repeated a two-phrase mantra in time with their breaths. During a control period, the meditators did not observe their breaths and turned their attention away from the mantra by silently thinking up a list of animal names. Compared to this control period, more neural activity was seen during the meditation in the anterior cingulate cortex. In the late stages of the meditation, the frontal, parietal, and temporal lobes became active. This suggests that brain regions associated with attention and control of autonomic nervous system are involved in this Yoga type.

Rather than mantra focusing, Sahaja Yoga emphasizes focusing one’s attention inward on internal processes and suppressing all other extraneous thoughts, which is meant to help open the way to the experience of an internally “blissful” state. In two studies (Aftanas & Golocheikine, 2001, 2003), EEGs were recorded from both novice (less than six months of training) and advanced (3 to 7 years) Sahaja meditators as they attempted inward focus to reach the blissful state. Compared to the novices, the advanced meditators showed much more theta activity over their frontal lobes and the midline of their brains, and they reported more intense feelings of bliss. In contrast, the novices showed more alpha waves over their occipital lobes and the rear part of their parietal lobes (Figure 3). This suggests that the achievement of slower brain waves may partly be a function of meditation training history, a possibility we shall examine further in Section 4.

 

 

Figure 3. A comparison of the brain wave activity of novice (STM, left column) and advanced (LTM, right column) Sahaja Yoga meditators, looking down from the top of the head. Whereas novices show more alpha in the occipital and rear parietal lobes (lower left), advanced meditators show more theta in central region of the frontal lobes (top and center right) (Aftanas & Golocheikine, 2003, 2005).

Instead of focusing their attention, Yoga Nidra meditators adopt a more neutral technique, wherein they “withdraw” from the desire to act and passively observe the bodily sensations and visual images that arise in their mind. In two imaging studies (Kjaer et al., 2002; Lou et al., 1999), meditators who had more than 5 years of Yoga Nidra training underwent PET scanning as they received a guided meditation. As they were guided to imagine the sensation of weight on various parts of their body, several areas including the frontal lobe and the anterior cingulate cortex were activated in the meditators’ brains. Then, when guided to visualize a serene rural landscape in summer, visual regions in the occipital lobe became active. Finally, as they attempted to generate a mental representation of their self, areas surrounding the superior parietal lobule lit up with activity. Monitoring of the meditators’ brain waves further revealed increases in theta activity during the meditation, and the PET scans indicated a higher release of dopamine, a neurochemical sometimes associated with feelings of pleasure (Schneider & Tarshis, 1995, p. 154). In line with the ideas of Yoga Nidra, several of the meditators reported a reduction in the conscious control of their attention, as well as a “loss of will.” This was counteracted by an experience of intense sensory imagery.

Iyengar Yoga combines meditation with the breathing and body posture exercises that are commonly associated with the term “yoga.” In a study using SPECT (Cohen et al., 2009), the brains of four people were examined before and after they received a 12-week Iyengar training program in order to see how they might change. Compared to before their training, the four individuals showed higher blood flow changes in their frontal lobes after the 12 weeks of training. As we shall see in Section 4, a change in the brain as a result of meditation training is one of the things that may distinguish advanced meditators from novices.

 

3.3. Meditative Prayer

Various forms of meditative prayer can be seen across several different religions, although it is the Christian-based form that has been the focus of two recent imaging studies.

In the first study (Azari et al., 2001), 6 religious school teachers from a German Evangelist community received a PET scan while they attempted to briefly enter a religious meditative state by reciting the first verse of Psalm 23 in the Bible. Compared to 6 non-religious control volunteers, the teachers showed higher activation in two areas of the frontal lobe associated with attention and the reflexive evaluation of thought (Figure 4).

 

 

Figure 4. Averaged PET scan results from 6 Evangelist teachers engaged in meditative prayer, indicating increased cerebral blood flow in the forward and central regions of the frontal lobe (Azari et al., 2001).

In the second study (Newberg et al., 2003), SPECT images were obtained from three Franciscan nuns who had more than 15 years of practice with “centering prayer,” in which they continually focus their attention on a prayer or a phrase from the Bible, which is meant to help them achieve the experience of “opening themselves to being in the presence of God” (p. 626). During such a profound experience, the nuns sometimes describe having “a loss of the usual sense of space” (p. 626). Compared to a resting state, the nuns’ brains showed higher amounts of cerebral blood flow in various regions of the frontal lobe. In addition, an inverse relationship was observed between the blood flow in the frontal lobe and the blood flow in the superior parietal lobule, such that as the flow in one increased, the flow in the other decreased (and vice-versa). Given its apparent role to spatial perception (Section 2), the blood flow changes in the superior parietal lobule may be related to the nuns’ experience of losing a usual sense of space.

 

3.4. Zen Meditation (Zazen)

To explore the brain physiology of mindfulness meditation, several studies have directly focused on one of its sub-forms: Zazen, the sitting meditation of Zen Buddhism. During the practice of Zazen, the meditator sits cross-legged on a round cushion with their hands enclosed. Keeping their eyes open, the meditator casts their gaze downward to look about one meter ahead as they centrally ponder a koan.³ The aim is not necessarily to produce an answer to the koan, but rather to gain the focus necessary to achieve the enlightened state of Satori (see Table 1). Occasionally, a meditator may go through an intensive training period known as Sesshin, in which they practice Zazen 8 to 10 times a day for approximately one week.

In one of the earliest studies (Kasamatsu & Hirai, 1966), the brain wave activity of 16 Zen priests and 32 of their disciples was recorded during a period of Sesshin at a traditional Zen Buddhist training hall. While meditating, novice disciples with 1 to 5 years of Zazen training were found to produce a steady pattern of alpha waves, even with their eyes open.⁴ More intermediate disciples with 5 to 20 years of training had a tendency to exhibit a slowing of their brain waves, as indicated by drops in alpha wave frequency. (We shall look at the priests in Section 4.)

Three recent EEG studies of Zazen have been geared toward examining Su-soku, a training technique usually given to Zen Buddhist initiates to help them adapt to the practice of Zazen (Kubota et al., 2001; Murata et al., 2004; Takahashi et al., 2005). During Su-soku, the initiate focuses all of their attention on their breathing, usually by counting each of their breaths as they inhale and exhale at a steady rate.⁵ To see how this practice of this technique might affect the brain, Japanese researchers briefly instructed three groups of college student volunteers in Su-soku, and then recorded their brain waves while they performed the technique. The students’ EEGs indicated that theta and some alpha activity was present in the mid-region of their frontal lobes while practicing Su-soku (Figure 5), and that this activity was associated with changes in their heart rhythms, indicating a possible link to the nervous system changes that are sometimes seen during meditation (Section 1). An imaging study using fMRI also revealed activation of the frontal lobes in 11 Zazen meditators who engaged in Su-soku during the scanning session (Ritskes et al., 2003), further indicating the involvement of the frontal region in this technique.

 

Figure 5. EEG activity in student volunteers practicing Su-soku, showing theta activity, mixed in with some alpha, in the mid-region of their frontal lobes (upper right) (Kubota et al., 2001).

3.5. Vipassana (“Insight”) Meditation

So far, only a few studies have examined another sub-form of mindfulness meditation known as vipassana (“insight”), in which the meditator initially attends to their present thoughts or to an internal bodily process (usually their breathing), and then gradually broadens their attention outward to become passively aware of the range of internal and external stimuli present in their surroundings. In a sense, the meditator lets their attention freely wander about and observe various objects or processes, with the goal of gaining equanimity (see Table 1) and clarity in their awareness.

As a way to compare mindfulness with concentration meditation, psychologist Bruce Dunn and his associates at the University of West Florida had taught a group of 10 college students how to meditate using a concentrative technique (focusing on their breaths, similar to TM) and a mindfulness technique that closely resembles vipassana. After a little over a month of practice with each technique, the students were asked to meditate using each technique while their EEGs were recorded. Compared to concentrative meditation, the vipassana-like mindfulness meditation was associated with more brain wave activity in the delta, theta, alpha, and beta frequencies. The theta activity was localized primarily to the frontal lobes, while the delta, alpha, and beta activity was spread out more across the frontal, temporal, and parietal lobes. Curiously, many of these wave patterns appeared simultaneously in their respective brain regions. Dunn and his associates suggest that this may be consistent with the idea of meditation of being a state of “relaxed awareness”: slow brain waves (e.g., theta) appearing in the front of the brain may contribute to the meditator’s calming of their mind, while faster brain waves (e.g., alpha, beta) occurring in the back of the brain may at the same time keep the meditator alert and aware of their surroundings (Dunn et al., 1999).

To further explore the brain regions active during vipassana, German neuroscientist Dieter Vaitl and his associates at Justus-Liebig University had recruited 30 meditators with an average of 8 years of daily vipassana training and asked them to meditate on the breathing sensation in their nose while undergoing an fMRI scan. Compared to a control group of non-meditators, these advanced meditators showed more activity in the anterior cingulate cortex and the upper middle part of their frontal lobes (Hölzel et al., 2007).

 

 

Figure 6. An MRI comparison of the averaged brain activity of advanced meditators and non-meditators. Compared to the latter, the former showed more activity in the anterior cingulate cortex (large yellow area) and the upper part of the frontal lobes (small yellow area) (Hölzel et al., 2007).

 

4. Studies with Advanced Meditators

 

Given their long (five years or more) and often intense history of training, one might think that advanced meditators could be particularly revealing about what goes on inside the brain during the practice of meditation for two reasons. First, close examination of their brain structure and function might be able to tell us something about the long-term effects of such practice. Second, personal accounts of experiencing a “deep” or “higher” meditative state traditionally come from more advanced meditators (Section 1), and thus, they might offer some insight into the possible brain correlates of such states.

 

4.1. Tibetan Buddhists

 

One population of advanced meditators that could make valuable contributions to the study of the meditating brain is that of Tibetan Buddhist monks who have devoted a good part of their lives to the practice of meditation as part of their spiritual lifestyle. Often times this has been difficult, since many of the most accomplished monks have led reclusive lives in isolated Southeast Asian monasteries, but recently it has been possible to obtain the cooperation of several well-trained monks through the gracious assistance of His Holiness, the Dalai Lama (Barinaga, 2003; Knight, 2004). Some of the most interesting research with Buddhist monks so far has been conducted by psychologist Richard Davidson and radiologist Andrew Newberg.

 

Davidson and his colleagues at the University of Wisconsin have performed two studies in which they were able to examine the brain waves of two groups of long-practicing (6 years or more) monks during two separate forms of meditation. In one study (Lutz et al., 2004), eight monks had shown strong gamma wave patterns and signs of EEG coherence (Section 3.1) across their frontal and parietal lobes while engaging in a Tibetan meditative technique meant to produce an inner state of “benevolence and compassion” toward living beings.

 

In the other study (Brefczynski-Lewis et al., 2007), 14 monks focused their attention completely on a small dot on a computer screen during their practice of the “one-pointed concentration” meditation. While doing so, fMRI scans of their brains indicated several regions in their frontal and parietal lobes that became activated, all of which are thought to be involved in attention. In addition, the findings suggest that the more years of practice that the monks had, the less activation they showed. This in turn may suggest that the more practiced the monks are in focusing their attention during meditation, the less mental (and thus, brain) effort they have to exert in order to achieve a focused meditative state. Their continual practice may help them develop the ability to slip into such a state quickly and easily.

 

Newberg and his associates at the University of Pennsylvania Medical Center obtained SPECT scans from eight Tibetan Buddhists, each with more than 15 years of training, as they quietly focused on a mental image with gradually increasing intensity, with the goal of attaining “a sense of absorption into the visualized image associated with clarity of thought and a loss of the usual sense of space and time” (Newberg et al., 2001, p. 114). During their focus, increased blood flow was seen in their frontal lobes and the anterior cingulate cortex. In addition, an inverse relationship was found between the amount of blood flow in the frontal lobes and the amount in the superior parietal lobule such that as the flow in one region increased, the flow in the other decreased (and vice-versa) (Figure 7). These findings are notably similar to those that Newberg and his associates obtained in a separate SPECT study of Franciscan nuns practicing meditative prayer (Newberg et al., 2003; see also Section 3.3).

 

 

Figure 7. Averaged SPECT results from eight Tibetan Buddhists engaged in focused meditation. Compared to a resting baseline, increased blood flow was observed in the frontal lobes (left image), while a decrease was seen in the parietal lobes (right image) (Newberg et al., 2001).

 

Neuroscientist Dietrich Lehmann and his colleagues at the University Hospital of Zurich, Switzerland, had the opportunity to record the EEG of a Buddhist Lama who was able to voluntarily self-induce five meditative states, each of which he reported as a separate and profound experience. In the first two states, the Lama focused on a mental image of the Buddha appearing either in front of, or just above, him. During his visualization, a pattern of gamma waves appeared over areas in his occipital and parietal lobes that are involved in producing mental images. In the third state, the Lama concentrated on a mantra composed of 100 syllables by verbally reciting a list of words containing that many syllables. While he was reciting, gamma waves appeared over areas in his frontal and temporal lobes that have a role in speech. In the last two states, the Lama imagined his self transcending into a “boundless unity,” or “emptiness,” and then returning to his body. Once more, a pattern of gamma waves appeared, this time over regions in his frontal and parietal lobes that may be involved in self-perception and identification (Lehmann et al., 2001).

 

4.2. Transcendental Meditators

 

A second population that could make valuable contributions is that of advanced Transcendental Meditators who have closely studied under Maharishi Mahesh Yogi or those teachers that he had personally trained and qualified. Generally, EEG studies of advanced TM meditators have shown a trend towards slower brain waves in the alpha and theta range, similar to that seen in novice and intermediate meditators (Banquet, 1973; Cahn & Polich, 2006; Ferguson, 1975; Jevning et al., 1992; West, 1979, 1980; Woolfolk, 1975; see also Section 3.1), although in some cases this trend seems to have been marked by unique characteristics. For instance, French psychiatrist Jean-Paul Banquet (1973) noticed that as the brain wave patterns of 10 TM meditators slowed from alpha to theta, with the latter sometimes appearing as small “bursts” or “spikes” on the EEG record. These “theta bursts” were also later observed in the EEGs of 21 (27%) of the 78 long-term TM meditators studied by Swiss neuroscientists R. Hebert and D. Lehmann (1977) (Figure 8). These bursts occurred about every two minutes during the meditation, and, according to the meditators, they seem to be associated with peaceful and pleasant inner feelings of “drifting” or “sliding” (p. 401).

Figure 8. EEG activity recorded from an advanced Transcendental Meditator, showing brief “bursts” or “spikes” of theta activity mixed with in with alpha (Hebert & Lehmann, 1977).

Banquet (1973) further noticed that four TM meditators who reported achieving the deep meditative state of “transcendence” had suddenly shown a much faster 20 Hz beta wave pattern on their EEG. Similar beta wave patterns have apparently been observed in a few other meditators who have entered deep meditative states, as well (West, 1980). On a separate note, Canadian neuroscientist Michael Persinger (1984) found that when a female TM meditator with 10 years of training had reported experiencing a meaning state of transcendence in which “she had felt being very close to ‘the cosmic whole’” (p. 129), she had shown a brief “spike” pattern of very slow delta waves in her temporal lobe.

EEG coherence has also been noted in some advanced TM meditators. As briefly mentioned in Section 3.1, brain wave synchronization can be exhibited by novice and intermediate meditators, which in the early stages of TM can be in the form of synchronized alpha and theta waves occurring across various regions of the brain (Jevning et al., 1992, p. 419). In deep meditative states, a steady pattern of synchronized beta waves has been observed in early studies of advanced meditators, as well (Ferguson, 1975, pp. 22 – 25; see Figure 2). A more recent analysis of the EEGs of 16 meditators with nearly 10 years of TM training further revealed signs of alpha wave coherence occurring over their frontal lobes during meditation (Travis & Wallace, 1999).

The alpha activity occurring over the frontal lobes is consistent with the findings of the only imaging study done to date with TM meditators (Jevning et al., 1996). Compared to a group of non-meditating control volunteers, 18 meditators with 8 to 12 years of daily TM practice showed higher rates of cerebral blood flow over their frontal and occipital lobes.

 

4.3. Traditional Yogis

Traditional Indian Yogis comprise a third population of advanced meditators who may contribute valuable data on the meditating brain. As with Tibetan Buddhist monks, opportunities to locate accomplished Yogis who would be willing to participate in research have been limited because many of them have resided in mountainous retreats and other secluded, out-of-the-way places. One of the earliest came in 1957, when UCLA researchers Basu Bagchi and Marion Wenger had traveled to India in order to conduct explore the physiological aspects of Yogic meditation and exercise. Their journey took them to three Indian laboratories, two hermitages, and a cave dwelling high up in the Himalayas. Using a portable transistor polygraph, they were able to measure changes in the autonomic nervous system of five older Yogis as they sat perfectly still in the lotus position and meditated. Compared to a group of yoga students, the Yogis showed faster heart rates, higher blood pressure and skin conductance in their palms, and lower finger temperatures while meditating (Wenger & Bagchi, 1961, p. 315). Their breaths were also noted to become very slow and shallow, to the point where they would sometimes not be countable. The EEG recordings tended to show a steady alpha wave pattern throughout the meditation period, with little sign of any other change (Bagchi & Wenger, 1957). None of the Yogis reported reaching a deep meditative state during the monitoring sessions, however.

Indian physiologist B. K. Anand and his colleagues were able to independently follow-up on the work of Bagchi and Wenger a few years later in a study of four Yogis (Anand et al., 1961). Each of the Yogis was proficient in Raj Yoga, another type of Yoga meditation in which they reportedly become oblivious to any internal and external distractions in their surrounding environment while in the deeper state of mahanand (“ecstasy”). To explore this, Anand and his colleagues monitored the EEGs of the meditating Yogis while trying to externally stimulate them by flashing a bright light, making loud bangs, and lightly touching them with a hot glass tube. While in their ordinary waking state, each of the Yogis clearly responded to each of the stimulations. However, while meditating, they showed no response, either overtly or on their EEG. Consistent with Bagchi and Wenger’s (1957) finding, the four Yogis each showed a steady pattern of alpha waves, which was not interrupted by any of these stimulations.

Anand and his colleagues also studied two Yogis who had apparently developed a high tolerance for pain during meditation. To explore this, the researchers placed the Yogis’ hands in near-freezing (4ºC) water while they were meditating, and the Yogis were indeed able to keep their hands immersed for nearly an hour without experiencing any signs of discomfort. As with the other four Yogis, steady alpha activity was observed on their EEGs throughout the immersion period. No EEG signals were seen in their parietal lobes, which handle sensory information coming from the body, suggesting that they indeed were showing no signs of a response to the ice-cold water (Anand et al., 1961).

In the 1980s, a field study was made of a group of Buddhist monks who practice an advanced type of Yoga meditation known as g Tum-mo, which ostensibly allows the meditator to produce notable rises in their body temperature, even in the cold climate of the Himalayan foothills.⁶ As a way to informally demonstrate the heating effect of g Tum-mo, the bare bodies of the monks are each wrapped in a sheet that has been soaked in ice-cold water, and their goal is to fully dry the sheet using only the heat that is generated within their body during the meditation. Within 3 to 5 minutes of beginning their meditation, the monks have reportedly been able to heat the sheets enough to make them give off steam, and after about 45 minutes, the sheets were completely dried. The monks reportedly do not shiver throughout the process despite the exposure to the wet sheets and often cold atmosphere of the mountainous monastery.

With help from the Dalai Lama, Harvard psychiatrist Herbert Benson and his associates were able to visit three Buddhist monks in India who had practiced g Tum-mo for more than 6 years to conduct a more formal exploration of the heating phenomenon. As the monks meditated, Benson and his associates measured the skin temperature at various points on their bodies. These measurements indicated that the monks were able to increase the temperature in their fingers and toes by as much as 8ºC while meditating, even while still maintaining a fairly normal heart rate (Benson et al., 1982). EEG measurements that Benson and his associates collected during a follow-up study of three other monks showed increases in beta wave activity during g Tum-mo meditation (Benson et al., 1990).

Aside from field work, laboratory studies of advanced Yoga meditators have provided useful insight. In addition to novice and intermediate meditators, the two studies of Tantric Yoga summarized in Section 3.2 also examined the brain wave activity of a small number of advanced Yoga meditators. In the first study (Corby et al., 1977), EEG data were collected from a Yogic monk and teacher who had received just over two years of special advanced training. Whereas a majority of the novice meditators spent between 4 and 32% of their time in a meditative state that was marked by the presence of theta waves, the monk had spent 86% of his time in this state, suggesting that he was more adept at producing these slower brain waves. This theta pattern persisted on the monk’s EEG even after he had stopped meditating and had opened his eyes, something not seen in any of the novice meditators.

Similarly, the advanced meditators participating in the second study had shown higher amounts of theta activity than intermediate meditators (Corby et al., 1978). All of them had visited India to meet the leader of their spiritual organization, and had received the most advanced set of meditation techniques. While focusing on a mantra, one of these advanced meditators had reportedly experienced a “near-Samadhi” state in which she had the feeling of “having my breathing taken over by the mantra” (p. 574). During that experience, her breathing, heart rate, and electrical skin resistance had sharply increased. While no clear EEG changes occurred during her experience, her meditation period was marked by alpha activity and large amounts of theta waves that occasionally came in small “bursts,” similar to that seen in TM meditators (Section 4.2).

Researchers at San Francisco State University conducted a physiological study of a Japanese Yogi who was highly proficient in the practice of Kundalini Yoga, as indicated by his bestowed title of Yoga Samrat from the Indian Yoga Culture Federation. While meditating on a massage table in a position similar to the half-lotus, the Yogi showed a sharp drop in his breathing rate to only 5 breaths per minute. Alpha activity increased on his EEG during his meditation, and was followed afterward by an increase in theta waves (Arambula et al., 2001).

Neurologist R. Murali Krishna (2005) recently reported an exploratory study with an Indian Swami and teacher of Nithya Yoga during a visit to his clinic in Oklahoma. PET scans of the Swami’s brain during meditation revealed increased metabolic activity in the forward parts of his frontal lobe. As the Swami reported the experience of “opening his Third Eye,” the lower central region of his frontal lobe lit up with activity. In addition, EEG monitoring indicated that the Swami was able to voluntarily make a continuous transition between the various types of brain waves during deep meditation, suggesting that his brain was capable of voluntarily shifting between brain waves and their associated mental states.

 

4.4. Zen Meditators

As with Indian Yogis, opportunities to obtain valuable data on the meditating brain from Zen Buddhist monks can be traced to an early history, largely due to the efforts of local researchers. In the mid-1960s, Japanese researchers Akira Kasamatsu and Tomio Hirai (1966) were able to record the meditating EEGs of 16 Zen priests and 32 of their disciples during a period of Sesshin. Whereas the disciples had a tendency to show steady alpha waves even with their eyes open (Section 3.2), the priests tended to exhibit further progression of their EEG activity. A few minutes after beginning Zazen, the priests would show the alpha patterns over the frontal lobes typically seen in the disciples. However, after about 30 minutes, this alpha pattern would gradually slow down into a rhythmic pattern of theta waves. About 20 seconds later, this theta pattern would take the form of short “bursts” or “spikes,” similar to that seen in the EEGs of some TM and Yoga meditators (Sections 4.2 & 4.3). At the end of the Zazen period, a return to the alpha pattern was seen, which persisted for several minutes afterward.

In line with this observation, the data gathered by Kasamatsu and Hirai (1966) suggest that the appearance of the theta pattern is related to the amount of Zazen training that the meditator has had, with the pattern appearing largely in meditators with more than 20 years of training. Findings from later EEG studies of Zazen further supported this relation (Chiesa, 2009, p. 587, Ivanovski & Malhi, 2007, pp. 84 – 87; Woolfolk, 1975, p. 1330), suggesting that these progressive EEG changes may be the fruits of regular long-term practice.

A group of Danish psychologists was recently able to examine the activity in the brain at the beginning of Zen meditation in an fMRI study with five meditators who had between 7 and 23 years of training (Bærentsen et al., 2001). The fMRI scans revealed that, at the onset of their meditation, the meditator’s brains were increasingly active in the left side of the frontal lobe, the right parietal and temporal lobes, and the anterior cingulate cortex. In contrast, a decrease in activity was seen in the visual regions of the occipital lobe.

4.5. Vipassana Meditators

Recent studies of advanced vipassana meditators have made a preliminary effort in exploring another aspect of the meditating brain: the possible effects that regular practice in meditation may have on the structure and function of the brain, which we might call “training effects.”

The possibility that even a short period of regular practice in meditation may produce functional changes in the brain was initially explored in a study by psychologist Richard Davidson and his associates at the University of Wisconsin, in which they recorded the EEGs of volunteers at a corporate firm both before and after they received an 8-week training program in a simple form of mindfulness meditation designed to help reduce stress. Compared to before the program, the volunteers showed more alpha activity in the left central region of their brain after the relatively short program. A group of control volunteers who did not take the training program showed little to no such signs of alpha increase. The program volunteers also reported having less anxiety and fewer negative feelings than the control volunteers (Davidson et al., 2004).

More long-term effects of meditation practice were explored in an imaging study conducted by a team of researchers from Massachusetts General Hospital, Harvard Medical School, Yale University, and MIT, led by psychiatrist Sara Lazar. They recruited 20 meditators who had an average of 9 years of training in vipassana and measured the thickness of the neural tissue in their cerebral cortex using an advanced form of MRI. Compared to a group of non-meditating control volunteers, the meditators showed indications of thicker tissue in cortical regions that have been found to be active during meditation, including central regions of the frontal lobe, as well as an area between the frontal and temporal lobes known as the insula, which is involved in the perception of internal bodily responses (Lazar et al., 2005). In most cases, the thickness of our brain’s cerebral cortex tends to get thinner with age. These findings suggest that meditation may help slow this process in cortical areas around the frontal lobe, a potential health benefit.

Neuroscientist Dieter Vaitl and his associates at Justus-Liebig University in Germany extended the findings of Lazar’s team by using MRI to measure the masses of neural cell tissue that comprise the cerebral cortex, known as gray matter.⁷ Compared to non-meditating control volunteers, 20 meditators who had an average of 8.6 years of vipassana training showed greater concentrations of gray matter near the insula, the hippocampus, and the left temporal lobe (Hölzel et al., 2008).

Using the same MRI technique, a team of neurologists at the UCLA School of Medicine recently made a further attempt to extend these findings to a wider variety of meditators. Scanning the brains of 22 meditators who had an average of 24 years of training in vipassana, Zazen, Yoga, and other forms of meditation, the team found larger volumes of gray matter in the hippocampus, the left temporal lobe, and the lower part of the frontal lobe (Luders et al., 2009).

These results suggest that certain areas regularly active in the brains of long-term meditators may structurally alter themselves over time, such that the masses of tissue around these regions slightly thickens, or begins to concentrate more in these areas, perhaps due to greater neural cell proliferation in those areas.

 

5. Discussion

The experimental findings reviewed here tentatively suggest that the meditative state may induce short-term changes in brain activity that are in line with the dual views of meditation as a technique of relaxation, and as a technique of mental cultivation. Although their individual techniques and philosophies somewhat differ, the various forms of meditation that we have looked at here seem to share the basic commonality of being able to gradually induce a calmer state of mind, based on EEG monitoring. As one enters a meditative state, brain wave activity begins to slow and ease into frequencies in the alpha and theta range, frequencies commonly associated with relaxation and low arousal. In some cases, these alpha and theta patterns may briefly linger even after one has slipped out of the meditative state and returned to the normal waking state, a unique ability not often seen in the EEGs of non-meditators.

The mental cultivation aspect is perhaps best reflected by advanced meditators in their ability to frequently produce and maintain steady alpha and theta rhythms, to achieve EEG coherence, and, in the case of Buddhist monks, to enter the meditative state with relatively little mental effort. These feats seem to suggest that, through continual training of their attention and awareness, these individuals have been able to gradually develop and refine their mental and brain processes to a point where they are capable of operating more coherently, and are under greater voluntary control. Such a capacity would be consistent with the traditional perspectives on meditation expressed in Buddhism and Taoism⁸, which emphasize mental development in order to encourage beneficial thought processes (calmness and concentration) and positive emotions (love and joy), and reduce negative ones, such as fear and anger (Goleman, 1988; Walsh & Shapiro, 2006).

The possibility that one’s attention is harnessed and developed during meditation may be supported by the finding that several forms of meditation engage cortical regions that may be part of a network of brain areas involved in attention, such as the frontal lobes (Frith et al., 1991; Ingvar, 1994; Pardo et al., 1991) and the anterior cingulate cortex (Devinsky et al., 1995; Posner & Dehaene, 1994; Posner & Petersen, 1990). Some studies suggest that the anterior cingulate cortex is also involved in the regulation of some functions of the autonomic nervous system (Devinsky et al., 1995), which may tie in to the changes in breathing, heartrate, and electrical skin resistance that are sometimes observed in meditators. The regular engagement of the frontal lobe may promote neural activity and proliferation in that region, and thereby work against age-related thinning of its cortical tissue, as suggested by the training effects observed in vipassana meditators (Section 4.5). Though gradual over time, such effects would likely serve as a health benefit of regular meditative practice.

Regular practice may also bring about training-related changes in the grey matter of the cerebral cortex, suggesting that there is some degree of flexibility in the way our brains are structured. It is interesting to note that similar training effects on grey matter have been observed in the brains of people who are just learning a new skill, such as how to juggle (Draganski et al., 2004). If these findings are valid, then they may indicate that it is possible to, in a sense, “re-structure” the brain through persistent practice so that it adapts to function more effectively in performing a complex skill, adding new meaning to the old adage that “practice makes perfect.”

The role of the theta rhythm may also be relevant to the issue of which brain areas are activated in meditation. Although it is most often associated with low arousal and light sleep, there is now some evidence to suggest that theta activity occurring around the frontal and midline regions of the brain can sometimes be associated with attention and mental concentration (Inanaga, 1998; Klimesch, 1999). One study has produced findings to indicate that this kind of theta rhythm may be reflective of alternating activity between the frontal lobes and the anterior cingulate cortex (Asada et al., 1999), providing a possible key link between meditation, theta waves, and these two brain regions. This may be only one part of the equation, however; it seems that meditation may be a complex mental process involving several other components of the autonomic nervous system and the brain, including the hippocampus, the amygdala, and various parts of the brainstem (Newberg & Iversen, 2003).

On a separate note, the experimental findings with advanced meditators offer us a bit of insight into the possible brain correlates of deep or higher meditative states, insight that may be valuable in the quest to develop an answer to the problem of how neural processes in our brain give rise to conscious experience, the so-called “hard problem” of consciousness (Chalmers, 1995). One might argue that in order for us to gain a better understanding of consciousness in general, we must be able to consider all forms of it, including deep meditative states.

EEG observations of TM meditators and Buddhist monks seem to indicate that as one enters a deep meditative state, brain wave activity tends to speed up rather than slow down, approaching frequencies in the beta and gamma range. These frequencies are usually associated with heightened alertness and complex cognitive thought processes, suggesting that a form of “focused arousal” might characterize these states.

In contrast, observations of Yoga and Zen meditators seem to indicate that deep states occurring in these practices are more often marked by constant alpha and theta patterns, which are suggestive of a state maintained at the boundary between wakefulness and the early stages of sleep. This boundary state, often called a hypnagogic state, can be characterized by intense dream-like images that occur as one is falling asleep. The steady presence of alpha and theta could mean that Yoga and Zen meditators are capable of inducing and maintaining a hypnagogic state while still remaining awake. If that is so, then perhaps the images produced during such a state comprise part of a deep Yogic or Zen meditative state. Alternatively, constant theta activity focused over the frontal and midline regions may reflect a state of deep attentional focus or concentration, as noted above. For now, these ideas remain speculative, and it is hoped that further EEG research with meditators capable of entering deep states will shed more light on this interesting and important aspect of consciousness.

 

6. Conclusion

Based on our review of the experimental findings, both past and present, what lessons might we be able to take away about the meditating brain? The first lesson may be a practical one for our health: Aside from calming our minds, the findings tentatively suggest that the practice of meditation may help slow the thinning of cortical tissue in our frontal regions that naturally occurs with age. If this is a genuine effect, then it seems to be associated with regular, long-term practice, so it may be useful to have a daily period of meditation as part of one’s health regimen. Thus, if you practice meditation on a regular basis, it may be beneficial in the long run to keep it up!

Another lesson we might be able to take away is one about deep meditative states. The limited research with advanced meditators suggests that these states, which tend to be subjectively different from the ordinary waking state of consciousness, may have a partial basis in activity at both ends of the brain wave frequency spectrum. Some deep states appear to be linked with slow frequencies associated with deep relaxation, low arousal, and the waking-sleep threshold, while others are associated with fast frequencies associated with complex cognitive thought processes. Due to the paucity of the research, there is little we can conclude at the moment, but with further work, what we learn about them can be potentially valuable for gaining a better understanding of the boundaries of consciousness that lie at the edge of the hard problem.

Lastly, we might be able to take away a lesson about cultural approaches to the human mind. For about 2,500 years, Buddhism has offered a spiritual means of personally exploring the inner self and contemplating the nature of the mind using techniques of deep introspection. At its heart, Western psychology shares this same focus of exploration and contemplation using empirical techniques. Even though they may take different perspectives, psychologists Roger Walsh and Shauna Shapiro (2006) have argued that there is much that the two disciplines can learn from each other. For example, the findings from psychology and neuroscience can aid Buddhists in more deeply exploring their first-person insights and mental states, while Buddhists can offer psychology and neuroscience a broader perspective on introspection and subjective experience, two things that are vital in linking the workings of the brain to mental behavior (Barinaga, 2003). The study of meditation is one way that this path of knowledge can be facilitated.

Upon accepting the Nobel Peace Prize in 1989, His Holiness the Dalai Lama once stated: “Both science and the teachings of the Buddha tell us of the fundamental unity of all things” (Knight, 2004, p. 670). If a mutual consideration of these two disciplines can lead to a unity of knowledge and perspective, it might just lead to a greater advancement in our quest to better understand the human mind.

 

Notes

 

1. It should be noted that although many studies point toward a beneficial effect, the consistency of their findings is limited by their experimental design, methods, and variety of meditative techniques explored (Ospina et al., 2008). While these have been improving with time, it is wise to view these findings as “tentative” at the present, with further direction to be offered by future research.

 

2. One issue that has been raised is whether the calming effects of meditation are any different from the calmness that can be achieved through simple rest. To explore this issue, University of Kansas psychologist David Holmes (1984) reviewed the research comparing rest with meditation (the latter being TM in most cases). Based on a simple “vote-counting” comparison, he found little difference between them with regards to physiological processes such as heartrate, skin resistance, and blood plasma changes. (Because of its calming effects, one would expect meditation to show sharper decreases in these processes than rest.) However, a closer statistical evaluation of the research by TM researchers Michael Dillbeck and David Orme-Johnson (1987) found significantly more decreases in these processes in meditators than in resting control volunteers. Thus, there may be some indication that meditation is different from simple rest, although this finding should be considered tentative, as well (see Note 1).

 

3. A classic example of a koan that is likely to be familiar to many is the falling tree riddle: “If a tree falls in a forest and no one is there to witness it, does it make a sound?”

 

4. This is notable because alpha activity is usually much more prevalent when the eyes are closed rather than open (Carlson, 1992, p. 242; Kolb & Whishaw, 1990, p. 53).

 

5. Practicing Su-soku is meant to help the initiate gain proficiency in the ability to keep attention focused on a specific object or thought, as doing so will be necessary in order for them to continually focus on a koan during Zazen (Woolfolk, 1975, p. 1330). This is one example of how techniques from the two classes of meditation (concentration and mindfulness) can be blended, as mentioned in Section 1.

 

6. According to the traditional philosophy underlying g Tum-mo, prāna (literally meaning “wind” or “air”) is collectively extracted from the scattered, random fluctuations of normal conscious experience and channeled into the body’s “central channel.” As prāna dissolves within this central channel, it builds up the “internal heat” that creates the rises in body temperature. From this perspective, the heating effect follows from a spiritual energy practice (Benson et al., 1982, p. 234).

 

7. As one might surmise, the term “gray matter” refers to the appearance of the neural cell tissue, based on the grayish brown color of the individual cell bodies that make up the tissue. This is in contrast to the other type of neural tissue mass found in the brain, known as “white matter” due to the pale color of the fatty substance that surrounds the outer branches of nerve cells in order to insulate them (Kolb & Whishaw, 1990, p. 6).

 

8. For instance, the term bhavana (mental cultivation) is used in the Buddhist tradition, while the term lien-hsin (refining the mind) is used in the Taoist tradition (Walsh & Shapiro, 2006, p. 228).

 

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