The meditating brain

A small but growing field of research at the junctions between biology, psychology and medicine focuses on what happens in the brain during meditation.

Scientists in a number of countries are exploring how the brain meditates and conveys a relaxation response to the body. The picture is still fragmented, but taken together the results indicate that certain brain areas such as the prefrontal cortex are instrumental in instigating the physiological processes that take place during meditation. In this article we will have a closer look at this fast-moving field of meditation research.

At a biological level, all our conscious experiences take place in the outer layer of the brain, called the cortex. During the last few years, several research groups have explored which areas of the cortex show increased activity during meditation. The prefrontal cortex and associated areas seem to be the most active.

Prefrontal cortex: advanced consciousness

These observations tell us something about what kind of mental activity meditation is. The prefrontal cortex may be regarded as the location of our most advanced consciousness concerning ourselves and our surroundings. Unlike brain areas for vision, hearing, touch, muscular control, etc., it does not receive information directly from our sensory apparatus and does not directly control bodily functions. Instead, it brings together pieces of information from many areas of the brain, creates an understanding of these and gives guidelines or directions back to subordinate areas. Meditation, therefore, seems to be a higher-level process in which the brain influences body functions, triggers relaxation and perhaps also influences our understanding of ourselves and our surroundings. The findings also suggest that meditation is not a passive, trance-like state, but an active process of discrimination that may play a role in modifying activity patterns in other parts of the brain.

Another possible implication is that during meditation, perception and action are closely interrelated. In simple terms, two important and well-known types of cortical area are the receiving (sensory) areas, which are allocated to sensory perception, and executive (motor) areas, which control bodily functions. Both are connected to the body and the world around us, either by receiving sensory information, or by talking back through different types of motor nerve cells. But the prefrontal cortex does not distinguish as clearly between receiving and executive areas as many other parts of the cortex, such as the areas that receive information from touch sensation and those that send information back to the muscles in the same part of the body.

Let us now review scientific studies to date that have attempted to advance our understanding of meditation from a neurobiological perspective.

Alpha waves: relaxed wakefulness

In the 1960s, scientists in Japan, India and America began to study electrical activity in the brain during meditation, most often Zen meditation and transcendental meditation. In Acem’s terminology, these are nondirected meditation techniques, performed without effort or concentration. The researchers placed electrodes upon the experimental subjects’ scalps and connected these through wires to an amplifier and a voltage meter. This technique, known as electroencephalogram or EEG, makes it possible to record the combined electrical activity in thousands of cortical nerve cells

EEG is a method for recording electrical activity of groups of nerve cells in the brain cortex. The recorded brain waves are classified according to five levels of increasing frequency, each of which is typical of certain kinds of mental activity:

• delta: deep sleep, coma

• theta: some sleep states, states of quiet focus, meditation

• alpha: relaxed wakefulness, meditation

• beta: active, busy thinking, active concentration

• gamma: active exchange of information between different brain areas, conscious waking states, meditation that are signalling in phase, i.e. emitting their signals simultaneously according to the same rhythmical pattern. The rhythmic oscillations seen through these recordings are of five different types. These are normal patterns of brain activity, reflecting distinct functions like sleep, rest, demanding cognitive tasks, etc.

In an early study by Robert Wallace at the Center for Health Services in Los Angeles, published in the journal Science in 1970, the cortex displayed regular alpha activity during meditation. This is typical of relaxed wakefulness with closed eyes. Both the regularity and the amplitude of the alpha waves increased during meditation compared to non-meditative rest. In some instances, however, the alpha waves would slow down and even stop for a few minutes, while theta waves predominated. This pattern differed from normal rest, which only has alpha waves, and sleep, which typically has the much slower delta waves. It is also different from cognitive tasks such as mathematical problem-solving that demand high levels of concentration, during which alpha-wave amplitude is reduced.

A number of similar studies were published during the years that followed. However, there is not yet any consensus concerning the existence of a distinctive pattern of electrical brain activity during meditation. One reason may be that the researchers have studied different meditation methods, not all of them nondirected. Another may relate to weaknesses in experimental design. A third may be that meditation is not a static phenomenon; the neurophysiological qualities may change from one meditation session to another and even within a single session.

Still, it seems safe to conclude that brain activity during meditation is different from both sleep and demanding cognitive tasks like mathematics. Some people regard the increase in alpha-wave activity during meditation as a sign of a completely different mental state, but science does not support this interpretation. On the contrary, alpha waves are very common, constituting the dominant pattern when anyone sits quietly with closed eyes while awake. They are not specific to meditation, although their increased regularity and amplitude during meditation seems to be different from ordinary rest.

Theta waves: slower heart beats

A Japanese team of researchers, led by Yasutaka Kubota at Kyoto University (Cognitive Brain Research 2001), combined EEG with electrocardiogram recordings (ECG, monitoring the electrical activity of the heart) to investigate whether and how the brain modulates heart activity during meditation. Their starting point was the observation, made by Wallace and subsequent researchers, that meditation may elicit theta-wave activity in the brain, close to the midline in the frontal lobe (of which the prefrontal cortex is a part). Others have documented that alleviation of anxiety also may elicit theta-wave activity in this brain area.

The Japanese researchers recruited 25 students who had not previously practised meditation. They were asked to count every breath with a regular rhythm, a practice known within Zen as “su-soku”. The kind of attention employed during this exercise was characterised as “sustained concentration”. The investigators performed both EEG recordings of the brain and ECG recordings of the heart in students practising su-soku. Theta activity in the frontal midline was induced in 12 of the 25 students. These subjects were selected for further EEG and ECG profiling.

During periods with strong theta-wave activity, the students showed a slightly decreased heartbeat frequency, exactly the opposite of what normally happens when performing demanding mental operations. The results suggested a close connection between activity in the frontal midline of the brain and autonomic regulation of heart activity. Theta-wave activity in the frontal area typically came in periods where there was little activation of the sympathetic nervous system, the part of the nervous system that is activated during stress.

This study shows that meditation may induce theta-wave activity in areas near the frontal midline of the brain, and this specific brain activity may also influence the pattern of activity in the heart. Thus, there is a link between brain activity during meditation and the function of the heart. The specific change in heart activity is not the focus of Kubota’s study, and has been investigated more thoroughly by others. What this study seems to show, however, is that meditationrelated brain activity may initiate changes in the heart’s activity pattern.

The authors go one step further in their interpretations. They point to other studies showing that theta-wave activity in the frontal midline of the brain during intensive mental tasks has its precise origin in an area of the cortex called the anterior cingulate cortex, or the ACC. It is likely that the ACC is the origin of the theta waves during meditation as well. The ACC is known to be involved in the maintenance of sustained attention, as well as in regulating autonomic functions like heart activity (probably through signals to the hypothalamus).

During debriefing, the student participants in Kubota’s study reported that they became quite immersed in their mental task of counting their breathing, and felt relaxed, rather than stressed, as when solving a demanding task. The researchers interpret the observation as follows: “…with an appropriate level of mental concentration for task performance, bodily relaxation also occurs. This specific state at the periods of frontal midline theta appearance during task performance can be called ‘relaxed concentration’.”

Gamma waves: improved brain function

Among the most highly ranked meditation studies of recent years is the one led by Antoine Lutz and Richard Davidson at the University of Wisconsin at Madison, on the EEG patterns of experienced practitioners of Buddhist meditation from the Nyingmapa and Kagyupa traditions. The results of this study were published in the Proceedings of the National Academy of Sciences, 2004. Each of the eight subjects had from 10,000 to 50,000 hours of meditation practice behind them, consisting of daily meditations and retreats averaging eight hours’ meditation per day. During the experimental meditation sessions, the participants were asked to generate a general state of “loving-kindness and compassion”, without reference to distinct persons. The EEG patterns of these experienced practitioners, both before and during meditation, were compared with those of ten control subjects who had learned meditation one week before.

Unlike most previous studies, this one focused on the effect of meditation on very rapid, high-frequency gamma waves, much faster than the alpha waves described above. The strength of these waves increased significantly at the start of meditation, then increased further during the first minutes of a meditation session. Comparable findings had not previously been described. In addition, some of Lutz and Davidson’s observations may indicate increased coordination between brain regions with different functions. Such coordination may possibly underlie certain forms of learning.

Both these observations are compatible with large numbers of cortical nerve cells, coordinating their signalling activity and working in phase. Transient networks between nerve cells are established, and this facilitates the integration of what goes on in different parts of the cortex, forming the basis for highly ordered cognitive and emotional mental processes. Other investigations have previously shown that synchronisation of gamma waves is important for attention, working memory, learning and conscious perception. In cells, synchronisation probably contributes to a change in the strength of connections between nerve cells.

One possible interpretation may be that the observed processes enable us to select something in our field of inner attention, against a background of more irrelevant activity. The selected activity is temporarily placed in our working memory, while associative links are formed that may still be active later on. The researchers conclude their study by stating that it is “consistent with the idea that attention and affective processes, which gamma-band EEG synchronization may reflect, are flexible skills that can be trained”.

The described EEG patterns are not unique to meditation, but the gamma activity in some of the practitioners is of a higher amplitude than any other recorded in the literature in a nonpathological context. The strength of gammawave activity was most pronounced in the subjects who had accumulated most meditation time (i.e., 50,000 hours). Lutz and Richardson also found that even before the meditation sessions started, there was a significant difference between beginners and advanced meditators, suggesting that the long-term effects of meditation are evident in normal everyday life.

Attentional-blink deficit: brain plasticity

Recently, the same research group has published another study about improving brain function by meditation (Slagter et al., PLOS Biology, 2007). In a rapid stream of events, when two stimuli follow each other closely in time, the second of the two is often not noticed. This is called the attentionalblink deficit. A widely held interpretation is that the two stimuli compete for limited attentional resources. The researchers show that three months of intensive training in Vipassana meditation may reduce this attentional-blink deficit. In this meditation technique, practitioners start by focusing or stabilising their concentration on an object, such as the breath. They subsequently broaden their focus, “cultivating a non-reactive form of sensory awareness”, in which they seek to avoid being caught up in judgements and affective responses about sensory or mental stimuli. The meditators are believed to regulate their attention in such a way that they allocate less of their brain resources to the first of the two stimuli, thus allowing more attention to be directed to the second stimulus. The authors conclude that mental training, in the form of meditation, may increase our control over the distribution of limited brain resources, with lifelong benefits for plasticity of the brain.

Left prefrontal cortex: positive mood changes

For many years, Richard Davidson has studied brain activity during different emotional states. Through EEG studies, he has found that stress-related emotions such as anxiety, anger and depression produce a predominance of activity in the right prefrontal cortex, while “positive affect”, like happiness and enthusiasm, causes the left prefrontal cortex to predominate. The predominance of one or the other side of the prefrontal cortex in any given individual is usually quite stable. For instance, one year after major and disturbing life events, such as paralysis due to a traffic accident, the original balance between right and left prefrontal cortex is restored. Thus, our emotional profile is quite consistent throughout our lifecourse.

In an article published in the journal Psychosomatic Medicine in 2003, Davidson and his co-workers reported research on participants in an eight-week training programme in mindfulness meditation, where meditators direct their attention towards spontaneously arising thoughts. They found that such meditation may result in increased left-sided anterior activation of the kind that is usually associated with reductions in anxiety and negative affect and increases in positive affect, as scored with psychological tests. This change in profile was still present four months after the end of the training programme.

The same study also evaluated another aspect of stressrelated biology. The immune systems of subjects in the meditation group reacted significantly more strongly (through higher antibody production) to an influenza vaccine than did the immune systems of members of the control group, an effect that is compatible with a lower stress level. Furthermore, the degree of left-sided prefrontal activity increase largely predicted the magnitude of the antibody increase in response to the vaccine. It will be interesting to see whether future studies confirm these results, and how the psychological and biological mechanisms behind the changes may be explained.

Brain imaging: prefrontal cortex and the ACC

EEG is an excellent method for detecting rapid activity changes in large groups of nerve cells in the cortex, but is less suitable for accurate localisation of ongoing brain activity. More recently developed techniques are better able to visualise differences in the intensity of brain activity between brain regions, some of them with high spatial resolution. Such techniques are collectively called “brain imaging”. Brain-imaging techniques can record and visualise distinct patterns of brain activity associated with anything from flexing a finger to emotions such as fear, moral dilemmas, unconscious psychological defence mechanisms, and the differences between love and sexual attraction. We are now seeing a growing number of studies using modern brain-imaging techniques on meditation.

One of the first such studies on meditation was conducted by Andrew Newberg and his co-workers at the University of Pennsylvania Medical Center in the USA and published in Psychiatry Research: Neuroimaging Section, 2001. In the laboratory, eight very experienced practitioners undertook more than two hours’ Tibetan Buddhist meditation in which attention is focused on a mentally generated image. When the meditation was at its most intense, the meditators gave a hand signal and the researchers started brain scanning.

The scanning technology used in this study was SPECT. A disadvantage of this technique is that the temporal and spatial resolution are not of the highest standard, though the spatial resolution is better than with EEG. Its main advantage is that it does not disturb the meditators, whose only unfamiliar sensation may be that of a canula slowly infusing contrast liquid into their veins. Other scanning technologies are much less appropriate for meditation research, for instance because they use very noisy machinery.

The study showed how the blood flow through different brain areas changed during meditation. Increased blood flow represents increased nerve-cell activity, while reduced blood flow signifies less nerve-cell activity. The researchers investigated 15 specific brain areas. Their main finding was that increased cortical activity is seen in the anterior, frontal part of the brain, including the prefrontal cortex. Another frontal area with increased activity during meditation was the ACC (see details of Kubota’s study, above). Newberg and his co-workers speculate that the increased activity in frontal cortical regions observed in their study is typical of active forms of meditation involving focused attention.

They contrast this with reports of meditation techniques that involve listening passively to recorded instructions. They point to the fact that among the four extant brain-imaging studies at that time, three show increased activity in the prefrontal cortex, while in the only study that showed reduced activity in this region, meditation was performed as a bodily relaxation exercise, led by verbal instructions from a tape recording. These authors do not distinguish between different types of attention or concentration, as in the Kubota study or in Acem Meditation.

Newberg and his team also noted changes in activity in other brain regions, such as in the rest of the cingulate cortex, or in deeper brain areas like the thalamus and the mesencephalon, though they can only guess at the functional significance of these observations. Other, similar studies have also reported activation patterns for which we still have no satisfactory functional explanations. For instance, Sara Lazar and co-workers at Harvard Medical School (Neuroreport 2000) found no less than nine cortical areas with increased activity during meditation (Kundalini meditation with repetition of different mantras during inhalation and exhalation), but could not explain this behaviour.

Several studies also point to activity in midline regions of the cortex, specifically in the ACC. Here too the activity may reflect the kind of attention used during meditation. As indicated above, this is an area known to be involved in the regulation of autonomic bodily functions such as heartbeat and breathing. These parameters are central in the relaxation response typical of meditation. Later studies seem to confirm the typical prefrontal activation during meditation. A recent paper by Britta Hölzel and co-workers at the Justus-Liebig-University in Germany (Neuroscience Letters 2007) replicates the main finding of increased activity in the prefrontal cortex and the ACC by means of fMRI scanning during meditation. The quality of this study was increased by the relatively large number of participants – 15 advanced meditators and 15 matched control subjects – and the level of detail in which the observed mental activity was described. Both groups performed Vipassana meditation, with attention focused on breathing sensations, and a control task in mental arithmetic. The brain scans revealed increased activity in subregions of the prefrontal cortex and in the ACC during meditation compared to what was observed in the subjects while they performed arithmetic. According to the authors, the prefrontal activation may indicate intensive engagement in emotional processing, while the ACC activity may reflect stronger processing of distracting events.

Summary

The main points of this article can be summarised as follows:

• Results vary between different studies and different meditation techniques, but a sizeable body of evidence supports the view that meditation is characterised by regular, large alpha waves similar to those observed during relaxed wakefulness with closed eyes. Some studies indicate increased alpha-wave regularity and amplitude in meditation as compared to ordinary rest.

• Meditation can instigate increased synchronisation of high-frequency gamma waves in the cortex. The functional significance of this phenomenon has not been firmly established, but one interpretation may be that the prefrontal cortex creates transient networks with other areas in the cortex, facilitating integration into highly ordered cognitive and affective mental processes, and forming the basis for aspects of learning. Possibly, what we see is the neurobiological basis for the way meditation helps to modify the individual’s established patterns of perception and action.

• At irregular intervals, brief periods of low-frequency theta waves appear during meditation. Such theta-wave activity in the frontal midline brain regions probably originates from the ACC (anterior cingulate cortex) and underlies the autonomic, bodily relaxation that is well documented during meditation, e.g. reduction in heart rate. This frontal midline theta-wave activity may be restricted to types of meditation that are practised with some degree of relaxed mental attitude, such as the ‘relaxed concentration’ of su-soku or the free mental attitude of Acem Meditation.

• One meditation study points to increased basal activity in the left prefrontal cortex, relative to the right prefrontal cortex. This tendency correlates with a reduced level of trait anxiety and also with a better-functioning immune system.

• Modern brain-scanning techniques like fMRI or SPECT have been used to characterise local and regional changes during meditation. By and large, these methods seem to confirm that the prefrontal cortex and the ACC are crucial brain areas during meditation. The former is generally involved in such higher-order functions as attention, cognitive understanding, executive control and short-term memory, while the latter conveys relaxation processes to the autonomic nervous system.