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Meditation and its effect on the central nervous system has become a budding collaborative research focus of neuroscience, psychology, and neurobiology over the past decade. Recent research on meditation in these fields have sought to both define and characterize various kinds of practices that can be considered meditation. This article focuses on presenting the anatomical and physiological changes in the brain associated with meditation backed by published literature.

Mindfulness meditation, most closely associated with Buddhist meditation practices, is the most heavily studied form of meditation. Notable practitioner and researcher of mindfulness, Jon Kabat-Zinn, describes mindfulness meditation as the complete, and unbiased attention on the current moment. Kabat-Zinn founded the Mindfulness-Based Stress Reduction program at the University of Massachusetts School of Medicine in 1979 which centers on using mindfulness meditation as a therapy for treating stress. Mindfulness meditation is considered to be a large component of Zen and Vipassana practices, both ancient forms of meditation.

Meditation’s effect on the brain can be broken up into two categories: state changes and trait changes. “State changes” will be considered as alterations in brain activities during the act of meditating, alternatively, “trait changes” will be considered as the changes that occur from the continual practice of meditation.

Electroencephalography
Electroencephalography has been used in many studies as a primary method for evaluating the meditating brain. Electroencephalography (EEG) uses electrical leads placed all over the scalp to measure the collective electrical activity of the cerebral cortex. Specifically, EEG measures the spikes in ion concentrations associated with action potentials in neurons. EEG has the benefit of excellent temporal resolution and is able to measure aggregate activity of portions or the entire cortex down to the millisecond scale. Unlike other imaging based methods, EEG does not have good spatial resolution and is more appropriately used to evaluate the running spontaneous activity of the cortex. This spontaneous activity is classified into four main classifications based on the frequency of the activity, ranging from low frequency delta waves (< 4Hz) commonly found during sleep to beta waves (13-30 Hz) associated with an awake and alert brain. In between these two extremes are theta waves (4-8Hz) and alpha waves (8-12 Hz).

Many studies on mindfulness meditation, assessed in a review by Cahn and Polich in 2006, have linked lower frequency alpha and theta waves to meditation. Much older studies report more specific findings, such as decreased alpha blocking and increased frontal lobe specific theta activity. Alpha blocking is a phenomena where the active brain, normally presenting beta wave activity, cannot as easily switch to alpha wave activity often involved in memory recall. These findings would suggest that in a meditative state a person is more relaxed but maintains a sharp awareness. Two large, recent comprehensive review works, however, point to poor control and statistical analyses in these early studies and comment that it can only be said with confidence that increased alpha and theta wave activity exists.

Neuroimaging
Functional magnetic resonance imaging (fMRI) is another highly utilized methodology for studying state changes in meditating brains. fMRI detects subtle increases in blood flow to areas of the brain with higher metabolic activity. Thus these areas of increased metabolic activity indicate which regions of the brain are currently being used to process whatever stimuli presented. Counter to EEG, the advantage of fMRI is its spatial resolution, with the ability to produce detailed spatial maps of brain activity. It suffers, however, in temporal resolution and cannot measure progressive activity, like the EEG, with much detail.

As a relatively new technology, fMRI has only recently been used to assess brain state changes during meditation. Recent studies have shown heightened activity in the anterior cingulate cortex, frontal, and prefrontal cortex, specifically in the dorsal medial prefrontal area during Vipassana meditation. Similarly, the cingulate cortex and frontal cortex areas were shown to have increased activity during Zen meditation. Both studies comment on the possibility that these findings could indicate some state of heightened voluntary control over attention during mindfulness meditation. Review works by Cahn and Chiesa state that these results indicate consistency in meditation’s effect on these regions of the brain, citing a multitude of other studies spanning other meditative disciplines, but mention the need for further investigation with better controls. The review by Cahn also notes findings describing a heightened emotional state of meditators. A more complex study, conducted in 2008 by Lutz et al, focused on emotional response during meditation. This investigation involved the creation of a “compassion meditation” state by novice and experienced meditators and testing the meditators response to emotionally charged sounds. fMRI results indicated heightened activity in the cingulate cortex but also in the amygdala, temporo-parietal junction, and right posterior superior temporal sulcus in response to the emotional sounds. The authors of this study believe this indicates greater sensitivity to emotional expression and positive emotion due to the neural circuitry activated.

Electroencephalography
Similar to research into state changes in brain function, older studies make more specific claims about trait changes in meditators versus non-meditators. Changes to the alpha wave were indicated to be a trait, as well as state, phenomena. Studies have reported an increase in the specific frequencies expressed in the alpha range, increased alpha band power, and an overall slowing (reduction in frequency) in EEG activity. The alpha blocking phenomena, observed as a state change in brain function, was investigated as a possible trait change as well. One study that examined a variety of meditation techniques tried to show that alpha blocking was effected by the long term practice of meditation by testing response to auditory stimuli. Review works, however, comment on inconsistent findings as well as a lack of repeated results in this, and other studies. They further remark that, similar to observations in brain state changes, only general assertions can be made about brain trait changes: some change in the electroencephalographic profile exists but with some inconsistency.

Neuroimaging
Brain trait changes have also been observed in neuroimaging studies, most often employing fMRI. A long-term increase in activity was discovered in the prefrontal cortex, the right anterior insula, and right hippocampus, suggesting an heightened ability to control attention and awareness. The review by Chiesa attribute these findings to the direct attention to and awareness of bodily sensations. One neuroimaging study also found some evidence for protection against the natural reduction in grey matter volume with aging, which could suggest a better attentiveness in aging meditators versus non-meditators.

Clincal Applications
A host of other studies have investigated the use of meditation as a psychotherapy to induce trait changes and treat various diseases and disorders. Since state and trait change investigations point to a heightened control of attention, one study attempted to improve this ability in patients characterized by a reduced aptitude for attention and focus. This study, by Harrison et al in 2004, implemented a 6-week yoga-based mindfulness meditation therapy for adolescents with attention-deficit hyperactivity disorder and reported significant reductions in the symptoms of these patients. Several other studies also reported findings that indicate an increased attentional ability in a clinical setting, specifically noting an ability to maintain attention despite unexpected stimuli.

Brain activity in the amygdala, cingulate, and frontal cortex areas seems to suggest that meditation has an impact on mood and emotion as previously discussed. Clinical studies have attempted to deploy this effect to treat emotional disorders and several studies have showed significant success in using mindfulness meditation to treat depression. These studies demonstrated that meditation was statistically effective at combating depression as well as preventing it. Another similar study cited success in reducing depression relapse, especially in patients that have relapsed three or more times.

Many other clinical applications such as anxiety disorders, stress, as well as physiological disorders have been investigated. Results tend to be inconsistent and not always repeatable. However, most studies that look at trait changes, whether applied clinically or not, on a general level reinforce the consistent state changes that have been observed. This would seem to suggest a neuroplastic mechanism that reinforces these state changes over time with continued meditation. Both Cahn and Chiesa are adamant about the need for further and more exhaustive research before more conclusions can be made.