Brain activity and meditation
Meditation and its effect on the central nervous system has become a focus of collaborative research in neuroscience, psychology and neurobiology during the latter 20th century. Research on meditation sought to define and characterize various practices. Meditation’s effect on the brain can be broken up into two categories: state changes and trait changes, respectively alterations in brain activities during the act of meditating and changes that are the outcome of long-term practice.
Mindfulness meditation is frequently studied, a Buddhist meditation approach found in Zen and Theravada/Vipassana. Jon Kabat-Zinn describes mindfulness meditation as a complete, unbiased attention to the current moment.
Changes in brain state
Electroencephalography (EEG) has been used in many studies as a primary method for evaluating the meditating brain. Electroencephalography uses electrical leads placed all over the scalp to measure the collective electrical activity of the cerebral cortex. Specifically, EEG measures the electric fields of large groups of 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 (< 4 Hz) 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 (4–8 Hz) 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 phenomenon 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.
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.
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 cortex, 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.
Study on meditation and emotion
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.
Changes in brain due to prolonged practice of meditation
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 in experienced meditators versus less experienced meditators while meditating. 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 affected by the long term practice of meditation by testing response to auditory stimuli.
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 a 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.
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.
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