Now, scientists are using cutting-edge scanning technology to watch the meditating mind at work. They are finding that regular meditation has a measurable effect on a variety of brain structures related to attention - an example of what is known as neuroplasticity, where the brain physically changes in response to an intentional exercise.
A team of Emory University scientists reported in early September that experienced Zen meditators were much better than control subjects at dropping extraneous thoughts and returning to the breath. The study, "'Thinking about Not-Thinking:' Neural Correlates of Conceptual Processing During Zen Meditation," published by the online research journal PLoS ONE, found that "meditative training may foster the ability to control the automatic cascade of semantic associations triggered by a stimulus and, by extension, to voluntarily regulate the flow of spontaneous mentation."
The same researchers reported last year that longtime meditators don't lose gray matter in their brains with age the way most people do, suggesting that meditation may have a neuro-protective effect. A rash of other studies in recent years meanwhile have found, for example, that practitioners of insight meditation have noticeably thicker tissue in the prefrontal cortex (the region responsible for attention and control) and that experienced Tibetan monks practicing compassion meditation generate unusually strong and coherent gamma waves in their brains.
"There are a lot of potential applications for this," said Milos Cekic, a member of the Emory research team and himself a longtime meditator. He suspects the simple practice of focusing attention on the breath could help patients suffering from depression, anxiety, post-traumatic stress and other conditions characterized by excessive rumination.
Meanwhile, a meditation-derived program developed at the University of Massachusetts called Mindfulness Based Stress Reduction (MBSR) is gaining popularity for treatment of anxiety and chronic illnesses at medical centers around the U.S.
As far back as the 1960s, Japanese scientists who used electroencephalograms (EEG) to measure the brain waves of Zen monks found characteristic patterns of activity. But the advent of functional magnetic resonance imaging (fMRI) in the 1990s gave researchers a chance to see brains functioning in real time. Functional MRIs measure the blood flow in different parts of the brain, which correlates with how active they are.
The Emory team, which also included Giuseppe Pagnoni and Ying Guo, wanted to see whether Zen meditators were indeed better than novices at controlling the flow of thought, as meditators themselves report. Cekic and Pagnoni asked a dozen seasoned Zen meditators - including several monks - and a dozen control subjects to perform a simple cognitive task while undergoing an fMRI scan. The Zen practitioners all had at least three years of daily practice experience, while the control group members had none.
Inside the scanner, the subjects were all asked to follow their breathing while looking at a screen on which words or wordlike combinations of letters were flashed at irregular intervals. Students had to decide whether they were seeing a real word or a made-up word and signal by pressing a button and then return to focusing on their breathing.
The random word or letter combinations engaged what is sometimes called the "default semantic network," a resting state in which words and thoughts arise spontaneously - what we experience as mind wandering, Cekic said. Practitioners of zazen (seated Zen meditation) are taught to notice when the mind has started to wander and quickly return attention to the breath.
When the word or letter combinations flashed on the screen, the experienced meditators were quickly able to leave the default state and return to their breathing, Cekic says. "You have these extended reverberations in the semantic network after you give people a word," Cekic said. "The meditators pretty much turn it off as soon as it's physiologically possible, while the non-meditators don't."
This is the second set of findings to have come from the fMRI experiments, Cekic said. Although people lose neurons - gray matter - and have more trouble concentrating as they age, the study published last year by the Emory team found this wasn't true of the Zen practitioners.
"What we saw in the meditators was pretty much a straight line," Cekic said. "There was no decrease with age in their gray-matter volume." There was also no decline in attention - in fact, the effect of meditation on gray matter was most pronounced in the putamen, a brain structure linked to attention. "We can't say causally that meditation prevents cell death, but we did see in our sample that the meditators did not see a gray matter loss with age," Cekic said.
Meanwhile, Harvard University researcher Sara Lazar made headlines in 2005 when she reported that Western practitioners of insight meditation - a non-judgmental awareness of present-moment experience that resembles zazen - had significantly thicker tissue in their prefrontal cortex and insula than non-meditators.
Lazar, who practices insight meditation and yoga, performed fMRI scans on 20 experienced meditators and 15 controls with no meditation experience. Lazar said that because earlier research had mostly been conducted on monks, she wanted to see whether the once-a-day meditation sessions typical of most American meditators might affect brain structures.
Unlike earlier research, which had focused on brain waves or measured neural blood flow, Lazar's experiment yielded the first concrete evidence linking meditation practice to changed brain structure. "The nice thing about (studying) the structure is it's something solid," she said. "It's not performance on a task. It's your brain."
Lazar says it's too soon to tell whether meditation causes new gray matter to form or whether it protects against the normal decline of brain volume. The greatest contrasts were seen between the cortical tissue of meditators and control subjects who were in their 40s and 50s, she says, while the insula, which integrates sensory processing, was thicker in meditators of all ages.
Future research will require longitudinal studies - following subjects through time - to see whether or not meditation is causing the neural changes. "Maybe meditators are weird," Lazar said, suggesting that perhaps people with unusual brains are especially drawn to meditation.
Where does all this lead?
Andrew Newberg, a University of Pennsylvania researcher who has written such popular books as Why We Believe What We Believe and who has conducted brain scans of meditating Tibetan monks and Franciscan nuns engaged in contemplative prayer, believes the science shows meditation works.
"The overwhelming evidence is that meditation has benefits," he said. "If it makes your mind clearer and helps you focus your attention better, it should help people."
For more than a decade, Newberg has plumbed spiritual mysteries, using fMRI and SPECT (single photon emission computed tomography) to measure blood flow in the brains of not only meditators but people in the throes of other religious experiences, including speaking in tongues, as well.
"The fascinating thing to me is that when people have these mystical experiences, they not only describe it as real, but they describe it as more real than our everyday experience," he said. It raises the question of just what is real.
"I recognize that studying some of the things I study may get me to an answer," he added. "A lot of this has been my own spiritual journey, which has become a lot more meditative and contemplative."
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