In the fall of 2005, the Dalai Lama gave the inaugural Dialogues between Neuroscience and Society lecture at the Annual Meeting of the Society for Neuroscience in Washington, DC. There were over 30,000 neuroscientists registered for the meeting, and it seemed as if most of them attended the talk. The Dalai Lama’s address was designed to highlight the areas of convergence between neuroscience and Buddhist thought about the mind, and to many in the audience he clearly achieved his objective. There was some controversy over his being invited to deliver this lecture insofar as he is both a head of state and a religious leader, and for that reason he largely stuck to his prepared text. But he strayed from the text at least once, reminding the audience that not only was he a Buddhist monk but also an enthusiastic proponent of modern technology.
Elaborating, he shared a confidence with the audience, telling the audience of scientists that meditating was hard work for him (even though he meditates for 4 hours every morning), and that if neuroscientists were able to find a way to put electrodes in his brain and provide him with the same outcome as he gets from meditating, he would be an enthusiastic volunteer. It turns out that a recent set of experiments, from researchers at MIT and Stanford, moves us a step closer to making his wish a reality.
The Dalai Lama’s interest in neuroscience has been reciprocated by at least some members of the neuroscience community. Reasoning that studying the brains of people who meditate might lead to novel insights about the human brain, investigations of long-term meditators has been fertile ground for scientific investigation, with some of the more rigorous work emerging from Richard Davidson’s laboratory at the University of Wisconsin. From the perspective of neuroscience, meditation can be characterized as a series of mental exercises by which one strengthens one’s control over the workings of their own brain. The simplest of these meditation practices is ‘focused attention’ where one concentrates on a single object, for example one’s breath. When expert meditators practiced focused attention meditation, demonstrable changes were seen using fMRI in the networks of the brain that are known to modulate attention. A second set of experiments studied long-term meditators practicing ‘open monitoring meditation’, a more advanced meditation practice which in many ways is a form of metacognition: the objective is not to focus one’s attention but rather to use one’s brain to monitor the universe of mental experience without directing attention to any one task. The unexpected result of this experiment was that the EEG of long-term meditators exhibited much more gamma-synchrony than that of naive meditators. Moreover, normally human brains produce only short bursts of gamma-synchrony. What was most remarkable about this study was that long-term meditators were able to produce sustained gamma-activity in a manner that had never previously been observed in any other human. As such, sustained gamma activity has emerged as a proxy for at least some aspects of the meditative state.
But what causes gamma rhythm? And are there any potential benefits of sustained gamma-activity? The strongest hypothesis for the cellular mechanisms underlying generation of the gamma rhythm is that it is due to the activation of fast-spiking interneurons in the cerebral cortex. In two new papers to be published in Nature, the laboratories of Christopher Moore and Li-Huei Tsai at MIT and Karl Deisseroth at Stanford tested this hypothesis directly. The experimenters utilized optogenetics, developing custom-designed viruses to infect only the fast-spiking interneurons of either the prefrontal or barrel cortex in mice with genetically engineered, light-sensitive cation channels. Then, they inserted fine optical fibers into the relevant region of the cortex, allowing light to be delivered to the infected neurons and thereby activating only the fast-spiking interneurons. (In essence, this allowed them to switch particular brain cells on and off.) In both experiments, selectively stimulating the fast-spiking interneurons evoked gamma oscillations, thereby confirming the hypothesis that these neurons drive the gamma rhythm.