Our nervous system is a network of billions of neurons that communicate with one another via electrical messages. The human cerebral cortex, the outermost layer of the brain is only 1/8th inch (3 mm) thick and contains 10 billion neurons, each with tens of thousands of interconnections, or synapses. Each individual neuron generates voltage spikes that are passed on to other neurons at the synapses. Spikes from a single neuron in the cortex are too weak to be detected on the surface of the scalp, but when millions of neurons, aligned in parallel and having the proper orientation fire synchronously, then the combined signal can be detected on the surface of the skin (There are roughly 10 million neurons in 1 cm2 of the cortex). The combined signal, generated by the synchronized firing of large populations of neurons can be measured in the range of a few hundred microvolts between sensor and reference electrodes.
The electroencephalograph (EEG) is a device for measuring electrical oscillations on the scalp. The first electroencephalogram of human brain waves was recorded by Hans Berger in 1924. Over the years, EEG recording devices have become increasingly sensitive and sophisticated. Today, there are several devices available costing less than $1000 that have multiple electrodes and are capable of wireless connectivity with personal computers. This investigation used a Muse Headband from InteraXon.
For a brief tutorial on brainwaves, see the Understanding Brainwaves post.
In my first experiments with the Muse I looked for differences between eyes closed and eyes open during meditation.
In a next series of experiments, I compared brainwaves during meditation (e.g., counting or following the breath) with brainwaves during non-meditative states such as drinking a cup of tea, reading, thinking of things (e.g., tools, people) and worrying.
In an effort to look for changes in EEG patterns over the course of a meditation retreat, I made daily recordings during a 7-day sesshin (meditation retreat).
In a pilot study of highly trained meditators, I recorded brainwaves of four Zen practitioners with experience of ~10,000 hours or greater.
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