Gamma waves are commonly associated with consciousness in the brain. In fact, Gamma is often called the frequency band of “higher consciousness”, because it is present when people are awake and paying attention, it is reduced during sleep, and disappears altogether during loss of consciousness such as when under anesthesia.
A variety of cognitive activities have been associated with gamma (40 hz in particular) – attention, memory, facial recognition, REM sleep and the comprehension of new concepts, to name a few. Most importantly, gamma is thought to be important to binding, or the ability of the brain to combine all input, external and internal, into a single unified conscious experience.
High amplitude gamma is often exhibited by experienced meditators. An interesting study by Antoine Lutz, of the National Academy of Sciences USA, analyzed 2 groups of people while meditating. The first group consisted of students trained for a single week in meditation, while the second group had at least 15 years of meditation training and experience. Under an EEG, the experienced meditators exhibited far greater amounts of gamma amplitude and phase synchrony, leading many to believe that long-term meditation actually increases conscious awareness. (For those who are interested, this was during what is called “compassion meditation”, or a state of compassion not directed at any particular source. I wonder if the same result would be derived with other traditional types of meditation?)
Gamma frequencies and phase synchrony have even been tested in robotics and neural networks, lending some intriguing evidence to the gamma-consciousness theory – but that is a story for a different post.
In contrast, Alpha frequencies are usually associated with an idle, quiet mind. Alpha frequencies are increased when you close your eyes, day dream, or when your attention starts to wander. Therefore, Alpha has not really been considered a candidate for active participation in attention and consciousness.
But new evidence presents a different theory. A recent study by Palva and Palva, of the University of Helsinki, suggests that Alpha plays a crucial role in consciousness by interacting with other frequency bands. Alpha rhythms seem to “lock” on to other frequencies by synchronizing with their phase, and this appears to happen particularly with stimuli that are consciously perceived – something normally associated with Gamma!
The study also found that the presence of alpha prior to visual stimuli correlated with better cognitive performance. Chris Chatham, of Developing Intelligence, concludes that this is because alpha “calms the waters” in the cortex prior to receiving a visual stimulus, so that it can be more easily detected.
In prior studies, a higher Peak Alpha Frequency has been associated with greater intelligence and a more mature brain. In other words, it is good sign to have a peak alpha frequency in the 10-12 hz range rather than 7-9 hz.
It is interesting to note that a faster brain (more Beta) doesn’t always mean you will be smarter, in the same way a deep, quiet brain dominated by low frequencies isn’t always what you find when you analyze meditation. The more we look at how frequencies interact with each other, the more it seems that all frequencies play some role in a wide variety of tasks.