There is one middle frequency called Alpha that appears in all areas of the brain. Another, which only occurs in a specific area, is called Sensory-Motor Rhythm (SMR). Like slow frequencies, middle frequencies are broadcast by rhythm generators in the middle of the brain. Unlike the slow frequencies, which appear globally, middle frequencies are Regional. They dominate in specific areas.
Alpha (8-12 Hz) can be split into two bands—slow alpha (8-10 Hz) and fast alpha (10-12 Hz), each produced by a different generator. SMR can be defined as the frequency band above alpha.
Unlike fast and slow processing frequencies, middle frequencies represent pure awareness states. They form the bridge between subconscious and conscious minds, allowing us to be consciously aware of our own feelings and memories. Without this bridge, we tend to be stuck in conscious thought but unaware of the driving force of what we feel and recall or stuck in our dreamy wordless subconscious but poorly able to process consciously.
Slow frequencies can be described as Creative/Intuitive; fast as Logical/Rational. Middle frequencies are described as Still/Present. Clearly it would be ideal for our brains to be able to shift up and down the range of frequencies and sustain each when it is appropriate to the task at hand. Each has its strengths and weaknesses, so dominance of any carries with it limitations. But if we want to be able to shift into fast or shift into slow, then the obvious place to hang out is in the middle.
Stillness: The alpha state is quiet. It is blocked when cortical neurons are working (beta speeds), so it does not operate with words or thoughts.
Presence: Alpha is not internal, like the slow-frequency states. In alpha we are present in this time and this place, without future, without past.
The Observer: We have spoken previously about our Center, which is not a mental state. From our Center, we are aware of what is happening around us and within us. Stillness doesn’t necessarily mean that my mind has no thoughts. It means that I’m aware of a thought entering my mind, but I don’t hop onto it or try to push it away. The sun comes out from behind a cloud, a bell begins to chime, a thought comes into my mind. The observer state is aware of these but remains disconnected from them all.
Resting/ready: Alpha is a low energy state. The neurons are resting, wasting no energy, but able to activate into beta the moment a task appears. It is often called “The Zone”, or the Flow state. It can be a peak state.
Auto Pilot: In the alpha state, we can do things over which we have developed mastery. Many of us experience driving routine trips without having to watch every street sign, attend to every turn. We are aware of what is around us, and we have a routine for the trip that happens automatically if we let it. But when something unexpected happens, the alpha brain will burst into localized beta to respond.
Alpha for the body: SMR (sensory-motor rhythm) is an analogue of alpha stillness related to our bodies instead of our minds. SMR relates to a state of deep relaxation and stillness.
Sleep Issues: Inability to produce bursts of SMR in sleep (called sleep spindles) can result in sleep-onset insomnia, restless sleep, teeth-grinding and other such issues.
Alpha Peak Frequency: (10 Hz) is one of the most important measures of brain activity. As the strongest alpha frequency slows from 10 Hz, cognitive function and sleep often suffer.
Slow Alpha (8-10 Hz) is a frequency closely related to fast theta (6-8 Hz). It is a kind of hypnotic state, sometimes experienced as foggy, often with difficult recalling words.
Fast Alpha (10-12 Hz) is more the peak state discussed above. It is clear and aware.
When and where
Alpha frequencies are stronger in the rear of the brain, and especially over the right hemisphere. Left and frontal areas of high alpha dominance are often correlated with depression, negativity, low energy or motivation.
Alpha levels are expected to rise 30-50% during eyes-closed relaxation periods, where they often dominate the EEG. They generally drop into balance with other frequencies with eyes open.
When we see bursts of 12-15 Hz in the area called the Sensory-Motor cortex, which runs from side-to-side across the center of the top of the head, it is called SMR. Elsewhere, 12-15 Hz is called “Low Beta”, and it is considered a fast frequency.