Brain Waves

Electrical instruments (electroencephalographs) are commonly used by medical people to evaluate mental states. These instruments measure the neuron firing rates of groups of brain cells.  These firing rates are commonly thought to control mental states.  Beta, alpha, theta and delta are terms that medicine uses to indicate the rates of brain cell firing and the corresponding mental states associated with them.

 The Delta mind state is commonly experienced at night during deep sleep or possibly during the day by people experiencing depression or mental fatigue.  The Delta state of mind involves frequencies from approximately 0.1Hz to 4Hz.  The natural amplitudes are large in size.  These frequencies are the least researched and are common in very deep trance states. My personal favourites are from Dr Jeffrey Thompson. I have the theta and gamma Meditation System and I enjoy it every time I use it! The beta state is that state of mind that you experience when awake and active during the day.  It includes any brain wave with a frequency greater than or equal to 13 Hz (faster repetition than 13 times per second).  Beta states above 20 Hz are generally classed as higher beta or gamma.

The higher beta state, often referred to as the gamma state, is experienced while wide-awake and highly aroused.  The higher beta state is very stimulating and can be associated with anxiety.  This anxiety could be related to subconscious resistance to these states.  The brain wave amplitudes tend to be very small.  This is the type of frequency used in the Energizer programme.

The lower beta state is that state of mind commonly experienced while awake and busy during the day.  This is the state of mind in which you commonly deal with your daily routines.  You can experience anxiety with some of the lower beta frequencies.  The low beta state involves frequencies from 13Hz to 20Hz.  The amplitudes are generally quite small.  This type of frequency has been used successfully as a harmonic of lower frequencies to create unusual effects.

The Alpha State

The alpha mind state is that state commonly experienced while the body is resting and the mind is calm.  The alpha state is the one you experience whilst doing a mundane repetitive task with nothing particular on your mind.  A typical example would be driving a car (how many times have you driven from work and barely remembered the journey?).  The alpha state of mind involves frequencies from 8.0 to 12.9Hz.   The natural amplitudes tend to be larger than beta.  The alpha state is also characteristic of mild meditation and programs such as de Silva mind control, Stress Manager, autogenics, remote viewing and super relaxation. 
Note:  You can quickly induce alpha state by closing your eyes and generally looking upwards, allowing your eyes to roll backwards.

The Theta State

The theta state is commonly experienced in deepened states of meditation, at the onset and in lighter parts of sleep.  It seems to present in hypnogogic and hypnopompic hallucination.  It is characterized by frequencies from 4.0Hz to 7.9Hz.  It is believed by some scientists that high amplitude Theta frequencies accompany most (if not all) psychic activity.  
For more information on brain frequencies: http://www.simonheather.co.uk/pages/articles/brain_waves.pdf
and  http://www.sowter.co.uk/pdf/ultrasonichearing.pdf