Our brain is made up of billions of brain cells called neurons, which utilize electricity to communicate with each other. The synergy of millions of neurons sending signals at once creates a huge amount of electrical activity in the brain, which can be observed using sensitive medical equipment (such as an EEG), assessing electricity levels over areas of the scalp. The mix of the electrical activity of the brain is commonly called a Brainwave pattern, because of its cyclic, 'wave-like' phenomena. Our mind regulates its activities by means of electric waves which are registered in the brain, emitting tiny electrochemical impulses of varied frequencies, which can be recorded by an electroencephalogram. These brainwaves are known as:
- Beta emitted when we are consciously alert, or we feel agitated, tense, afraid, with frequencies ranging from 13 to 60 pulses per second in the Hertz scale.
- Alpha when we are in a state of physical and mental relaxation, although aware of what is happening around us, its frequency are around 7 to 13 pulses per second.
- Theta more or less 4 to 7 pulses, it is a state of somnolence with reduced consciousness.
- Delta when there is unconsciousness, deep sleep or catalepsy, emitting between 0.1 and 4 cycles per second.
Source: http://www.doctorhugo.org/brainwaves/brainwaves.html