Brain waves are oscillating electrical voltages in the brain measuring just a few millionths of a volt. There are five widely recognized brain waves, and the main frequencies of human EEG waves are Gamma(Ɣ), Beta(β), Alpha(𝛼), Theta(𝛳), Delta(δ). Delta waves have a frequency of 0.5-3 Hz and represent a brain state of deep sleep. Theta waves have a frequency of 3.5-7 Hz and represent a brain state of deep relaxation and focus. Alpha waves have a frequency of 7.5-12 Hz and represent a brain state of passive attention. Beta waves have a frequency of 13-30 Hz and represent a brain state of active attentiveness. Gamma waves have a frequency of 31-50 Hz or higher and represent a brain state of active concentration.
EEG waveforms vary based on the band, which denotes the frequency range. The delta band is the slowest wave with the highest amplitude, having a frequency range below 4 Hz. For adults, it is located in the front of the head, while for children it is located at the back of the brain. The theta band is between 4 to 7 Hz and is most common in young children while signifying drowsiness or arousal in adults. This band tends to spike due to an active inhibition of a movement or response. The alpha band is between 8 to 14 Hz, and it is correlated to eye muscle movements. It is located on both sides of the head’s posterior regions. The beta band is above 14 Hz and is correlated with general motor behavior. It is located on both sides of the head’s frontal regions. A further breakdown is here:
An electroencephalogram (EEG) is a method of testing electrical signals in the brain. It is often applied as a technique for data analysis such as time and frequency series analysis. The brain’s neurons contain ionic current, which creates voltage fluctuations that EEG can measure. This electrical activity is spontaneous and recorded over a period of time from many scalp electrodes to form an EEG signal.