Your brain creates simple electricity through an electrochemical process measured in the form of brainwaves. Brainwaves occur at different frequencies depending on what the brain is doing.

By measuring these frequencies, using qEEG, it is possible to see where the brain is functioning less optimally.

Results from the Quantitative EEG are presented as Z scores, which are standard deviations from a sample of brain map recordings from databases of healthy individuals of a similar age. The Z Scores range from -3 to +3 based on the number of standard deviations from normal. The Z-scores are placed on brain maps and color-coded according to the positive or negative deviation. A score of 0 represents the norm and is color-coded green, red shows excessive activity (positive deviation) and blue shows diminished activity (negative deviation). [example image here]

How Brainwaves are Classified
Brainwave activity occurs on a continuum from slow to fast wave frequencies. For measurement, these brainwave frequencies are separated into five categories based on their repetitions per second (Hz) or cycles per second (cps). The brainwave frequency bands used for clinical purposes are:

Delta. These brain waves are the slowest brainwaves and are present primarily during sleep or when in a non-aroused state. They should not be excessive during an awake state. If seen in an awake state, theses waves may suggest issues related to depression, closed-head injury and learning disorders.
Theta. Theta waves are present when we are daydreaming or fantasizing and are commonly associated with creativity and intuition. Interestingly, the lower range of Theta waves are present during the time between waking and sleep when we are feeling very calm, serene and in drifty states.
Higher range of Theta brainwaves are commonly found when we are engaging in complex, inwardly-focused problem solving – like doing math problems in our head. People in a deep meditative or hypnotic state will also have high frequency Theta waves. A presence of excessive Theta waves during a normal awake state could reflect problems with focus and attention, head injuries, and learning disorders.

Children and adults with ADHD will produce excessively lower frequency Theta waves.

Alpha. These brainwaves are associated with a state of relaxation. Alpha waves will occur when our brains shift into a relaxed and disengaged or idle state. By closing our eyes and picturing something peaceful, we will quickly increase our Alpha brainwaves. Excessive frontal Alpha activity is often associated with adult ADD/ADHD and depression.
Beta. Beta waves are present when we are in a state of mental or intellectual activity and outward focus, like when we are thinking, problem-solving, processing information or feeling anxious. However, people with excessively high Beta activity may have conditions such as anxiety, obsessive-compulsive disorder, irritability, agitation, insomnia, bipolar tendencies, and substance abuse.
Gamma. Gamma waves are the fastest measured brainwaves and are considered essential for information and sensory-binding and are present during cognitive thought when the brain is processing and linking information from all parts of the brain. High amounts of Gamma brainwave activity is often associated with high levels of intelligence, enhanced memory, compassion and natural feelings of contentment.
A deficiency in Gamma brainwaves is often seen in individuals with learning difficulties, diminished mental processing and cognitive decline.

At any given time, everyone has a mix of these brainwaves present in different parts of the brain. The important factor for psychologists is to make sure the brainwave activity is appropriate for the emotional state or cognitive function.