Brain waves are electrical signals generated by the neurons in the brain, which are regularly monitored to measure mental activities. Brain waves and their frequency ranges can be measured using an electroencephalogram or EEG. There are four main types of brain waves, each with distinct characteristics:

• Alpha Waves – Alpha brain waves, between 8 and 13 Hz ( Hertz), occur when a person is relaxed with eyes closed. The alpha waves then disappear when one is concentrating on specific tasks.
  
• Beta Waves – Beta brain waves, between 14 and 30 Hz, occur when an individual is awake and alert. This type of brainwave is typical when engaged in problem-solving or planning.
• Theta Waves – Theta brain waves, from 4 to 7 Hz, occur primarily in children. EEG of adults occasionally shows theta waves during periods of emotional stress. Their presence in adults not under any stress indicates the presence of tumors or other pathological conditions affecting the brain.
• Delta Waves – Delta brain waves have a shallow frequency at 1 to 5 Hz and are seen during an adult's deepest level of sleep. They are also seen in infants. Delta waves in wakeful adults may also indicate brain damage.

An EEG can detect various types of disorders, including epilepsy, dementia, stroke, and traumatic brain injury (TBI). It can also be used to monitor for changes in an individual's mental state over time. The test is usually performed by placing electrodes on the scalp, which detect electrical signals from the brain and transmit them to a computer for analysis.