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Brain waves are patterns of electrical activity resulting from millions of neurons firing in the brain. An electroencephalogram, or EEG, measures these waves by placing electrodes on the scalp to detect electrical signals and transmit them to a computer for analysis. EEG is used to study brain function, monitor disorders, and assess neurological health.

Alpha waves are low-amplitude rhythmic waves with a frequency of 8-13 Hz that appear in healthy adults during wakeful rest with eyes closed. They diminish when a person concentrates on specific tasks or enters sleep. Alpha waves reflect a relaxed, alert mental state without active mental engagement.

Beta waves have a frequency of 14-30 hertz and occur when a person is mentally alert and focused on specific tasks. They are typical during problem-solving, planning, or active concentration. Beta waves indicate heightened cognitive engagement and conscious mental activity.

Theta waves have a frequency of 4-7 hertz and are typically present in children. In adults, they appear during emotional stress or transiently during sleep. In wakeful adults not under stress, theta waves may indicate tumors or other pathological brain conditions requiring medical evaluation.

Delta waves are high-amplitude, low-frequency waves present at 1-5 Hz during the deepest levels of sleep in adults and in awake infants. In wakeful adults, delta waves may signal brain damage or neurological injury. Their presence during sleep is normal and reflects restorative brain activity.

An EEG can detect various neurological disorders including epilepsy, dementia, stroke, and traumatic brain injury. It monitors changes in mental state over time and can indicate brain death when waves are absent. EEG is also valuable for assessing learning and memory functions through brain activity patterns.

Brain wave patterns shift across consciousness states: alpha waves dominate relaxed wakefulness, beta waves appear during active mental tasks, theta waves emerge during emotional stress or sleep transitions, and delta waves characterize deep sleep. These transitions reflect the brain's electrical activity adjusting to different cognitive and physiological demands throughout the sleep-wake cycle.