How Does An EEG Work?
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EEG (electroencephalography) records electrical activity from the brain using small electrodes placed on the scalp. The brain's neurons generate tiny electrical signals as they communicate. EEG electrodes detect these signals through the skull, amplifying them millions of times to produce visible recordings. EEG is used to diagnose seizures, sleep disorders, and other neurological conditions.
EEG (electroencephalography) is one of medicine's most important tools for understanding brain function, recording the electrical activity of billions of neurons in real time. From diagnosing epilepsy to studying sleep to understanding consciousness, EEG provides unique insights into how the brain works. Understanding how EEG works reveals both the technology and the underlying biology of brain electrical activity.
What is an EEG?
EEG (electroencephalography) is a technique for recording the electrical activity of the brain through electrodes placed on the scalp. It was first developed by German physician Hans Berger in 1924. The brain contains about 86 billion neurons that communicate through electrical signals, generating detectable patterns of voltage at the scalp surface. Modern clinical EEG typically uses 19-32 electrodes; research EEG can use 64-256 electrodes. The recordings show ongoing brain activity as wavy lines for each electrode location, with patterns reflecting underlying neural activity. EEG is non-invasive, safe, and relatively inexpensive.
How are EEG signals recorded?
EEG works by detecting voltage changes at the scalp produced by neural electrical activity. Many neurons firing in synchrony create electrical fields that can be measured at the scalp despite the skull and skin reducing the signals significantly. The raw signals are extremely small (microvolts), so electrodes connect to amplifiers that magnify them millions of times. The amplified signals are displayed on screens or recorded digitally. The standard 10-20 system places electrodes at specific scalp locations relative to skull landmarks. Gels or pastes between electrodes and scalp ensure good electrical contact. A typical EEG session lasts 20-60 minutes.
What can EEG show?
EEG reveals patterns of brain electrical activity that doctors interpret for clinical purposes. Common uses include diagnosing epilepsy (seizures show characteristic patterns), evaluating sleep disorders, monitoring brain function during surgery or coma, identifying brain damage or tumors (sometimes), and confirming brain death. EEG can also show normal brain rhythms during different states: alpha waves (8-13 Hz) when relaxed with eyes closed, beta waves (13-30 Hz) when alert, theta waves (4-7 Hz) during drowsiness, delta waves (0.5-4 Hz) during deep sleep. Research uses include studying cognition, attention, and consciousness.
What are EEG patterns?
EEG signals contain various wave patterns at different frequencies, each associated with different mental states. Delta waves (0.5-4 Hz, largest amplitude) dominate during deep sleep. Theta waves (4-7 Hz) appear during drowsiness and meditation. Alpha waves (8-13 Hz) appear during relaxed wakefulness with closed eyes. Beta waves (13-30 Hz) appear during active thinking and concentration. Gamma waves (30-100 Hz) may relate to cognitive processing. Abnormal patterns include spike-wave discharges (in epilepsy), focal slowing (over brain damage), and various other patterns. Combined with patient symptoms, EEG patterns guide diagnosis and treatment.
EEG (electroencephalography) records electrical activity from the brain using small electrodes placed on the scalp. The brain's neurons generate tiny electrical signals that are amplified millions of times to produce visible recordings. Different brain wave patterns (delta, theta, alpha, beta, gamma) reflect different mental states. EEG is used to diagnose epilepsy, sleep disorders, brain damage, and other conditions, plus extensive research applications.
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