An electroencephalogram (EEG) is a medical test that measures the electrical activity of the brain. It provides a visual representation of the brain’s ongoing electrical signals. This non-invasive procedure helps healthcare professionals observe how brain cells communicate through electrical impulses. The resulting wavy lines on a recording offer insights into brain function.
Understanding Brain Activity
The brain functions through a complex network of billions of specialized cells called neurons. These neurons communicate with each other by generating tiny electrical impulses.
When many neurons fire together in a synchronized manner, their collective electrical activity becomes strong enough to be detected from outside the skull. This summed electrical potential forms the basis of what an EEG records. The signals, though weak at the individual neuron level, are amplified to provide a measurable representation of brain function.
How EEG Signals are Recorded
An EEG recording involves placing small, flat metal discs called electrodes onto the patient’s scalp. These electrodes are strategically positioned according to a standardized system. A technician prepares the scalp and attaches the electrodes.
The electrodes are connected by wires to an EEG machine, which amplifies the faint electrical signals from the brain. This amplification is necessary because the skull and other tissues significantly attenuate the signals. The amplified signals are then recorded, appearing as a series of wavy lines that represent the brain’s electrical activity over time. The process typically causes little to no discomfort.
Deciphering EEG Waveforms
The EEG produces waveforms, each with distinct frequencies and amplitudes. These patterns, known as brainwaves, correspond to different states of consciousness and mental activity.
Delta waves (0.5 to 4 Hz) are slow and high-amplitude, predominating during deep sleep and in infants.
Theta waves (4 to 8 Hz) are associated with light sleep, drowsiness, and states of creativity or daydreaming.
Alpha waves (8 to 12 Hz) are prominent when a person is awake but relaxed.
Beta waves (14 to 30 Hz) are faster and smaller, indicating active, alert, and focused mental states.
Neurologists analyze these waveforms for deviations from normal patterns, which can indicate neurological conditions. Abnormalities might include unusually slow waves, excessively fast activity, or sharp spikes and waves. Interpreting these patterns requires specialized expertise to link specific electrical signatures to brain states and potential underlying issues.
When EEG is Used
EEG is widely used in clinical settings to diagnose and monitor various neurological conditions. Its primary application is in the diagnosis and management of epilepsy, where it helps identify abnormal electrical discharges associated with seizures. EEG can also assist in localizing the origin of seizure activity within the brain.
Beyond epilepsy, EEG plays a role in assessing sleep disorders to identify patterns indicative of conditions like sleep apnea or narcolepsy. It is also employed to evaluate brain function following head injuries, in cases of coma, or to confirm brain death. Researchers utilize EEG to study brain activity during various cognitive processes and states.