An Electroencephalogram (EEG) is a non-invasive medical test that measures the electrical activity of the brain. Brain cells, called neurons, communicate with each other through tiny electrical impulses, and the EEG captures these signals. The test helps detect potential problems with brain cell communication and diagnose various brain conditions by showing changes in brain activity. These “squiggly lines” on an EEG recording represent the continuous electrical signals generated by the brain, even during sleep. Understanding these patterns can provide insights into brain function and aid in identifying neurological disorders.
The Basics of EEG Recording
An EEG records the brain’s electrical activity using small, metal discs called electrodes. These electrodes are carefully placed on the scalp, often after the skin is prepared with a gritty cream to enhance signal quality. In some cases, an elastic cap fitted with electrodes might be used. The electrodes are connected by wires to an instrument that amplifies the detected brain waves. This amplification is significant, often increasing the signal by as much as 10,000 times, as the brain’s electrical activity is measured in microvolts. The amplified signals are then displayed as wavy lines, or waveforms, on a computer screen or printed onto paper. This visual output allows medical professionals to observe the patterns of electrical impulses generated by the brain’s neurons.
Decoding Brainwave Patterns
Brain waves are patterns of electrical activity categorized by their frequency, measured in Hertz (Hz), and are associated with different mental states.
- Delta waves (0.5 to 4 Hz) are the slowest, typically ranging from 0.5 to 4 Hz. These waves are most prominent during deep, restorative sleep and are linked to physical and mental restoration.
- Theta waves (4 to 8 Hz) have a frequency range of 4 to 8 Hz and are often observed during light sleep or states of deep meditation. They are associated with creativity, intuition, and access to long-term memory.
- Alpha waves (8 to 13 Hz) appear when a person is relaxed but still alert, such as during light meditation or quiet rest. These waves are connected to mind-body coordination, mental relaxation, and can improve memory.
- Beta waves (13 to 30 Hz) are higher frequency waves, typically between 13 and 30 Hz. They are dominant during states of wakefulness and alertness, particularly when engaged in active thinking, problem-solving, or focused attention.
- Gamma waves (30 to 100 Hz or more) are the highest frequency, ranging from 30 to 100 Hz or more, and are involved in high-level cognitive functions, including learning and memory.
Identifying Deviations
An EEG can reveal deviations from normal brainwave patterns, suggesting underlying neurological issues. Abnormal EEG activity can manifest as distinct patterns that differ from the expected waveforms. These include spikes, which are sharp, brief electrical discharges lasting less than 70 milliseconds, and sharp waves, which are similar but last between 70 and 200 milliseconds. Both spikes and sharp waves are often associated with epilepsy and may indicate potential seizure activity.
Another type of deviation is generalized slowing, where the brain’s electrical activity consistently operates at lower frequencies, such as in the theta or delta range, during awake states. This can reflect diffuse cerebral dysfunction caused by conditions like encephalopathy, brain injury, or the effects of certain medications. Focal slowing, on the other hand, indicates a localized area of slowed activity, often suggesting a structural abnormality like a tumor or stroke in that specific brain region. The presence of rhythmic slowing can also suggest an epileptiform process.
Interpreting Findings
Reading an EEG involves integrating these findings with a patient’s overall clinical picture. A qualified medical professional, typically a neurologist or epileptologist, is essential for accurate interpretation. They consider the patient’s medical history, current symptoms, and results from other diagnostic tests. This holistic approach ensures that EEG findings are understood within the broader context of an individual’s health.
Factors such as certain medications, sleep deprivation, or even muscle movements and eye blinks can influence EEG readings and create artifacts that might mimic brain activity. Identifying these artifacts is a skill that comes with specialized training and experience. The duration and conditions of the recording, including whether the patient was awake, drowsy, or asleep, also play a role in interpretation. Professional medical expertise is crucial for a precise diagnosis and treatment plan.