- Electroencephalography (EEG) is a non-invasive neurophysiological technique used to record the electrical activity of the brain through electrodes placed on the scalp. These recordings reflect the summed postsynaptic potentials—primarily from cortical pyramidal neurons—that occur as a result of synchronous neuronal activity.
- Because neurons communicate using electrical signals, EEG provides a direct measure of brain function in real time, with millisecond-level temporal resolution, making it one of the most effective tools for studying the dynamic processes of the human brain. Unlike structural imaging techniques such as MRI or CT scans, EEG focuses on functional brain activity, allowing researchers and clinicians to observe patterns associated with cognition, consciousness, sleep, and neurological disorders.
- The EEG signal is captured by a set of electrodes arranged in a standardized configuration (such as the 10–20 system), which enables consistent placement across individuals and studies. These electrodes detect fluctuations in voltage differences between different scalp locations as neurons fire, producing characteristic waveforms across various frequency bands. The major EEG frequency bands include delta (0.5–4 Hz), theta (4–8 Hz), alpha (8–13 Hz), beta (13–30 Hz), and gamma (>30 Hz). Each frequency is associated with different brain states: for instance, alpha waves are typically observed during relaxed wakefulness with closed eyes, delta and theta waves dominate during sleep, and beta and gamma waves are associated with active thinking and sensory processing.
- Clinically, EEG is an essential diagnostic tool in neurology. It is most commonly used to diagnose and monitor epilepsy, where it can detect abnormal, hypersynchronous discharges known as epileptiform activity, such as spikes, sharp waves, and seizure patterns. EEG is also employed in the assessment of coma and brain death, sleep disorders (such as narcolepsy and parasomnias), encephalopathies, and monitoring anesthesia depth. In intensive care units (ICUs), continuous EEG (cEEG) is used to detect non-convulsive seizures and monitor cortical activity in critically ill patients. Furthermore, EEG-based methods like evoked potentials can be used to evaluate the functional integrity of specific sensory pathways.
- In research settings, EEG is widely utilized in cognitive neuroscience, psychology, and brain-computer interface (BCI) development. Its high temporal resolution makes it ideal for investigating rapid neural processes underlying attention, memory, language, and decision-making. Advanced EEG analysis techniques—including spectral analysis, event-related potentials (ERPs), source localization, and connectivity mapping—allow for deeper insights into functional brain networks. Despite its limited spatial resolution compared to imaging techniques like fMRI, EEG is more portable, less expensive, and safer (as it involves no radiation), which makes it suitable for both clinical and research applications in a variety of populations, including children and patients with mobility challenges.
