Electroencephalography (EEG) | Can We See Our Brainwaves in Real-Time?

Electroencephalography, or EEG, is a non-invasive neurophysiological monitoring technique used to record the electrical activity of the brain. The human brain consists of billions of neurons that communicate with each other through tiny electrical impulses. EEG measures these voltage fluctuations. The procedure involves placing small metal discs, known as electrodes, onto the scalp. These electrodes are connected by wires to a computer that amplifies the brain's electrical signals and records them as a series of wavy lines. Each line represents the electrical activity in a specific region of the brain. The key advantage of EEG is its excellent temporal resolution, meaning it can detect changes in brain activity that occur in milliseconds. This makes it an invaluable tool for observing the brain's rapid responses to stimuli or tracking physiological changes during different states of consciousness, such as wakefulness and sleep. The entire process is safe and painless; it does not involve sending any electricity into the brain but simply records the electrical signals that the brain naturally produces.

Brainwaves are categorized into five primary types based on their frequency, measured in Hertz (Hz). Each type is associated with different mental states. Delta waves (0.5-4 Hz) are the slowest and are dominant during deep, dreamless sleep. Theta waves (4-8 Hz) are associated with deep relaxation, meditation, and the early stages of sleep. Alpha waves (8-12 Hz) are present during quiet, resting states when the eyes are closed but the individual is awake and relaxed. Beta waves (12-38 Hz) are associated with normal waking consciousness, active thinking, focus, and problem-solving. Finally, Gamma waves (38-100 Hz) are the fastest brainwaves and are linked to high-level information processing, learning, and memory. The specific pattern and combination of these brainwaves provide critical insights into a person's cognitive and physiological state.

In clinical settings, EEG is a fundamental diagnostic tool for neurological disorders. Its most common application is in the diagnosis and management of epilepsy. By detecting abnormal electrical patterns, such as spikes and sharp waves, EEG can help pinpoint the area of the brain where seizures originate. It is also essential for diagnosing various sleep disorders, like insomnia and narcolepsy, by monitoring brainwave patterns throughout the sleep cycle. Additionally, EEG is used to assess brain damage after a head injury, stroke, or in patients with brain tumors, and to monitor brain function in comatose patients to determine the level of brain activity.

The EEG procedure is completely safe, non-invasive, and painless. It does not involve any radiation, and unlike some other imaging techniques, it requires no injections. The electrodes only record electrical activity from the brain; they do not transmit any electrical current to the scalp. Most people report feeling little to no discomfort during the test. The technician will use a sticky paste or a special cap to attach the electrodes to the scalp, which might feel slightly unusual but is not painful. During the recording, the patient is typically asked to relax, lie still, and at times, perform simple tasks like opening and closing their eyes or breathing deeply.

EEG and functional Magnetic Resonance Imaging (fMRI) are both powerful tools for studying brain activity, but they measure different things and have distinct strengths. EEG directly measures the brain's electrical activity, providing a high temporal resolution. This means it can track brain events on a millisecond scale, making it ideal for studying the precise timing of neural processes. In contrast, fMRI does not measure neural activity directly. Instead, it measures changes in blood flow and oxygenation (known as the BOLD signal), which is an indirect indicator of brain activity. fMRI offers superior spatial resolution, meaning it can pinpoint the location of brain activity with much greater accuracy than EEG. Therefore, EEG tells you 'when' an activity happens, while fMRI tells you 'where' it happens.