Electroencephalography (EEG) | Can We See Our Brain's Activity in Real-Time?

Electroencephalography, or EEG, is a non-invasive neurophysiological monitoring technique used to record the electrical activity of the brain. This activity is generated by the billions of neurons in the brain, which communicate with each other through tiny electrical impulses. When a large number of neurons fire in synchrony, they produce an electrical field that is strong enough to be detected by electrodes placed on the scalp. These electrodes are small metal discs, typically attached to a cap or individually pasted onto the scalp using a conductive gel, which helps in transmitting the weak electrical signals. The signals captured by the electrodes are then amplified by specialized hardware because they are extremely small (in the microvolt range). The amplified signals are digitized and displayed on a computer screen as a series of wavy lines, which are known as brainwaves. Clinicians and researchers analyze these brainwaves based on their frequency (how fast they oscillate) and amplitude (how high the peaks of the waves are). Different frequencies are categorized into bands such as Delta (slowest waves, associated with deep sleep), Theta (associated with drowsiness or deep meditation), Alpha (present during relaxed wakefulness), Beta (seen during active thinking and concentration), and Gamma (highest frequency, related to complex cognitive processing). By examining these patterns, it is possible to assess brain function, detect abnormalities, and understand the neural dynamics underlying various cognitive states.

While EEG, functional Magnetic Resonance Imaging (fMRI), and Magnetoencephalography (MEG) are all methods for studying brain activity, they measure different things and have distinct advantages. EEG's primary strength is its excellent temporal resolution, meaning it can measure brain activity almost instantaneously, on a millisecond-by-millisecond basis. This makes it ideal for studying the precise timing of cognitive processes. However, its spatial resolution is limited; it is difficult to pinpoint the exact location deep within the brain where the signals originate. In contrast, fMRI measures changes in blood flow, a slower process that is an indirect marker of neural activity. Its temporal resolution is poor (on the order of seconds), but it offers superior spatial resolution, allowing for detailed 3D maps of brain activity. MEG is a third technique that detects the magnetic fields produced by the brain's electrical currents. It offers excellent temporal resolution, similar to EEG, and better spatial resolution than EEG, though not as good as fMRI. The choice of technique depends entirely on the research question: for understanding 'when' a cognitive process happens, EEG is superior; for knowing 'where' it happens, fMRI is the better tool.

EEG data provides a direct window into the real-time functional state of the brain. Different patterns of brainwave activity are reliably associated with distinct mental and physiological states. For example, a predominance of Alpha waves, particularly over the posterior regions of the brain, is a clear indicator of a relaxed, wakeful state with eyes closed. When a person becomes alert and opens their eyes or engages in a mentally taxing task, these Alpha waves are typically replaced by faster Beta waves. During the stages of sleep, the EEG shows a characteristic progression from Theta to Delta waves as sleep deepens. Clinically, EEG is invaluable for diagnosing and managing epilepsy, as seizures are caused by abnormal, hypersynchronous electrical discharges in the brain that are clearly visible on an EEG recording. It is also used to detect brain dysfunction caused by conditions like coma, encephalopathy, or brain death.

The EEG procedure is extremely safe, non-invasive, and painless. It does not involve any radiation, injections, or passing of electricity into the body. The electrodes are passive sensors; they only record the electrical signals that the brain naturally produces. The primary source of discomfort, if any, is the process of applying the electrodes. A technician will measure the head and mark the electrode positions, after which the electrodes are attached using a special conductive paste or gel. This can feel a bit strange and messy, and individuals with sensitive skin might experience minor irritation from the gel. For those using an electrode cap, the cap fits snugly on the head, which can feel tight for some. The recording process itself is simple: the individual is asked to sit or lie still, sometimes performing simple tasks like opening and closing their eyes or breathing deeply. The entire procedure, from setup to completion, typically lasts between 30 to 60 minutes.

Brain-Computer Interfaces (BCIs) are revolutionary systems that create a direct communication pathway between the brain and an external device. EEG is a cornerstone technology for non-invasive BCIs due to its portability, relatively low cost, and excellent temporal resolution. In an EEG-based BCI system, a person wears an EEG cap to record their brainwaves. They are then trained to generate specific brain activity patterns intentionally. For instance, a user might be asked to imagine moving their left or right hand. This motor imagery produces distinct and detectable changes in the brain's electrical activity over the motor cortex. Sophisticated machine learning algorithms are used to decode these patterns in real-time and translate them into commands. These commands can then be used to control a variety of devices, such as a computer cursor, a prosthetic limb, or a wheelchair. This technology holds immense promise for restoring communication and movement to individuals with severe neuromuscular disorders like amyotrophic lateral sclerosis (ALS) or spinal cord injuries, granting them greater independence and quality of life.