An Electroencephalogram (EEG) is a non-invasive method used to record the brain’s spontaneous electrical activity. This technique helps in understanding brain function by detecting tiny electrical signals generated by brain cells. EEG channels are the specific sensors or electrodes placed on the scalp that capture these electrical impulses. They play a role in providing a comprehensive view of brain function by collecting data from multiple points simultaneously.
What Are EEG Channels?
EEG channels are electrodes placed on the surface of the scalp. These electrodes detect the minute electrical impulses produced by neurons. Brain cells communicate through a combination of chemical neurotransmitters and electrical gradients, and EEG captures these electrical changes. The signal detected by an EEG electrode represents a summation of the electrical activity from many neurons over a broad area of the cortex.
These channels measure the voltage differences between various points on the scalp. A single neuron’s electrical activity is too small to be detected by scalp EEG, so the recorded signal reflects the synchronized activity of at least 6 square centimeters of cortical tissue. Multiple channels are used to capture a broader and more detailed picture of electrical activity across different brain areas simultaneously. This allows for a more comprehensive brain activity measurement.
Mapping Brain Activity Through Channels
Strategic placement of EEG channels is important for mapping brain activity. The International 10-20 system is a standardized method for consistent electrode placement across individuals. This system uses anatomical landmarks, such as the nasion (bridge of the nose), inion (bump at the back of the head), and preauricular points (in front of the ears), to divide the skull into proportional distances. The “10” and “20” refer to distances between adjacent electrodes, which are either 10% or 20% of the total measured head distances.
Each electrode in the 10-20 system is identified by a letter and a number. The letter indicates the brain region underlying the electrode, such as F for frontal, T for temporal, C for central, P for parietal, and O for occipital. Odd numbers are used for electrodes on the left side of the head, even numbers for the right, and a “z” for midline electrodes. This systematic placement enables researchers and clinicians to localize where specific brain activity originates, providing insights into which brain regions are involved in particular functions or dysfunctions.
Interpreting Signals from EEG Channels
The “signals” recorded by EEG channels represent brainwaves, which are oscillations of electrical activity. These brainwaves are categorized into different frequency bands, each associated with distinct brain states. For instance, Delta waves, the slowest brainwaves, range from 0.5 to 4 Hz and are prominent during deep sleep and restorative processes. Theta waves, between 4 and 8 Hz, are associated with creativity, meditation, and memory consolidation, and often appear during REM sleep.
Alpha waves, ranging from 8 to 13 Hz, are observed during relaxed wakefulness and can promote a calm, alert state. Beta waves, with frequencies from 13 to 30 Hz, are present during active thinking, concentration, and alertness. Higher frequencies, known as Gamma waves (above 30 Hz), are associated with mental activities, problem-solving, and deep immersion in complex tasks. Analyzing how these brainwave patterns change across different channels provides insights into various brain functions or conditions, such as sleep disorders, epilepsy, or cognitive states.