An electroencephalogram (EEG) study is a non-invasive method used to examine the electrical activity of the brain. This process allows for the observation of brain function, providing insights into its operational status. The primary purpose is to capture the faint electrical signals that brain cells, or neurons, use to communicate with one another. By analyzing the patterns of electrical activity, professionals can understand cognitive functions and identify certain medical conditions.
Fundamentals of EEG Recording
Electroencephalography measures the electrical impulses that result from the synchronized activity of large groups of neurons in the brain’s cortex. These signals, often called brainwaves, are detected by small metal discs known as electrodes. The electrodes do not transmit any electricity into the brain; they act as sensors to pick up the small electrical charges produced by brain cell communication. These charges are faint, measured in microvolts, or millionths of a volt.
To capture these signals, a technician first measures the individual’s head to ensure precise placement of the electrodes according to a standardized method like the International 10-20 system. Between 16 and 25 electrodes are attached to the scalp using a special conductive paste or an elastic cap with pre-positioned electrodes.
Once attached, wires connect the electrodes to an amplifier. This device strengthens the weak electrical signals from the brain, making them substantial enough to be recorded. A computer then digitizes these signals and displays them as a series of wavy lines, which represent the fluctuating brain activity over time.
Conducting an EEG Study
An EEG recording becomes a study when it is structured to investigate a particular question about brain function. The design of the study depends on its specific goal, which could range from diagnosing a medical condition to understanding cognitive processes. This involves more than just passively recording brainwaves; it often requires creating specific conditions or tasks for the participant.
A common approach is the resting-state EEG, where brain activity is recorded while the participant sits quietly with their eyes closed to establish a baseline of brain function. In contrast, task-based studies require participants to engage in specific activities, such as solving problems or viewing images. These tasks are designed to provoke brain activity related to functions like memory, attention, or emotional response.
Another method involves measuring event-related potentials (ERPs). In an ERP study, the participant is presented with a specific stimulus, like a light flash, many times. Researchers then average the EEG signals immediately following each stimulus. This process isolates the brain’s direct response to the event from background electrical noise. Participant preparation for any EEG study is straightforward, requiring clean, dry hair and avoiding stimulants like caffeine beforehand.
Making Sense of Brainwave Data
The data collected during an EEG study appears as a series of waveforms, which are analyzed based on their frequency, amplitude, and shape. Frequency, measured in Hertz (Hz), refers to the number of waves per second and is the most common way to categorize brainwaves. These frequencies are grouped into bands, each associated with different mental states.
- Delta waves (0.5-4 Hz) are the slowest and are seen during deep, dreamless sleep.
- Theta waves (4-8 Hz) are linked to drowsiness, light sleep, and states of deep relaxation.
- Alpha waves (8-13 Hz) are prominent when a person is relaxed and awake with their eyes closed.
- Beta waves (13-30 Hz) are faster and are associated with active thinking, concentration, and alertness.
- Gamma waves (above 30 Hz) are the fastest and are thought to be involved in higher-level information processing.
Analysis of ERPs focuses on specific voltage peaks and troughs that are time-locked to a stimulus. These components are labeled based on their electrical polarity (Positive or Negative) and their timing in milliseconds after the stimulus, such as the P300 component. The timing and strength of these ERPs provide precise information about the speed and engagement of cognitive processes.
Applications of EEG Studies
EEG studies have a wide array of applications in both clinical practice and scientific research. Some of the most common applications include:
- Diagnosing and managing epilepsy by detecting abnormal electrical discharges, such as spikes or sharp waves, that are characteristic of seizure activity.
- Investigating sleep disorders like sleep apnea by identifying the different stages of sleep.
- Evaluating other conditions such as brain tumors, head injuries, and brain inflammation.
- Studying the neural underpinnings of mental processes like attention, memory formation, and language processing with millisecond-level precision in cognitive neuroscience.
- Identifying differences in brainwave patterns in neurodevelopmental conditions like ADHD and autism spectrum disorder (ASD), which may serve as biomarkers.
- Powering brain-computer interfaces (BCIs), which use EEG signals to allow individuals with severe motor impairments to control external devices with their thoughts.