An Electroencephalogram, commonly known as an EEG, is a medical test that measures the electrical activity of the brain. This procedure uses small sensors, called electrodes, placed on the scalp to detect the tiny electrical charges generated by brain cells. The primary purpose of an EEG is to record these electrical signals and display them as a visual representation, often referred to as an “EEG graph” or “brainwave patterns”. This graph provides a window into the continuous electrical processes occurring within the brain.
Understanding the Electroencephalogram
The electrical signals detected by an EEG originate from the communication between brain cells, specifically neurons. Neurons are electrically excitable cells that process and transmit information through electrical and chemical signals. These signals create electrical fields that can be picked up at the scalp.
During an EEG, multiple small metal discs, or electrodes, are attached to the scalp using a special paste or glue. These electrodes detect the subtle electrical charges produced by the brain cells. The detected charges are then amplified significantly, often up to 10,000 times, by the EEG machine. This amplified information is then converted into a visual output, appearing as wavy lines or traces on a computer screen or printed paper, which constitutes the EEG graph. This visual representation illustrates how well different areas of the brain are functioning by showing the patterns of electrical activity over time.
Decoding Brainwave Patterns
The EEG graph displays various brainwave patterns, which are categorized by their frequency, measured in Hertz (Hz), and reflect different states of consciousness or brain activity.
Delta waves are the slowest brainwaves, typically ranging from 0.5 to 4 Hz. They are most prominent during deep, dreamless sleep and indicate a state of profound relaxation and unconsciousness. The presence of delta waves during wakefulness can sometimes suggest brain dysfunction.
Theta waves fall within the 4 to 8 Hz range. These waves are often associated with states of drowsiness, light sleep, meditation, and deep relaxation. They can also appear during creative thinking or when experiencing strong emotions.
Alpha waves have a frequency of 8 to 13 Hz. These waves are characteristic of a relaxed, wakeful state, often observed when a person’s eyes are closed and they are at rest, but not yet asleep. When a person opens their eyes or engages in mental exertion, alpha activity tends to decrease, and faster brainwaves become more prominent.
Beta waves are faster, with frequencies between 13 and 30 Hz. They are typically present during active wakefulness, concentration, problem-solving, and alert mental activity. These waves reflect an engaged and attentive mind.
Gamma waves are the fastest brainwaves, generally ranging from 30 to over 100 Hz. These high-frequency oscillations are thought to be involved in higher-level cognitive functions, such as learning, memory formation, and conscious perception, and may indicate widespread brain activity working in unison.
How EEG Graphs Aid Diagnosis
EEG graphs aid medical professionals in diagnosing a range of neurological conditions. By analyzing the unique patterns and any abnormalities present in the brainwave activity, healthcare providers can gain insights into brain function.
One of the most common applications of EEG is in the diagnosis and monitoring of epilepsy. Seizure activity often manifests as rapid spiking waves or specific spike-and-wave complexes on the EEG graph, allowing doctors to identify the type of epilepsy and potential triggers. The continuous recording capability of EEG helps detect the onset and progression of seizures.
EEG is also used to evaluate:
Sleep disorders, such as sleep apnea, by identifying different sleep stages and abnormal sleep patterns.
The effects of brain injuries, including concussions, by revealing changes in normal brain activity.
Conditions like encephalitis, which involve brain inflammation, through characteristic slow wave patterns on the EEG.
The extent of brain damage in patients in a coma.
Blood flow during certain surgeries.
Interpreting Key Features
Understanding an EEG graph involves recognizing the difference between typical and atypical brain activity. Normal EEG patterns generally exhibit symmetry between the brain’s hemispheres and predictable amplitude ranges, typically varying between 20 and 100 microvolts, with frequencies between 1 and 30 Hz. The presence of a consistent background rhythm, such as the posterior alpha rhythm, is a common indicator of healthy brain function in a relaxed, awake state.
Deviations from these normal characteristics can signal underlying issues. The appearance of unusually slow waves during wakefulness may indicate brain dysfunction. Spikes or sharp waves are often associated with seizure activity. Asymmetry in brainwave patterns between the two sides of the brain, or sudden, unexpected changes in frequency or amplitude, can also point to neurological problems. While this overview provides a basic understanding of EEG graph features, a comprehensive interpretation requires extensive training and expertise from a qualified medical professional, who evaluates hundreds of pages or screens of activity, paying attention to the basic waveform, bursts of energy, and responses to stimuli.