Electroenecephalogram (EEG) After Head Trauma

The EEG tracks brain waves

Nerve cells in the brain communicate with each other through electrical signals. After a traumatic brain injury these electrical signals may flow in different patterns, be blocked, or no longer exist. Signs of altered electrical activity in the brain include the development of seizures, confusion, difficulty recalling and expressing information, or problems sleeping.

One test to determine what is going on with the brain’s electrical activity is an electroencephalogram, or EEG.

The EEG picks up the electrical signals in the brain and tracks how they flow between different areas of the brain. The EEG also measures the level of activity in specific areas of the brain.

How Is the Test Performed?

An EEG is non-invasive, which means nothing needs to be inserted into the body. Instead, thin electrodes are attached to the scalp with an adhesive gel. The electrodes are able to pick up and record the electrical activity inside the brain. It’s the same concept as an EKG that measures the electrical activity of the heart, except many more electrodes are used so that the entire brain’s activity can be tracked.

When the EEG measures activity it records them as waves. These waves are created by synchronized electrical impulses that flow through tracts of neurons as they send information. The activity can be observed by recording the waves on a sheet of paper and further classifying them by how wide and fast the waves move.

The standard measure for brain waves is Hertz per second. The brain waves change based on what we are doing. Below is the scale commonly used by neurologists that classifies brainwaves from the fastest, to slowest brainwaves:

  • Gamma Waves: >30 hz/second and higher. They are observed when actively thinking, processing memory and using language. They are also present when a person experiences feelings of universal love and altruism.
  • Beta Waves: 13-30 hz/second: This is the brainwave pattern most people are in throughout the day when performing normal activities.
  • Alpha Waves: 8-13 hz/second. This brain wave is often seen in the posterior areas of the brain when patients are awake, with eyes closed in a relaxed state.
  • Theta Waves: 4-8 hz/second. This is the brain wave pattern of deep relaxation or light sleep.
  • Delta Waves:0.4 hz/second. Brain activity slows profoundly during deep sleep, as demonstrated by delta waves. This is the dreamless, completely unconscious sleep state.

EEG Result After Head Trauma

After a traumatic brain injury, the EEG may show both Delta and Theta  waves while  patients are awake, and that is not normal, since Delta waves should only be present during sleep. These slow waves may involve the entire brain or be specific to a certain region.

What this tells the neurologist is that something has altered the way electrical impulses pass through the brain’s nerve cells. After an injury this could be torn tissues, scars, inflammation, or blood clots.

Quantitative Measurements

When the data is used to better understand what is happening to the brain, it is called a Quantitative Electroencephalogram, or qEEG.

The qEEG explores various characteristics of the waveforms including symmetry, power, frequency, amplitude and coherence. These characteristics can be analyzed together, or independently. Depending on the behavior of the brain’s waveforms and energy, medical specialists can better understand traumatic brain injuries and the likelihood of longer-term complications developing.

The EEG and TBI Seizures

In patients with TBI and seizure disorder, the EEG can show intermittent abnormal brain waves, called spike or sharp waves. They tend to occur in the area of the brain where most of the damage occurred.

Sometimes, the EEG can be normal in between the spells and an attempt is usually made to record a seizure during an EEG monitoring, so that the activity and area of the brain sending out abnormal impulses can be studied. What is most often recorded during a seizure-EEG is that the brain waves are different from their baseline

The most important part of testing brain waves, is ensuring that a specialist trained in understanding head injury, seizure and EEGs reads and communicates the information.


Sick, J., Bray, E., Bregy, A., Dietrich, W. D., Bramlett, H. M., & Sick, T. (2013). EEGgui: a program used to detect electroencephalogram anomalies after traumatic brain injury. Source Code For Biology & Medicine, 8(1), 1-7. doi:10.1186/1751-0473-8-12

Traumatic brain injury and epilepsy: Underlying mechanisms leading to seizure. (2015). Seizure, 3313-23 11p. doi:10.1016/j.seizure.2015.10.002

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