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Electroencephalograms (EEG)

By Sucharita Desu

Neurons have a fascinating way of communicating with each other and muscles throughout the body. They use electrochemical signals to pass on instructions and messages, allowing you to move, think and function the way you do. The electric part of the signal is an electric current, while the chemical part is a neurotransmitter. Stimulating a neuron causes electric action potential that starts at the dendrites, travels along the axon, and to the next cell. The cell that receives the electric impulse can either be another neuron, a muscle cell, or a gland cell. At the axon terminal, the electric current triggers the release of neurotransmitters as messages into the synapse. These chemicals will bind to receptors on the next cell and continue the signal, or act on it. The type of communication and the speed of the responses to an action potential depends on several factors, including the speed and size of the electric impulse, and the duration of the signal.

An electroencephalogram (EEG) is a neuroimaging device used to measure and record the brain’s electrical activity (i.e., the electric signals it produces). An EEG consists of electrodes in the form of small discs that are attached to your scalp. These electrodes are then connected to another machine using wires to provide and display information about the brain’s activity. More specifically, the EEG will sense and amplify the electrical impulses your neurons use to communicate, and then display and record your brain wave patterns. There are various patterns that are unique to specific physical states, such as when you are sleeping, awake, and having a seizure. During an EEG, you may be asked to perform cognitive or engaging tasks, such as opening and closing your eyes, doing some mathematical calculations, reading a paragraph, looking at a picture, breathing deeply, looking at a flashlight, and more.

EEGs are typically used to help diagnose and monitor medical conditions that may affect the brain. Most of the time, it is used as a diagnostic test for epilepsy as well as to check seizure activity. They may also be used to monitor, diagnose, or treat Alzheimer’s disease, dementia, brain injury, encephalitis, to find certain symptoms (e.g., confusion, fainting and memory loss), as well as to monitor brain activity during surgeries and during comatose. Furthermore, they may be useful in diagnosing or treating brain dysfunction, such as encephalopathy, and Creutzfeldt-Jakob disease. It may also be used to confirm brain death in someone who has been in a coma for a long time.

There are multiple types of EEGs depending on their purpose. Some might be routine, especially for those with epilepsy. Others may be prolonged to gather more information. These EEGs are typically used to diagnose and manage seizure disorders. Continuous EEGs may be used to find the right level of anesthesia required for a patient that is in a medically induced coma. Ambulatory EEGs are much smaller in size and are sent home with the patient to record brain wave patterns as they complete everyday tasks. This type of EEG is not always suitable, as it is not good at differentiating between epileptic and nonepileptic seizures. Some EEGs may be performed while you sleep in case a typical routine EEG did not provide enough data or to test for sleep disorders. In this case, you may be asked to avoid sleeping as much or at all the night before. Lastly, EEGs may be accompanied with a video recording to help see and hear what the patient is doing during any brain events, like seizures.

EEGs are meant to be safe and painless, meaning you should feel little to no discomfort during it. The electrodes do not transmit any sensations, they are only used for recording activity. Like any other test, be sure to consult your medical professional about any precautions to take prior to, during and after an EEG. Usually, however, the side effects are slight feelings of dizziness and a possible risk of a seizure. One thing to note, is that depending on the purpose of the EEG, a seizure may be intentionally triggered during the test, especially for epileptic patients, however there will be sufficient medical care present if needed. Finally, a general tip to get you prepared may be to wash your hair before the test to allow the electrodes to stick to your head as securely as possible.

Results are typically interpreted by a doctor or healthcare provider specialized in reading and understanding EEGs. They will review the brain wave patterns that the EEG records and describe it as either normal or abnormal. Abnormal patterns in brain activity can have a wide range of causes, such as alcoholism, drug abuse, brain/head injury (i.e., bleeding and/or swelling), brain tumors, migraines, seizure disorders, sleep disorders, and stroke. In the case of an abnormal result, the patient may also be directed to a neurologist or another specialist to diagnose, treat and manage their condition.

This article merely grazes the surface of the technology and use of an electroencephalogram. To learn more in depth about EEGs, please check out the following resources: 

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