ELECTROENCEPHALOGRAM Presented By: (Name Hidden) Calcutta University

What Is EEG? EEG refers to the recording of the brain's spontaneous electrical activity over a short period of time, usually 20–40 minutes, as recorded from multiple electrodes placed on the scalp. EEG generally focuses on the spectral content i.e., the type of neural oscillations that can be observed in EEG signals. When the neurons of the human brain process information, they do so by changing the flow of electrical impulses across their membranes. These changing currents generate electric and magnetic fields that can be recorded from the surface of the scalp. The electric fields are measured by attaching small electrodes to the scalp. The potentials between different electrodes are then amplified and recorded as the Electroencephalogram (EEG).

A Brief History In 1912, Russian physiologist, Vladimir Vladimirovich Pravdich-Neminsky published the first animal EEG and the evoked potential of the mammalian (dog). In 1914, Napoleon Cybulski and Jelenska-Macieszyna photographed EEG-recordings of experimentally induced seizures. Then in 1924 German physiologist and psychiatrist Hans Berger invented the electroencephalogram (giving the device its name) and recorded the first human EEG. This invention was described as "one of the most surprising, remarkable, and momentous developments in the history of clinical neurology". Berger’s subjects revealed robust changes when the eyes were closed and when the subjects performed mental arithmetic. The scientific community was at first quite skeptical that these scalp signals originated in brain tissue but by 1934 their brain origins had been established.

When An EEG Is used? Epilepsy (a condition that causes repeated brain seizures). Brain infections, such as encephalitis. Loss of ability in thinking, judgement (Dementia). Head injuries. Brain tumours. Bleeding on the brain (Haemorrhage). Brain dysfunction that may have a variety of causes (Encephalopathy). Inflammation of the brain (Encephalitis). Stroke. Sleep disorders, such as Narcolepsy and Insomnia. Abnormal changes in body chemistry that affect the brain. Brain diseases such as Alzheimer's disease. Investigate periods of unconsciousness. Monitor the brain during brain surgery. EEG is sometimes used to determine the level of brain function in people who is in a coma. An EEG is also used to determine brain death. It may be used to prove that someone on life-support equipment has no chance of recovery.

Types of EEG Routine EEG  This is the basic EEG test that is most often used to diagnose epilepsy and other neurological conditions. It provides a 20 to 40 minute sample of brain activity. Ambulatory EEG  If the sample of brain activity gathered from the routine EEG isn't enough, an ambulatory EEG may be recommended to capture more activity and give a better idea of when seizures occur. This EEG can capture as much as 72 hours worth of brain activity, which is recorded while you go about your normal daily activities outside the doctor's office. Video EEG  Video EEG uses a regular EEG machine, but adds video monitoring. This allows doctors to view electrical activity in the brain and a person's physical activity, and make a comparison between the two. Special electrode EEG  Sometimes, an EEG needs to be performed using different electrodes to get a better reading. These electrodes may be inserted directly into the brain via tiny holes that are drilled into the skull to measure activity deep inside the brain. Brain mapping, a fairly new method that is very similar to EEG. With electrodes placed on the person's scalp to transmit the brain's electrical activity, a computer makes a color-coded map of signals from the brain. It is sometimes done to find a specific problem area in the brain that has already shown up on a regular EEG. Doctors are still not certain how brain mapping could be best used.

Is There Any Risk Associated With EEG? Very few risks are associated with an EEG. The patient may be asked not to take certain seizure or antidepressant medications 1 to 2 days before having an EEG. This may make the person more prone to having a seizure, which is exactly what the doctor would like to measure. During an EEG, the doctor may encourage the things that stimulate seizures, such as deep breathing or flashing lights, so that he or she can see what happens in the brain during the seizures. But overall, an electroencephalogram (EEG) is a safe test. The electrical activity of brain is recorded, but at no time is any electrical current put into a subject's body. An EEG should not be confused with electroshock (electroconvulsive) therapy.

How To Prepare For EEG? If the patient routinely takes seizure medication to prevent seizures, antidepressants, or stimulants, he or she may be asked to stop taking these medications 1 to 2 days before the test. The patient should wash his / her hair in the morning or the night prior to the test and should avoid using hair styling products (oil, conditioner, hair cream, hairspray or gel) on the day of the exam. It is prudent to have someone take the patient to the EEG location, especially if he or she has been asked to stop taking seizure medications. The patient may be told not to consume caffeine before the test. If the patient is having a sleep EEG, he or she may be asked to stay awake the night before the exam.

What Happens During The Test? Patient will be asked to lie on back on a bed or in a reclining chair with eyes open at initial stage. Flat metal disks called electrodes are placed all over the scalp. The disks are held in place with a sticky paste. The electrodes are connected by wires to a speaker and recording machine. Patient may be asked to breathe deeply and rapidly or to stare at a flashing light -- both of these activities produce changes in the brain-wave patterns. If the patient is being evaluated for a sleep disorder, EEG may be performed continuously during the night in a asleep state. In case of Video EEG, body motions are captured by a video camera while the EEG simultaneously records patient's brain waves during a seizure. The recording machine changes the electrical signals into patterns that can be seen on a computer. It looks like a bunch of wavy lines.

Types of Brain Waves Delta wave. Frequency range up to 4 Hz Theta wave. Frequency range 4 Hz to 7 Hz Alpha wave. Frequency range 8 Hz to 12 Hz Beta wave. Frequency range 12 Hz to 30 Hz Sensorimotor or Mu rhythm. Frequency range 8 to13 Hz Gamma wave. Frequency range 30 Hz to 100 Hz

Possible Normal Results In adults who are awake, the EEG shows mostly alpha waves and beta waves. The two sides of the brain show similar patterns of electrical activity. There are no abnormal bursts of electrical activity and no slow brain waves on the EEG tracing. If flashing lights (photic stimulation) are used during the test, one area of the brain (the occipital region) may have a brief response after each Flash of light, but the brain waves are normal.

Possible Abnormal Results The two sides of the brain show different patterns of electrical activity. This may mean a problem in one area or side of the brain is present. The EEG shows sudden bursts of electrical activity (spikes) or sudden slowing of brain waves in the brain. These changes may be caused by a brain tumor, infection, injury, stroke, or epilepsy. The EEG records changes in the brain waves that may not be in just one area of the brain. A problem affecting the entire brain-such as drug intoxication, infections (encephalitis), or metabolic disorders. The EEG shows delta waves or too many theta waves in adults who are awake. These results may mean brain injury or a brain illness is present. Some medicines can also cause this. The EEG shows no electrical activity in the brain (a "flat" or "straight-line" EEG). This means that brain function has stopped, which is usually caused by lack of oxygen or blood flow inside the brain.