Electroencephalography (EEG) is the recording of electrical activity of the brain, over a short period of time, usually 20-40 minutes, as recorded from multiple electrodes placed on the scalp. In neurology, the main diagnostic application of EEG is in the case of epilepsy, as epileptic activity can create clear abnormalities on a standard EEG study. A secondary clinical use of EEG is in the diagnosis of coma, encephalopathies, and brain death.
An electromyogram (EMG) is a test that is used to record the electrical activity of muscles. When muscles are active, they produce an electrical current. This current is usually proportional to the level of the muscle activity. An EMG is also referred to as a myogram.
EMG can be used to detect abnormal electrical activity of muscle that can occur in many diseases and conditions, including muscular dystrophy, inflammation of muscles, pinched nerves, peripheral nerve damage (damage to nerves in the arms and legs), amylotrophic lateral sclerosis (ALS), myasthenia gravis, disc herniation, and others.
A nerve conduction velocity test (NCV) is an electrical test that is used to determine the adequacy of the conduction of the nerve impulse as it courses down a nerve. This test is used to detect signs of nerve injury. In this test, the nerve is electrically stimulated, and the electrical impulse downstream from the stimulus is measured. This is usually done with surface patch electrodes (they are similar to those used for an electrocardiogram) that are placed on the skin over the nerve at various locations. One electrode stimulates the nerve with a very mild electrical impulse. The resulting electrical activity is recorded by the other electrodes. The distance between electrodes and the time it takes for electrical impulses to travel between electrodes are used to calculate the speed of impulse transmission (nerve conduction velocity). A decreased speed of transmission indicates nerve disease. A nerve conduction velocity test is often done at the same time as an electromyogram (EMG) in order to exclude or detect muscle conditions.
BERA (Brainstem evoked response audiometry), ABR (Auditory brain stem response), BAER (Brainstem auditory evoked response audiometry).
BERA is an electro-physiological test procedure which studies the electrical potential generated at the various levels of the auditory system starting from cochlea to cortex.
Visual Evoked Potential is used to detect lesions of the optic nerve, or inflammation of the optic nerve (optic neuritis), and also optic nerve demyelination as with demyelinating disease (Multiple Sclerosis).