An electrogram (EGM) is a recording of electrical activity of organs such as the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

and

heart The heart is a muscular Organ (biology), organ found in humans and other animals. This organ pumps blood through the blood vessels. The heart and blood vessels together make the circulatory system. The pumped blood carries oxygen and nutrie ...

, measured by monitoring changes in

electric potential Electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as electric potential energy per unit of electric charge. More precisely, electric potential is the amount of work (physic ...

. Historically, it also referred to an instrument to measure atmospheric electrical potential.

Brain

Electroencephalography (EEG)

An electroencephalogram (EEG) is an electrical recording of the activity of the brain taken from the

scalp The scalp is the area of the head where head hair grows. It is made up of skin, layers of connective and fibrous tissues, and the membrane of the skull. Anatomically, the scalp is part of the epicranium, a collection of structures covering th ...

. An EEG can be used to diagnose

seizures A seizure is a sudden, brief disruption of brain activity caused by abnormal, excessive, or synchronous neuronal firing. Depending on the regions of the brain involved, seizures can lead to changes in movement, sensation, behavior, awareness, o ...

, sleep disorders, and for monitoring of level of anesthesia during surgery.

Electrocorticography (ECoG or iEEG)

An electrocorticogram is an electrical recording of the brain measured intracranially, that is, from within the brain.

Eye

Electrooculography (EOG)

An electrooculogram (EOG) is an electrical recording of the potential between the

cornea The cornea is the transparency (optics), transparent front part of the eyeball which covers the Iris (anatomy), iris, pupil, and Anterior chamber of eyeball, anterior chamber. Along with the anterior chamber and Lens (anatomy), lens, the cornea ...

and the

retina The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...

, and does not change with visual stimuli. An EOG can measure movements of the eyes and can help in diagnosis of nystagmus.

Electroretinography (ERG)

An electroretinogram (ERG) is an electrical recording of the electrical activity of the retina.

Heart

Electrocardiogram (ECG)

An electrocardiogram (ECG or EKG) is an electrical recording of the activity of the heart. The typical meaning of an "ECG" is the 12-lead ECG that uses 10 wires or electrodes to record the signal across the chest. Interpretation of an ECG is the basis of a number of cardiac diseases including

myocardial infarction A myocardial infarction (MI), commonly known as a heart attack, occurs when Ischemia, blood flow decreases or stops in one of the coronary arteries of the heart, causing infarction (tissue death) to the heart muscle. The most common symptom ...

(heart attack) and arrhythmias such as

atrial fibrillation Atrial fibrillation (AF, AFib or A-fib) is an Heart arrhythmia, abnormal heart rhythm (arrhythmia) characterized by fibrillation, rapid and irregular beating of the Atrium (heart), atrial chambers of the heart. It often begins as short periods ...

Cardiac electrogram

When electrical recordings are made from the

skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other animal coverings, such as the arthropod exoskeleton, have different ...

, it is considered to be an ECG as described above. However, electrical recordings made from within the heart such as with an artificial cardiac pacemaker or during an electrophysiology study, the signals recorded are considered an "electrogram" instead of an ECG. These signals are not interpreted in the same manner as an ECG.

Other muscles

An electromyogram (EMG) is an electrical recording of the activity of a

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

or muscle group. An EMG study can be combined with a nerve conduction study to diagnose neuromuscular diseases such as

peripheral neuropathy Peripheral neuropathy, often shortened to neuropathy, refers to damage or disease affecting the nerves. Damage to nerves may impair sensation, movement, gland function, and/or organ function depending on which nerve fibers are affected. Neuropa ...

and

amyotrophic lateral sclerosis Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) or—in the United States—Lou Gehrig's disease (LGD), is a rare, Terminal illness, terminal neurodegenerative disease, neurodegenerative disorder that results i ...