100 Years of Electroencephalography (EEG) in Human Medicine

Electroencephalography (EEG) is a remarkable technique that allows us to peek into the human brain without having to break open the skull. This incredible innovation has been around for 100 years, and its significance cannot be overstated. In this article, we will delve into the history of EEG, its working, and its applications in medicine.

The Birth of EEG

The journey of EEG began with the work of German physiologist Hans Berger, who recorded the first human EEG in 1924. However, the concept of electrical activity in the brain dates back to the late 19th century. British physician Richard Caton discovered electrical activity in the brains of monkeys and rabbits in 1875, while Polish scientist Adolf Beck found fluctuating activity in the brains of dogs and rabbits when stimulating their senses in 1890. Vladimir Pravdich-Neminsky took it a step further by recording the first mammalian EEG in a dog’s brain in 1912. Berger’s contribution was to invent the EEG, name it, and introduce it in clinical settings.

What is EEG?

EEG is a non-invasive test that measures electrical activity in the brain. The term “electroencephalography” is derived from “electro-” (relating to electricity), “-encephalo-” (referring to the brain), and “-graphy” (meaning to show or represent). Neurons in the brain generate electrical activity by moving charged particles, which can be visualized using an EEG test. Researchers can relate this data to different levels and modes of brain activity, distinguishing between normal and abnormal states.

Applications of EEG

EEG is a common diagnostic test in clinical settings, used to diagnose conditions such as epilepsy, anaesthesia, sleeping patterns, neurological activity during a coma, and availability of oxygen. It can also help confirm brain death, one of the two legally recognized forms of death in India. In research, EEG is used in neuroscience, cognitive psychology, neurolinguistics, and neuromarketing studies, as well as to develop brain-computer interfaces.

Volume Conduction

During an EEG test, electrodes are placed on the scalp to measure electrical activity in the brain. However, there are many layers of skin, fluid, and bone between the electrodes and the neurons. When a neuron produces electrical activity, charged particles move through these media, reflected, refracted, and scattered before reaching the electrodes. This is known as volume conduction. The raw data collected by the electrodes needs to be corrected for the effects of volume conduction and noise in the data.

How an EEG Test Works

The human brain is constantly exchanging atoms, molecules, and proteins with its surroundings. When a large number of neurons start exchanging ions at the same time, a wave of electrical activity flows through the brain. The electrodes on the scalp track the changes in voltage as these waves move past them, creating an electroencephalogram.

Placing Electrodes

Electrodes can be placed anywhere, but following the International 10-20 System is recommended for consistency. This system ensures that the distance between electrodes is either 10% or 20% of the total distance between two points on the head. Four common points of reference are the nasion, inion, tragus, and the crest at the back of the skull.

What EEG Shows and Doesn’t Show

The changes in voltage recorded by the electrodes are transmitted to a computer, which plots the readings on a graph. Health workers are interested in the voltage and frequency of the variations. EEG is better at tracking rapid electrical activity in the brain, but it is biased towards signals generated closer to the surface of the cortex. To overcome these limitations, researchers use EEG with other tests, like MRI, and develop sophisticated data acquisition and processing methods.

Affordability of EEG

Aside from its diagnostic abilities, an EEG setup is relatively simple and cost-effective. The equipment doesn’t take up much space, doesn’t emit radiation or sounds, and is non-invasive and portable. However, setting up an EEG test requires time and attention to detail, and the readings can be affected by factors like thicker hair.

In conclusion, EEG is a remarkable technique that has come a long way since its inception 100 years ago. Its applications in medicine are vast, and its simplicity and cost-effectiveness make it an essential tool in many clinical settings. As we continue to advance our understanding of the human brain, EEG will remain a crucial part of our diagnostic arsenal.

Historical Context:

• 1875: British physician Richard Caton discovers electrical activity in the brains of monkeys and rabbits.
• 1890: Polish scientist Adolf Beck finds fluctuating activity in the brains of dogs and rabbits when stimulating their senses.
• 1912: Vladimir Pravdich-Neminsky records the first mammalian EEG in a dog’s brain.
• 1924: German physiologist Hans Berger records the first human EEG and introduces it in clinical settings.

Summary in Bullet Points:

• EEG is a non-invasive test that measures electrical activity in the brain, allowing researchers to visualize and relate data to different levels and modes of brain activity. • The term “electroencephalography” is derived from “electro-” (relating to electricity), “-encephalo-” (referring to the brain), and “-graphy” (meaning to show or represent). • EEG is used to diagnose conditions such as epilepsy, anaesthesia, sleeping patterns, neurological activity during a coma, and availability of oxygen. • It can also help confirm brain death and is used in research, neuroscience, cognitive psychology, neurolinguistics, and neuromarketing studies. • The test works by placing electrodes on the scalp to measure electrical activity in the brain, which is affected by volume conduction and noise in the data. • The International 10-20 System is recommended for placing electrodes for consistency. • EEG is better at tracking rapid electrical activity in the brain, but is biased towards signals generated closer to the surface of the cortex. • The test is relatively simple and cost-effective, but requires time and attention to detail, and readings can be affected by factors like thicker hair. • EEG has been around for 100 years and has come a long way since its inception, with its applications in medicine being vast and essential in many clinical settings.