Electroencephalography (EEG) is a non-invasive method to record the electrical activity of the brain based on electrodes located on the scalp. EEG measures voltage fluctuations resulting from ionic current within the neurons of the brain. The electrical signal captured by the EEG electrodes represent the macroscopic activity of the upper surface layers of the brain. However, the electric potential generated by an individual neuron is far too small to be picked up by EEG. Therefore, EEG activity reflects the summation of the synchronous activity of millions of neurons. Importantly, because voltage field gradients fall off with the square of distance, activity from deep sources is more difficult to detect than currents near the skull.

For diagnosing epilepsy, the EEG signal is analyzed in the frequency domain, which identifies the neural oscillations or "brain waves" that are related to normal vs. abnormal brain activity. EEG is an extremely valuable tool for research and diagnosis. It is one of the few mobile techniques available and offers millisecond-range temporal resolution, which is not possible with other brain imaging techniques such as CT, PET or MRI.

EEG activity in the frequency domain is usually represented by oscillations at specific frequency ranges (bands). Historically, these frequency bands have been associated with different cognitive, emotional, and behavioral states of brain functioning (e.g., walking, paying attention, remembering, and the classical sleep stages). These frequency oscillations represent synchronized activity over a network of neurons.

EEG was developed by the German physiologist and psychiatrist Hans Berger, which recorded the first human EEG in 1924. In 1934, Fisher and Lowenbach first demonstrated epileptiform spikes using EEG. In 1935, Gibbs, Davis, and Lennox described interictal spike waves and the three cycles/s pattern of clinical absence seizures, which opened the field of clinical EEG. Subsequently, in 1936 Gibbs and Jasper reported the interictal spike as the focal signature of epilepsy.

Epilepsy monitoring is typically done to distinguish epileptic seizures from other types of abnormalities and diseases, such as psychogenic non-epileptic seizures, fainting, sub-cortical movement disorders and migraine variants. It is also used to characterize seizures for the purposes of treatment, and to localize the brain region from which a seizure originates.

In conventional clinical grade scalp EEG, the recording is obtained by placing electrodes on the scalp with a conductive gel or paste (i.e. wet electrodes). Each of the electrodes is connected to a wire that transmits the signal into an amplifier and then to a recording and analysis software. The gel is used in order to improve the quality of the signal and reduce the signal to noise ratio.

The standard use of EEG headsets with multiple wet electrodes has several disadvantages. First and foremost, the setup time is very long (around 30 minutes of preparation). Moreover, patients are required to have their hair and scalp covered in uncomfortable gel, which requires a hair wash to remove. The setup requires trained staff, which reduces the efficiency of measuring EEG at home and hence, using EEG outside the hospital or laboratory settings can be very cumbersome. Additionally, the performance and signal quality of wet electrodes degrades after several hours. Lastly, these clinical grade systems are usually non-mobile, hence preventing their use in locations outside the hospital or research lab.

In the last 30 years, there has been an explosion of new EEG headsets. Headsets that use dry electrodes (no gel needed), only a few electrodes (1-8), and are wireless and mobile. Importantly, the electronics of the dry electrodes have improved substantially, and hence now the signal quality and signal to noise ratio of the dry electrodes are almost as good as the clinically grade wet electrodes. Importantly, with this improved signal, we can now use these mobile dry electrodes EEG headsets out in the world, at home, and in any other regular activity people do, such as walking, working in front of a computer, watching TV, etc. However, these dry electrodes do not perform well when the mechanical contact is not very strong. Hence, most of these systems have a poor signal and extra noise in scalp areas that have hair. The best signal originates in non-hair scalp areas, especially the forehead. Therefore, the main challenge for using mobile, wireless, dry electrode EEG systems is to be able to decode and extract meaningful clinical-relevant EEG data from the forehead alone.

Epilepsy is not a unified condition but rather a spectrum of conditions with a wide range of seizure types, origins, and control, which vary from person-to-person. Epilepsy is a neurological chronic disorder that affects the nervous system. It is usually diagnosed after a person has had at least two seizures (or after one seizure with a high risk for more) that were not caused by some known medical condition. Epilepsy is characterized by recurrent, unpredictable, and unprovoked seizures, which and can cause other health problems. Many people with epilepsy have more than one type of seizure and may have other symptoms of neurological problems as well.

Seizures are caused by disturbances or a sudden surge in the electrical activity of the brain. This sudden surge is caused by an imbalance between excitation and inhibition in the brain. A seizure usually affects how a person appears or acts for a short time. The seizures in epilepsy may be related to a brain injury, genetics, immune, brain structure or metabolic cause, but most of the time the cause is unknown. The location of the seizure in the brain, how it spreads, how much of the brain is affected, and how long it lasts all have profound effects. These factors determine the character of a seizure and its impact on the individual. Seizures can take on many different forms, and seizures affect different people in different ways. Seizures are not a disease in themselves. Instead, they are a symptom of many different disorders that can affect the brain. Some seizures can hardly be noticed, while others are totally disabling.

A typical seizure usually has three phases. An aura or warning is the first symptom of a seizure and is considered as the first part of the seizure. Importantly, however, most people do not feel an aura and hence are surprised by the seizure onset. The middle of a seizure is called the ictal phase where the major electrical “storm” of activity in the brain occurs. After the end of the seizure, there is the postictal phase, which is the recovery period after the seizure. Some people recover immediately while others may take minutes to hours to feel like their usual self.

Having seizures and epilepsy affect one's safety, well-being, relationships, work opportunities and success, the ability to drive, run, and swim, sleep quality, and almost every aspect of life. Most seizures end on their own and cause minimal concerns. However, during seizures, people can injure themselves, develop other medical problems or life-threatening emergencies. The overall risk of dying for a person with epilepsy is 1.6 to 3 times higher than for the general population. Sudden unexpected death in epilepsy (SUDEP) is the most common disease-related cause of death in epilepsy. Overall, the chance of an injury is higher for people with uncontrolled seizures. Some common injuries may include bruises, cuts, burns, and falls. More serious problems, such as broken bones, concussions, head injuryes, or breathing problems, usually are seen in people who have generalized seizures with falls, long seizures, or repeated or clusters of seizures.

People living with epilepsy face higher frequency of depression and other mood disorders. They suffer from social isolation, have challenges in school and if they want to live independently. People with epilepsy have higher unemployment rates, limitations on driving, and higher risk of early death. Due to all the above problems and challenges, the socioeconomic burden on people with epilepsy is very high.

Epilepsy is the fourth most common neurological disorder and affects people of all ages. According to the Centers for Disease Control and Prevention (2015), the number of people living with epilepsy in the United States is an an all-time high. Here are a few facts about epilepsy (taken from the Epilepsy foundation): 65 MILLION people around the world have epilepsy (other sources estimate that this could be as high as 100 million) 3.4 MILLION people in the United States have epilepsy. 1 IN 26 people in the United States will develop epilepsy at some point in their lifetime. 150,000 new cases of epilepsy in the United States each year. 30% of people with epilepsy live with uncontrollable seizures because existing medications do not work for them. That is more than 1 million people in the US. The cause for the disorder for 6 OUT OF 10 people with epilepsy is unknown. New cases of epilepsy are most common among children, mainly in the first year of life. The rate of new cases of epilepsy gradually decreases until age 10 and then stabilizes. After age 55, the rate of new cases of epilepsy starts to increase again, as people develop strokes, brain tumors, or Alzheimer's disease, which all can cause epilepsy.