The History of Ambulatory EEG

Published 1/29/2025

Neurotech Historical Illustration of Brain

Ambulatory electroencephalography (aEEG) represents a groundbreaking evolution in neurophysiology. Its development shows the intersection of technological innovation, clinical necessity, and a drive to improve patient outcomes. It begins with a standard EEG and a need for monitoring epileptic activity in natural environments. Understanding the history of ambulatory EEG will give you a glimpse of how technological barriers were overcome. This guide will walk you through the timeline of advancements in ambulatory EEG.

The Discovery of Brain Electrical Activity

The history of standard EEGs dates to the late 19th century. A man named Richard Caton observed electrical activity in the brains of animals. Fast forward to 1924, Hans Berger recorded the first human EEG; this set the stage for innovation in EEG monitoring companies.

By the mid-20th century, EEG technology evolved into a popular machine called the Grass Model 8. This was a pen-writing machine with eight channels, and it became the standard in neurophysiology during the 1970s. The analog device delivered good results but lacked portability. Patients may feel less comfortable in a hospital environment versus national conditions like at home.

The Birth of Ambulatory EEG

As more patients required long-term monitoring, the demand for ambulatory EEGs increased. This is because in-hospital EEGs do not easily capture seizures outside controlled settings. This prompted EEG monitoring companies to innovate. Thus, a 1953 invention of ambulatory ECG was revisited by neurologists. Norman Holter, who was the inventor, was to perform cardiac monitoring with his machine. In order to replicate something for brain activity, you would need more channels and higher signal amplification.

There were a few products that laid the groundwork for what ultimately became the first Ambulatory EEG. In the early 1970s, Marson and McKinnon's recorders were used because of their ability to extend the recording duration. Next, in 1978, Quy developed a preamplifier chip that could be mounted on the scalp. This advancement improved signal quality and ignited the innovation of Ambulatory EEGs.

The Oxford Medilog

Oxford Instruments was founded in 1959 by Sir Martin Wood. Their experience in cryogenic technology propelled them into developing medical devices. This is where many EEG monitoring companies saw a growing demand for portable EEG systems. After working with neurologists and engineers, the Medilog 4-24 system emerged. Below are some of the key features that set this system apart from earlier EEG devices.

  • Compact Design: At just 1.5 pounds, the medilog was lightweight and portable.
  • Four-Channel Recording: Down from the typical 8-channel EEGs, the Medilog system used four channels with targeted areas.
  • Preamplifier Technology: Scalp-mounted preamplifiers ensured higher signal quality.
  • Video Playback: Medilog's system allowed clinicians to review 24 hours of EEG data in 24 minutes, drastically reducing analysis time.

Despite the revolutionary EEG device, the Oxford Medilog faced resistance from neurologists, who used the 8-channel Grass Model EEG. Researchers Rob Leroy and JS Ebersole studied the system's effectiveness and came to the conclusion that the Medilog was able to deliver meaningful results that could outperform stationary EEG studies.

The Eight-Channel Medilog 9000

To address the channel count concerns, Medilog expanded its product line in the 1980s. This new EEG has 8-channel recording capabilities and stereo EEG playback. The stereo playback allows enhanced seizure detection because clinicians were able to listen to the left and right hemispheres simultaneously. The Medilog 9000 further cemented Oxford Instruments as the leader in early ambulatory EEG technology.

Ambulatory EEG Impact on Neurological Diagnostics

The Oxford Medilog revolutionized ambulatory EEG by making long-term monitoring accessible. This made EEG monitoring cost-effective, patients were able to undergo testing in their natural environments, and diagnostic yields increased. The foundational work of Oxford Instruments will remain a cornerstone in the history of neurology.

Modern Ambulatory EEGs

The digital era in the 1990s transformed aEEG systems once again, introducing higher sampling rates, real-time analysis, and cloud-based storage. Monitoring EEG devices were now wireless, detection became automated, and multimodally were added by EEG monitoring companies. By the 1990s, lightweight aEEG systems were capable of recording 16 channels of data. Alongside these innovations came video-EEG, which greatly supplemented aEEGs. Nowadays, EEG monitoring companies like Neurotech make it easier for patients and clinicians by streamlining diagnostic workflows to improve patient outcomes.

Conclusion

Ambulatory EEG has completely changed how we approach brain diagnostics. Early designs focused on making testing portable and practical. Oxford Medilog’s systems were among the first to innovate in this area. By allowing testing in natural settings, patients feel more at ease. Modern systems now include features like cloud storage for easy access. EEG monitoring companies like Neurotech are helping make testing simpler for everyone. Ambulatory EEG has become crucial for understanding conditions like epilepsy. It’s proof that technology can truly improve patient care.