Transparent Microelectrodes Allow for Dynamic Imaging to Study Epilepsy

The brain is the body’s control center, and it relies on an intricate circuitry of thousands of neurons that communicate with each other through electrical and chemical signals. An electroencephalogram (EEG), which is a recording of brain activity using small button electrodes, helps neuroscience researchers to better understand the cellular mechanisms involved with brain disorders, such as how epileptic seizures occur.

One of the most common disorders of the nervous system, epilepsy affects 2.7 million Americans of all ages, races, and ethnic background. A seizure takes place when spontaneous high-frequency bursting of neural networks appears that temporarily interrupts normal electrical brain function.

Neuroscience researcher Hajime Takano, PhD, who works in Douglas Coulter, PhD’s, epilepsy research laboratory at The Children’s Hospital of Philadelphia, is especially interested in which specific neurons could be inciting the neural network. But pinpointing those neurons’ locations and plotting the intensity of their activity in real time has been problematic because traditional metal electrodes cause interference when used in conjunction with sophisticated, multicellular calcium imaging techniques that investigators couple with high-speed microscopes to see and record when neurons are firing.

Dr. Takano, who is also a research assistant professor in the Neurology Department in the Perelman School of Medicine at the University of Pennsylvania, collaborated with other Penn researchers from the School of Engineering to test a new type of transparent, flexible microelectrode they developed that could solve this problem. It is made of the strongest material known to man: graphene, a two-dimensional form of carbon only one atom thick. Because it is see-through, the graphene microelectrode allows for simultaneous optical imaging and electrophysiological recordings of neural circuits.

“The idea of applying this technology to basic neuroscience for brain recording is something new and very exciting,” said Dr. Takano, who also has an engineering background.

In a study published in Nature Communications, Dr. Takano; senior author Brian Litt, PhD; Penn Engineering Postdoc Duygu Kuzum; and colleagues described how they were able to use the graphene microelectrode technology in combination with calcium imaging involving confocal and two-photon microscopy to observe seizure-like activity that they induced in neural tissue from rats. The investigators were able to obtain both high spatial and temporal resolution, which is the ability to discriminate between two points in space and time.

Neurons and their processes are small, with a spatial extent measured in micrometers. In contrast, the circuits within which neurons function may extend millimeters to a centimeter or more. The new microelectrode allows for dynamic imaging that can provide valuable information on individual cells, while at the same time probing the regions that they may span.

“By monitoring a seizure with the transparent electrodes and imaging individual neurons at the same time, we can try to pinpoint where a seizure started,” Dr. Takano said. “If there are repeated seizures, we can see if the seizure-initiating cell is always the same or not. And if there is an initiating cell, what is different about it?”

At the Society for Neuroscience’s Annual Meeting held Nov. 15-19 in Washington, D.C., Dr. Takano presented a poster describing how the study team used the graphene electrodes to record high-frequency bursting activity. The response from attendees was overwhelmingly positive, Dr. Takano said.

In the future, Dr. Takano plans to use the graphene electrodes in conjunction with other advanced imaging approaches to provide new insights into the functions of neural circuits during seizures. For example, they will allow him to use chloride imaging to explore factors that control the level of electrical activation in cellular regions.

Development of the transparent microelectrode technology involved a multidisciplinary effort from Penn’s new Center for NeuroEngineering and Therapeutics, Penn’s departments of Neuroscience, Pediatrics, and Materials Science, and the Division of Neurology at CHOP.