Tiniest LED Implants Let Probes Illuminate Brain

Researchers have built neural probes that hold what may be the smallest implantable LEDs ever made.

These new probes can control and record the activity of many individual neurons, measuring how changes in the activity of a single neuron can affect its neighbors.

The team, which has tested the probes in mice, anticipates that experiments using probes based on their design could lead to breakthroughs in understanding and treating neurological diseases such as Alzheimer’s. Says Kensall Wise, professor emeritus of the University of Michigan, who was involved with the research:

“This is a very big step forward. The fact that you can generate these optical signals on the probe, in a living brain, opens up new doors.”

A network of around 100 billion neurons power the human brain, and figuring out how they work together is a monumental and important task, the researchers say.

“Hundreds of millions of people suffer from neurological diseases, but treatment methods and drugs are currently very limited because scientific understanding of the brain is lacking,”

says Fan Wu, a postdoctoral researcher in electrical engineering and computer sciences and co-first author of a new paper on the findings in Neuron.

“We have developed a tool that is needed to better understand how the brain works—and why it doesn’t work—to try to solve to these problems.”

Probes the Size of Neurons

In genetically modified rodents, neurons can be turned on and off with light.

Typically, neuroscientists using this optogenetics technique shine light on a region of the brain through implanted optical fibers and record the response with a second device.

This helps to reveal which regions of the brain are responsible for which behaviors. But it can’t reveal how the neurons communicate with one another.

The new probes can. Each probe array contains 12 LEDs and 32 electrodes. The micro LEDs are as small as a neuron’s cell body, so they can turn single neurons on and off.

neural probe

The tines of the neural probe are just under a tenth of a millimeter wide. Equipped with minuscule LED lights and electrodes, each tine can stimulate and measure about a hundred individual neurons. (Credit: Fan Wu)

Meanwhile, the microelectrodes measure activity at the single-neuron level, reporting how a change in one neuron’s behavior affects the surrounding network.

“Now we can know how a group of cells, both adjacent and farther away, are responding to the activation of a single cell,” Wu says. “This will help us better understand how these cells are communicating with each other.”

Searching for Memories

While the probes were made at the University of Michigan, the experiments to demonstrate them took place at New York University in the lab of György Buzsáki, a leader in experimental neuroscience.

Eran Stark, who is currently an assistant professor of neuroscience at Tel Aviv University, used them to measure how signals pass through the brains of mice. He focused on the area of the brain responsible for short- and long-term memory.

“Using micro-LED probes, we may tease out how the signals propagate inside the neural circuitry so that we can understand how memories are formed, retrieved, and replaced,”

says Euisik Yoon, a professor of electrical engineering and computer science at the University of Michigan and project leader.

The proof-of-concept experiment found that superficial and deep neurons in the hippocampus produce different kinds of brain waves when stimulated. Future experiments will explore how these waves are related to memory.

Fan Wu5 , Eran Stark5 , Pei-Cheng Ku , Kensall D. Wise , György Buzsáki, Euisik Yoon
Monolithically Integrated μLEDs on Silicon Neural Probes for High-Resolution Optogenetic Studies in Behaving Animals
Neuron DOI: http://dx.doi.org/10.1016/j.neuron.2015.10.032

Top Photo: Luis Pérez/Flickr