Tiny Flexible Probes for Better Neural Interfaces

Researchers at the UC San Diego and Salk Institute have developed a tiny neural probe. It can be implanted for longer time periods to record and stimulate neural activity, while minimizing injury to the surrounding tissue.

"For chronic neural interfacing, you want a probe that's stealthy, something that the body doesn't even know is there but can still communicate with neurons," says research co-leader Donald Sirbuly in a press release issued by UC San Diego.

A paper is published in Nature Communications. It describes the new neural probe and the first tests on living laboratory mice.

The probe is five times thinner than a human hair, and flexible. It consists of an electrical channel and an optical channel. The electrical channel contains an ultra-thin polymer electrode. The optical channel contains an optical fiber that is also ultra-thin.

The probe can both record the electrical activity of neurons and stimulate specific sets of neurons using light. "Having this dual modality - electrical recording and optical stimulation - in such a small footprint is a unique combination," says Sirbuly.

According to the researchers, this type of neural probe is ideal for studying small and dynamic areas of the nervous system like peripheral nerves or the spinal cord.

"This is where you'd need a really small, flexible probe that can fit in between vertebrae to interface with neurons and can bend as the spinal cord moves," says research co-leader Axel Nimmerjahn.

The researchers implanted the probes in the brains of living mice. The probes caused hardly any inflammation in the brain tissue after prolonged implantation. As the mice moved about in a controlled environment, the probes were able to record electrical activity from neurons with high sensitivity.

The probes were also used to target specific neuron types to produce certain physical responses. Using the probes' optical channels, the researchers stimulated neurons in the cortex of the mice to move their whiskers.

"Currently, we know relatively little about how the spinal cord works, how it processes information, and how its neural activity might be disrupted or impaired in certain disease conditions," adds Nimmerjahn.

"It has been a technical challenge to record from this dynamic and tiny structure, and we think that our probes and future probe arrays have the unique potential to help us study the spinal cord - not just understand it on a fundamental level, but also have the ability to modulate its activity."

In the paper, the researchers note that the new probes allow both robust electrical measurement and optogenetic stimulation of the brain.

“Scalable fabrication strategies can be used with various electrical and optical materials, making the probes highly customizable to experimental requirements, including length, diameter, and mechanical properties,” they say.

“Given their negligible inflammatory response, these probes promise to enable a new generation of readily tunable multi-modal devices for long-term, minimally invasive interfacing with neural circuits.”

This seems to be a small but potentially very significant step toward the development of read/write brain machine interfaces.