Dual-Purpose Neural Probe Enables New Capabilities

A new device that combines light delivery with a tetrode into a single neural probe may offer new ways of studying small clusters of brain cells.

Wei-Chuan Shih, a University of Houston Cullen College of Engineering assistant professor of electrical and computer engineering, said scientists generally must rely on two separate probes to study how neurons react to optical stimulation. The first probe delivers light to a specific area of the brain to stimulate cells, while the second records reactions of nearby neurons stimulated by the light probe at the single neuron level. The second probe, called a tetrode, consists of four thin twisted wires that are clipped along the same plane.

Using two probes, however, creates uncertainty.

“Once you insert the probes into the brain, you don’t know exactly where they are in relation to one another,” Shih said. This makes it difficult to know if a tetrode is tracking information from the same neurons stimulated by the light-delivery probe.

At the core of the new device, dubbed optitrode, is a classic tetrode, surrounded by the light-delivery portion of the probe, which consists of fused silica that acts as an optical waveguide. The entire device is enclosed in a rubberlike material that protects it from tissues it encounters. The current optitrode prototype measures 100 µm in diameter and 2 in. in length, enabling it to reach the deepest regions of the brain, where memory plays a significant role.

The device, developed by Shih and colleagues from Cullen and Baylor College of Medicine, will enable researchers to gather data with greater speed and precision because they will always know where each probe is. They also will be able to shine light directly onto the area monitored by the tetrode, Shih said.

Shih said neuroscientists should be able to create the optitrodes in their own labs because many already fabricate their own tetrodes. Integrating the light-delivery device is relatively simple and can be accomplished at low cost.

“This doesn’t need any kind of high-tech equipment,” he said. “It’s got a clever design and is very simple to make — not much more difficult than making a tetrode. It would be a nice addition to the tool kit that neuroscientists use in their labs.”

The device was described in Optics Letters.

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