A new research project has seen scientists wirelessly determine the path a mouse walks with a press of a button.

Researchers in the US have created a remote controlled, next-generation tissue implant that allows neuroscientists to inject drugs and shine lights on neurons deep inside the brains of mice.

“It unplugs a world of possibilities for scientists to learn how brain circuits work in a more natural setting,” said Dr Michael Bruchas, associate professor of anesthesiology and neurobiology at Washington University School of Medicine and a senior author of the study.

The Bruchas lab studies brain circuits behind a variety of disorders including stress, depression, addiction, and pain.

Usually, researchers have had to choose between injecting drugs through bulky metal tubes and delivering lights through fibre-optic cables. Both options require surgery that can damage parts of the brain and introduce experimental conditions that hinder animals' natural movements.

To address these issues, bioengineers in the Bruchas lab developed a remote controlled, optofluidic implant made out of soft materials that are a tenth the diameter of a human hair, which can simultaneously deliver drugs and lights.

“We used powerful nano-manufacturing strategies to fabricate an implant that lets us penetrate deep inside the brain with minimal damage,” said Dr John Rogers, professor of materials science and engineering at the University of Illinois, and a senior author.

“Ultra-miniaturised devices like this have tremendous potential for science and medicine.”

With a thickness of 80 micrometers and a width of 500 micrometers, the optofluidic implant is thinner than the metal tubes, or cannulas, scientists typically use to inject drugs.

When the researchers compared the implant with a typical cannula they found that the implant damaged and displaced much less brain tissue.

The scientists tested the device's drug delivery potential by surgically placing it into the brains of mice. In some experiments, they showed that they could precisely map circuits by using the implant to inject viruses that label cells with genetic dyes.

In other experiments, they made mice walk in circles by injecting a drug that mimics morphine into the ventral tegmental area (VTA), a region that controls motivation and addiction.

The researchers also tested the device's combined light and drug delivery potential. They managed to make mice that have light-sensitive VTA neurons stay on one side of a cage by commanding the implant to shine laser pulses on the cells.

The mice lost the preference when the scientists directed the device to simultaneously inject a drug that blocks neuronal communication. In all of the experiments, the mice were about a metre away from the command antenna.

“This is the kind of revolutionary tool development that neuroscientists need to map out brain circuit activity,” said researcher Dr James Gnadt.

The team fabricated the implant using semi-conductor computer chip manufacturing techniques. It has room for up to four drugs and has four microscale inorganic light-emitting diodes.

They installed an expandable material at the bottom of the drug reservoirs to control delivery. When the temperature on an electric heater beneath the reservoir rose then the bottom rapidly expanded and pushed the drug out into the brain.

“We tried at least 30 different prototypes before one finally worked,” said Dr McCall.

“This was truly an interdisciplinary effort,” said Dr Jeong.

“We tried to engineer the implant to meet some of neurosciences greatest unmet needs.”

In the study, the scientists provide detailed instructions for manufacturing the implant.

“A tool is only good if it's used,” said Dr Bruchas.

“We believe an open, crowd-sourcing approach to neuroscience is a great way to understand normal and healthy brain circuitry.”

The research report is accessible here.