Neuroscientists at the University of Buffalo have used magnetic nanoparticles to directly control bodily movements of mice. According to researchers, the technique they developed called Magneto-Thermal Stimulation allows them to activate sections of the brain that cause mice to run, rotate or lose control of the extremities – an achievement that could eventually lead to advances in studying and treating neurological disease.

“There is a lot of work being done now to map the neuronal circuits that control behavior and emotions,” says lead researcher Arnd Pralle, PhD, a professor of physics in the University at Buffalo College of Arts and Sciences in a news release. “How is the computer of our mind working? The technique we have developed could aid this effort greatly.”

A section of a mouse brain with injected magnetic nanoparticles (red) covering targeted cells in the striatum
Picture shows a section of a mouse brain with injected magnetic nanoparticles (red) covering targeted cells in the striatum. Credit: Munshi et al, eLife

Earlier attempt on interfacing with the brain has used a technique called Transcranial Magnetic Stimulation, where researchers put magnetic coils a mere centimeter from the surface of the skull with high connectivity to the hippocampus to trigger specific activity in the brain. The technique has been shown to boost memory and ability to learn new things. Another one of the techniques, optogenetics, uses light instead of magnetism and heat to control neurons that have been genetically engineered to express light-sensitive ion channels. It also typically requires implantation of tiny fiber optic cables in the brain.

Magneto-Thermal Simulation instead uses magnetic nanoparticles to induce heat and activate individual neurons inside the brain. First, researchers use genetic engineering to introduce a special strand of DNA into targeted neurons so the cells produce temperature-activated ion channels. Then, they inject nanoparticles into the same area into the brain, where they latch onto the surface of the targeted neurons, forming a thin covering.

When an alternating magnetic field is applied to the brain, the nanoparticles’ magnetization flips rapidly, causing them to heat up the targeted cells. This in turn forces the temperature-sensitive ion channels to open, causing the neurons to fire. Researchers say the particles they used in the new study consisted of a cobalt-ferrite core surrounded by a manganese-ferrite shell.

“Using our method, we can target a very small group of cells, an area about 100 micrometers across, which is about the width of a human hair,” Pralle says.

Ion channels
This transmitted light image shows the striatum. The image is overlaid with a colored visualization highlighting cells (in green) that are targeted for neurostimulation. These cells have been infected with a virus that causes them to produce temperature-sensitive ion channels, which can be stimulated remotely via magnetic nanoparticle heating. Credit: Munshi et al, eLife

Arnd Pralle and his team tested their technique on mice and succeeded in activating three distinct regions of the brain to induce specific motor functions. They observed that stimulating cells in the motor cortex caused the mice to run, while stimulating cells in the striatum caused them to turn around. But stimulating a deeper region of the brain caused the mice to freeze completely.

Pralle says Magneto-Thermal Stimulation is a lot less invasive than optogenetics, and the mice which brains were simulated several times have shown no signs of brain damage.

The team says magneto-thermal stimulation technique would help them better understand how different parts of the organ communicate with one another and control behaviour. With it, they might be able to develop better treatments for diseases that involve the injury or malfunction of specific sets of neurons, such as traumatic brain injuries, Parkinson’s disease, dystonia and peripheral paralysis. And it could also aid scientists seeking to treat ailments such as depression and epilepsy directly through brain stimulation.

Their next step is to use magneto-thermal stimulation to activate — and silence — multiple regions of the brain at the same time in mice.

The study, entitled “Magneto-thermal genetic deep brain stimulation of motor behaviors in awake, freely moving mice” has been published in the journal eLife.

[University of Buffalo]