Directly stimulating the brain with magnetic pulses has been shown to help treat migraines and improve memory, but now scientists at the University of Buffalo have developed a technique that lets them directly control physical movements in mice. Using what they call magneto-thermal stimulation, the researchers activated sections of the brain that caused mice to run, turn or stop, in work that could eventually lead to new therapies for brain disorders or even mental illness.

Previous work on directly interfacing with the brain has used a technique called transcranial magnetic stimulation, where magnetic coils are placed against the skull to trigger specific brain activity. Along with improving memory and learning, it's been used to guide people through virtual mazes they'd never seen before and could even allow for brain-to-brain messaging. Another technique, called optogenetics, uses light pulses to interact with neurons that have been genetically engineered to react to light.

The Buffalo team's technique instead uses magnets to induce gentle heat and activate specific neurons. This magneto-thermal stimulation starts with mice that have been genetically engineered so the cells in the target neurons produce temperature-sensitive ion channels. Then, nanoparticles are injected into these parts of the brain, where they stick to the neurons. These particles are made of a cobalt-ferrite core coated in manganese-ferrite, and when an alternating magnetic field is applied, their magnetization flips back and forth, causing them to heat up. That in turn causes the ion channels to open, making those specific neurons fire.

"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," says Arnd Pralle, lead researcher on the study.

This transmitted light image shows sections of neural cells in the striatus that have been targeted for magnetic stimulation, in this case causing the mice to turn around(Credit: Munshi et al, eLife)

The team tested its technique on mice, targeting three different parts of the brain. By stimulating cells in the motor cortex, the mice would start running. Triggering the striatum made them turn around. And stimulating a deeper section of the brain made them stop completely.

While it might sound like a step towards remote-controlled mice, the Buffalo team's work was more directed at mapping specific parts of the brain to specific movements and behavior. With a better understanding of this enigmatic organ, scientists might be able to develop better treatments for illness or injury affecting specific neurons, including Parkinson's, peripheral paralysis, epilepsy and perhaps even depression.

"There is a lot of work being done now to map the neuronal circuits that control behavior and emotions," says Pralle. "How is the computer of our mind working? The technique we have developed could aid this effort greatly."

The researchers say magneto-thermal stimulation is less invasive than other techniques like optogenetics, and the mice it was tested on have shown no signs of brain damage. Their next step is to try to use the method to stimulate multiple parts of the brain at once.

The research was published in eLife.

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