Magneto-thermal stimulation enables researchers to use heated, magnetic nanoparticles to activate individual neurons inside the brain.
Here’s how it works: First, scientists use genetic engineering to introduce a special strand of DNA into targeted neurons, causing these cells to produce a heat-activated ion channel. Then, researchers inject specially crafted magnetic nanoparticles into the same area of the brain. These nanoparticles latch onto the surface of the targeted neurons, forming a thin covering like the skin of an onion.
When an alternating magnetic field is applied to the brain, it causes the nanoparticles’ magnetization to flip rapidly, generating heat that warms the targeted cells. This forces the temperature-sensitive ion channels to open, spurring the neurons to fire.
The particles the researchers used in the new eLife study consisted of a cobalt-ferrite core surrounded by a manganese-ferrite shell.
An advance over other methods, like optogenetics
Pralle has been working to advance magneto-thermal stimulation for about a decade. He previously demonstrated the technique’s utility in activating neurons in a petri dish, and then in controlling the behaviour of C. elegans, a tiny nematode.
Pralle says magneto-thermal stimulation has some benefits over other methods of deep-brain stimulation.
One of the best-known techniques, optogenetics, uses light instead of magnetism and heat to activate cells. But optogenetics typically requires implantation of tiny fibre optic cables in the brain, whereas magneto-thermal stimulation is done remotely, which is less invasive, Pralle says. He adds that even after the brains of mice were stimulated several times, targeted neurons showed no signs of damage.
The next step in the research is to use magneto-thermal stimulation to activate — and silence — multiple regions of the brain at the same time in mice. Pralle is working on this project with Massachusetts Institute of Technology researcher Dr. Polina Anikeeva, and Harvard Medical School.
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