Researchers at MIT have developed a method to stimulate brain tissue using external magnetic fields and injected magnetic nanoparticles. The technique allows direct stimulation of neurons, which could be an effective treatment for a variety of neurological diseases, without the need for implants or external connections.

Previous efforts to stimulate the brain using pulses of electricity have proven effective in reducing or eliminating tremors associated with Parkinson’s disease, but the treatment requires highly invasive implanted wires that connect to a power source outside the brain.

“In the future, our technique may provide an implant-free means to provide brain stimulation and mapping,” said Polina Anikeeva, an assistant professor of materials science and engineering.

The team injected magnetic iron oxide particles, 22 nanometers in diameter, into the brain. When exposed to an external alternating magnetic field — which can penetrate deep inside biological tissues — the particles rapidly heat up.

The resulting local temperature increase can then lead to neural activation by triggering heat-sensitive capsaicin receptors — the same proteins that the body uses to detect both actual heat and the “heat” of spicy foods. The team used viral gene delivery to induce the sensitivity to heat in selected neurons in the brain.

The particles, which have virtually no interaction with biological tissues except when heated, tend to remain where they are placed, allowing for long-term treatment without the need for further invasive procedures.

The next step toward making the technology practical for clinical use in humans is to understand better how the method works through neural recordings and behavioral experiments, and to assess whether there are any other side effects to tissues in the affected area, says Anikeeva.