Researchers at Massachusetts Institute of Technology (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. The research, conducted by Polina Anikeeva, an assistant professor of materials science and engineering, graduate student Ritchie Chen, and three others, has been published in the journal Science.
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 has remained a last resort because it requires highly invasive implanted wires that connect to a power source outside the brain.
In their study, the team injected magnetic iron oxide particles just 22 nm in diameter into the brain. When exposed to an external alternating magnetic field, which can penetrate deep inside biological tissues, these 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. Anikeeva's 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 nanoparticles integrate into the tissue and remain largely intact,” Anikeeva said. “Then, that region can be stimulated at will by externally applying an alternating magnetic field. The goal for us was to figure out whether we could deliver stimuli to the nervous system in a wireless and noninvasive way.”
The new work has proven that the approach is feasible, but much work remains to turn this proof-of-concept into a practical method for brain research or clinical treatment.